Unit - 3

Transition Elements-2

3.1 Transition Elements -2: Chemistry of Ti, V, Cr, Mn, Fe and Co in various oxidation states (excluding their metallurgy)

3.1.1 D-Block elements:

The elements in the D block are those that can be found in the current periodic table from the third to the twelfth groups. These elements' valence electrons are located in the d orbital. Transition elements or transition metals are other names for D block elements. The following article contains the first three rows of the d block elements, which correspond to the 3d, 4d, and 5d orbitals, respectively.

What are D Block Elements?

D block elements are those that have electrons (1 to 10) in the d-orbital of the penultimate energy stage and in the outermost ‘s' orbital (1-2). Despite the fact that electrons do not occupy the ‘d' orbital in group 12 metals, their chemistry is close to that of the preceding groups in several respects, and they are thus classified as d block elements.

Metallic properties such as malleability and ductility, high electrical and thermal conductivity, and strong tensile strength are characteristic of these elements. The d block has four sequence that correspond to the filling of 3d, 4d, 5d, or 6d orbitals.

There are 10 elements filling up the ‘d’ orbital in each series.

Position of D Block Elements in Periodic Table

Columns 3 to 12 are occupied by D block elements, which can have atoms with fully filled ‘d' orbitals. A transition metal is described by the International Union of Pure and Applied Chemistry as "an element whose atom or cations has a partially filled d sub-shell."

Why D Block Elements are called Transition Elements?

Groups 4–11 are made up of transition elements. Transition elements include scandium and yttrium from Group 3, which have a partially filled d subshell in the metallic state. Elements in the 12 column of the d block, such as Zn, CD, and Hg, have fully filled d-orbitals and are thus not called transition elements.

Transition Elements get their name from the fact that they are placed between s and p block elements and have properties that transition between them. So, although all transition metals are d block elements, they are not all transition elements.

Properties of Transition Metals

1. Electrons are attached to the ‘d' sub-orbitals, which are located between the (n+1) s and (n+1) p sub-orbitals.

2. In the periodic table, it is located between the s and p block elements.

3. The differences in properties between the s and p-block elements.

Electronic Configuration of D Block Elements

The electronic configuration of D block elements is (n-1) d 1-10ns 1-2. Half-filled orbitals and fully filled d orbitals are both stable for these elements. The electronic structure of chromium, which has half-filled d and s orbitals in its configuration – 3d54s1, is an example of this. Another example is the electronic configuration of copper. Copper has a 3d104s1 electronic structure rather than a 3d94s2.

The relative stability of the fully filled d orbital can be due to this. In both their ground and general oxidation states, zinc, mercury, cadmium, and copernicium have fully filled orbitals. As a result, these metals aren't classified as transition elements, whereas the others are classified as d block elements.

1. For time 4, transition components, the electronic configuration is (Ar) 4s 1-2 3d 1-10.

2. For time 5, transition elements, the electronic configuration is (Kr) 5s 1-2 4d 1-10.

3. For time 6, transformation components, the electronic configuration is (Xe) 4s 1-2 3d 1-10.

According to the Aufbau principle and Hund's rule of multiplicity, electrons are added to the 3d subshell from left to right along the time.

Many of the series have anomalies, which can be explained by the following factors.

The difference in energy between the ns and (n-1) d orbitals.

2. Pairing energy for s-orbital electrons

3. Half-filled orbitals are stable as compared to partially filled orbitals.

Chromium has a 4s13d5 electron configuration rather than a 4s23d4 electron configuration, while copper has a 4s13d10 electron configuration rather than a 4s23d9. The stability of half-filled orbitals compared to partially filled orbitals explains these inconsistencies in the first transition sequence.

From niobium onwards, electron presence in d orbitals tends to be favoured over electron sharing in s orbitals in the second sequence of transition metals. The electron can choose between sharing in the s orbital or being excited to the d orbital from the available s and d orbitals. Obviously, the option is determined by the amount of repulsive energy overcome during sharing and the energy difference between the s and d-orbitals.

Since the s and d-orbitals have almost the same energy in the second series, electrons tend to occupy the d-orbital. As a result, s-orbital has only one electron in niobium. Transition metals in the third sequence, on the other hand, have a higher number of paired s configurations, even at the cost of half-filled orbitals (Tungsten- 6s25d4). This sequence follows the filling of 4f orbitals and the lanthanide contraction that follows.

Because of the smaller scale, the ‘f' electron provides a lot of shielding for the d orbitals. The energy difference between the s and 5d orbitals is increased as a result of the shielding, and the pairing energy is less than the excitation energy. Despite the stability provided by half-filled orbitals, tungsten does not allow for electron excitation.

Atomic and Ionic Radii of D Block Elements

Metallic Radii of 1st, 2nd, and 3rd Row Transition Metals

Atomic and ionic radii of elements of all three-transition series

1. Rapidly decreases from column 3 to column 6.

2. From column 7 to 10, it stays the same, and 3. From column 11 to 12, it starts to increase.

For e.g., in the first transition sequence, atomic radii, the decrease is greater from Sc to Cr (group 3 to 6), and is nearly the same for Mn, Fe, Co, Ni (group 7,8, 9 &10), with an increase in Cu and Zn.

1. The greater reduction in atomic radii in column 3 to 6 elements is due to an increase in effective nuclear charge, but insufficient shielding due to the fewer d-electrons.

2. The repulsion between the mutual d electrons in elements in column 7 to 10 balances the increasing effective nuclear charge, resulting in the same radii.

3. The d orbital is filled with ten electrons in 11 and 12 column components, shielding the electrons in the higher s-orbital. As a result, group 11 and 12 elements such as Cu and Zn are larger than the block's earlier elements.

The radii of the third series elements are to be greater than the radii of the second series elements since electrons occupy a higher orbital. However, the radii of both series are nearly identical. The 5d orbitals in the third series elements are filled only after the 4f orbitals have been filled, raising the effective nuclear charge by 14 units.

Lanthanide contraction is a term used to describe the greater shrinkage of radii caused by a higher nuclear charge. The increased nuclear effective charge effectively neutralises the rise in radii due to the higher orbital. As a result, the atomic radii of the second and third series elements are the same. Niobium and hafnium, for example, have almost identical atomic radii.

Properties of D Block Elements

Ionization energy is the amount of energy required to detach the valence electron from an atom/ion, and it is proportional to the electron's force of attraction. As a result, the ionisation energy increases as the nuclear charge and electron radii decrease (IE). For half-filled and completely filled orbitals, the ionisation energy would be higher.

The ionisation energy of the d block elements is higher than that of the s-block and lower than that of the p-block elements, which they are sandwiched between. Except for chromium and copper, the first Ionization Energy sequence requires removal from a filled s-orbital. The Ionization Energy of d block elements increases as the atomic number increases up to Fe.

In Co and Ni, increasing the share of d-electrons compensates for the rise in atomic number, lowering the Ionization Energy. As s-block elements, copper and zinc display increasing IE. Niobium elements in the second sequence have single electrons in the s-orbital.

As a result, they display a steady rise in IE as the atomic number increases. Palladium, on the other hand, has a complete d-shell and no electrons in the s-shell. As a result, Pd displays the highest IE. The attraction of electrons by the nuclear charge is much stronger in lanthanide contraction, so IE of 5d elements is much greater than 4d and 3d elements. Except for Pt and Au, all elements in the 5d sequence have a filled s-shell.

From Hafnium to Rhenium, the IE is the same, and after that, the IE increases with the number of mutual d-electrons, with Iridium and Gold having the highest IE.

High tensile strength, malleability, ductility, electrical and thermal conductivity, metallic lustre, and crystallisation in bcc/ccp/hcp structures are all characteristics of D block elements.

Except for Copper, they are extremely hard and have a high enthalpy of atomization and low volatility. The number of unpaired electrons increases the hardness. As a result, among the d block elements, Cr, Mo, and W are extremely hard metals. In this regard, the group-12 elements (Zn, Cd, and Hg) are also an exception.

The oxidation state is a hypothetical state in which the atom tends to lose or gain more electrons than it does in its normal valency state. It's also useful for demonstrating the atom's/properties. ion's Both s and d-orbitals may have electrons in transition elements/ions.

Since the energy difference between the s and d orbitals is small, both electrons will participate in the formation of ionic and covalent bonds, resulting in multiple(variable) valency states (oxidation states).

As a result, each transition element may have a minimum oxidation state equal to the number of s-electrons and a maximum oxidation state equal to the total number of electrons in both s and d-orbitals. Between oxidation states, new oxidation states become possible.

Cr, Cu, Ag, Au, and Hg all have a minimum Oxidation state of 1.

2. Oxidation state becomes more stable in the order 3d 4d 5d. The elements of the 3d series are the most stable in +2, the 4d series in +2 and +4, and the 5d series in +4. In their higher OS, Cr6+ and Mn7+ (of 3d) are not stable. CrO42- and MnO4– containing compounds are highly reactive and strong oxidising agents.

In their higher OS, Mo6+ and Tc7+ (of 4d) are stable. MoO42- and TcO4– containing compounds are unreactive and stable. W6+ and Re7+ (of 5d) are similarly stable in their higher OS. Compounds containing them, such as WO42- and ReO4–, are safe and unreactive.

Higher oxidation states (+2 and +3) of cations of the second and third-row transition metals are much easier to oxidise than the corresponding ions of the first-row transition metals. The most stable chromium compounds are Cr (III), while the corresponding Mo (III) and W(III) compounds are highly reactive.

In fact, they are frequently pyrophoric, igniting when exposed to oxygen in the air. As we'll see, the heavier elements in each group form stable compounds in higher oxidation states that don't have analogues in the group's lightest member.

3. Strongly oxidising elements with a high oxidation number form oxides and fluorides rather than bromides and iodides.

Just VO4–, CrO42–, MnO4–, VF5, VCl5, VBr3, VI3 and not VBr5, VI5 type vanadium. Because of its high electronegativity and small scale, V5+ oxidises Br– and I– to Br2 and I2, but not fluoride.

Bromides and iodides, rather than oxides and fluorides, are formed by strongly reducing, low oxidation number elements.

4. Middle-order elements in each sequence have the highest oxidation state, which is equal to the s and d-electrons. Manganese in the 3d series has a maximum oxidation state of +7, Ru in the 4d series has a maximum oxidation state of +8, and Os in the 5d series has a maximum oxidation state of +8.

5. Elements can show all Oxidation states in the range of minimum to maximum.

6. Elements in their lower oxidation states will be ionic and basic (TiO, VO, CrO, MnO, TiCl2, and VCl2), in-between state amphoteric (Ti2O3, V2O3, Mn2O3, CrO3, Cr2O3, TiCl3, VCl3, VCl3), and higher oxidation state covalent and acidic (V2O5, MnO3, Mn2O7,

7. Back bonding in complexes can help to stabilise lower oxidation states. [Ag (CN)2] Ni (CO)4, Fe (CO)5, [Ag (NH3)2] –, +

Lower oxidation states in these metals are stabilised by pi-electron donors such as CO, while higher oxidation states are stabilised by electronegative elements such as Fluorine(F) and Oxygen (O). As a result, these metals' high oxidation compounds are mostly fluorides and oxides.

8. Several factors influence the relative stabilities of oxidation states, including the stability of the resulting orbital, IE, electronegativity, enthalpy of atomization, enthalpy of hydration, and so on.

1. Ti4+ (3d0) has a higher stability than Ti3+ (3d1). Mn2+ (3d5) has a higher stability than Mn3+ (3d4).

2. Ionization energies play a role in transition metal compounds' relative stability (ions). Ni2+ compounds, for example, are more thermodynamically stable than Pt2+ compounds, while Pt4+ compounds are more stable than Ni4+ compounds. The following is how the relative stabilities can be clarified.

As a result, the energy needed to ionise Ni to Ni2+ is lower (2490 kJ mol1) than the energy required to produce Pt2+ (2660 kJ mol1). As a result, Ni2+ compounds are more stable thermodynamically than Pt2+ compounds.

In comparison to the energy needed for the formation of Ni4+ (11290 kJ/mol), the formation of Pt4+ requires less energy (9360 kJ mol1). Pt4+ compounds are therefore more stable than Ni4+ compounds. The fact that the [PtCl6]2+ complex ion is known, while the corresponding ion for nickel is unknown, supports this theory.

The heavier elements in the p-block prefer lower oxidation states due to the inert pair effect. Higher oxidation states are more stable for heavier members of a group in the case of d block elements.

Electrode Potential in D Block Elements

The electrode potential data can be used to predict the relative stabilities of transition metal ions in various oxidation states in the aqueous medium. A cation's oxidation state would be more stable if H (Hsub + lE + Hhyd) or E° is more negative (for less positive).

1. As the series progresses, E° becomes less negative, meaning that the reduced state is more stable.

2. Transition elements have a low E° as compared to first and second group metals.

Physical Properties of D Block Elements

Density: Among the transition series, the trend in density will be reverse of atomic radii, i.e., density increase remains almost the same and then decreases along the period.

When you go down the column, the column density of the 4d series is higher than that of the 3d series. Due to lanthanide contraction and a greater decrease in atomic radii, the volume density of transition elements in the 5d series is double that of the 4d series.

In the 3d series, scandium has the lowest density, while copper has the highest density. Osmium (d=22.57g cm-3) and Iridium (d=22.61g cm-3) are the 5d sequence elements with the highest density of all the d block elements.

Some d block elements with relative radii are Fe Ni Cu, Fe Cu Au, and Fe Hg Au.

Why D Block Elements have high Melting and Boiling Point?

In addition to the metallic bonding formed by s-electrons, unpaired electrons and empty or partially filled d-orbitals form covalent bonding. D-block elements have higher melting and boiling points than s and p block elements due to their heavy bonding. This pattern continues until the d5 configuration, after which it reverses as more electrons in the d-orbital pair.

1. In their sequence of elements, Cr, Mo, and W have the highest melting at boiling point.

2. The half-filled configuration of manganese (Mn) and technetium (Tc) results in poor metallic bonding and abnormally low melting and boiling points.

3. There are no unpaired d-electrons in Group 12, Zn, Cd, or Hg, because there is no covalent bonding. They will have the lowest melting and boiling points in the game.

Mercury is the only metal that can remain in a liquid state at room temperature. Mercury's 6s valence electrons are more closely pulled by the nucleus (lanthanide contraction), resulting in less involvement of outer s-electrons in metallic bonding.

What Transition Elements are Considered Noble Metals?

In the three-transition series

1. The ionisation energies of elements gradually increase over a row.

2. From the left corner of the 3d series to the right corner of the 5d transition elements, density, electronegativity, electrical, and thermal conductivities increase, while metal cation hydration enthalpies decrease.

This means that the transition metals are gradually becoming less reactive and more "noble" in nature. Metals (Pt, Au) in the lower right corner of the d block have such high ionisation energies, increasing electronegativity, and decreasing low enthalpies of hydration that they are often referred to as "noble metals."

Magnetic Properties of D Block Elements

The interaction of materials with the magnetic field is defined as follows:

If it is repelled, it is diamagnetic; if it is attracted, it is paramagnetic; and if it is ferromagnetic, it will maintain its greater magnetic nature even in the absence of a magnetic field.

Diamagnetism is caused by paired electrons. Para-magnetism is caused by unpaired electrons, whereas ferromagnetism is caused by unpaired electrons aligned together. Depending on the unpaired electrons, D block elements and their ions show this behaviour.

The ‘orbital magnetic moment' and the ‘spin magnetic moment' are both influenced by unpaired electrons. The orbital angular moment is negligible in the 3d series, so the estimated spin-only magnetic moment is given by the formula:

= [4s (s + 1)] = [4s (s + 1)] = [4s (s + 1)] = [4s (s [n (n + 1)] = [n (n + 1)] = [n (n + 1)] = [n (BM

where ‘n' is the number of unpaired electrons and ‘S' is the total spin. Bohr Magneton is its unit (BM). The real magnetic moment for higher d-series involves elements from the orbital moment as well as the spin moment. The maximum number of unpaired electrons and magnetic moment are found in chromium and molybdenum.

Formation of Coloured Ions by D Block Elements

D block element compounds come in a number of colours. When a frequency of light is absorbed, the light emitted has a complementary colour to the absorbed frequency. Transition element ions can absorb visible frequency and use it in two ways, resulting in visible colour.

1. d-d Transition

Excitation of an electron to a higher energy level is one process. The presence of a d-electron and an empty d-orbital in transition element ions can result in colour formation. Excitation and de-excitation of valence electrons. This is referred to as a d-d transition.

D-orbitals are degenerate and have the same energy as D-orbitals. The presence of ligands capable of forming coordinate bonds with these ions removes the degeneracy and divides the d-orbitals into two groups: e.g., and t2g. The intensity of the incoming ligand determines the energy difference (E).

By absorbing energy in the visible region (=400-700nm) and transmitting (giving) a complementary colour, electrons in the lower d-orbitals can be excited into the higher d-orbitals.

[Cu (H2O)6] 2+ ions, for example, absorb red radiation and look complementary blue-green. In the sunlight, hydrated Co2+ ions absorb radiation in the blue-green zone and look red.

Cupric ion is colourless and in the presence of water molecules becomes blue in colour.

a) The colour of the ion’s changes depending on their oxidation state. Cr6+ is yellow in colour, similar to potassium dichromate, while Cr3+ and Cr2+ are green and blue, respectively.

b) The compound's colour is also affected by the complexing or coordinating group. Cu2+, for example, has a light blue colour when it is liganded with water, but a deep blue colour when it is liganded with ammonia.

c) Transition metal ions, which have the following properties:

1. D-orbitals that are fully filled and have no empty d-orbitals for electron excitation are colourless. Cu+(3d10), Zn2+(3d10), Cd2+(4d10), and Hg2+(5d10) are colourless metals.

2. Colourless transition metal ions are those with fully empty d-orbitals and no d-electrons. The ions Sc3++(3d0) and Ti4++(3d0) are colourless.

d – p bonding L-M and M-L

Ligands will donate their p electrons to metal ions' empty d orbitals. This interaction, also known as ligand-metal / metal-ligand or d – p bonding, can give compounds colour.

Complex Formation Tendency of D Block Elements

A complex compound is one in which a metal is bound to a variety of neutral molecules or anions. Because of their small ionic scale, high charge, and relative availability of d orbitals for bond formation, metals from the d block form a variety of complex compounds.

Metals in transition and their ions They will attract electrons and receive lone pairs of electrons from anions and neutral molecules into their empty d-orbitals, forming coordinate bonding, due to their larger nuclear charge and smaller size.

With CO, NO, NH3, H2O, F–, Cl–, and CN–, transition elements form complex molecules. [Co (NH3) 6] 3+ [Cu (NH3)4] 2+, Y (H2O) 6]2+, [Fe (CN)6]4, [FeF6] 3, [Ni (CO)4] are examples of transition metal complexes.

Catalytic Activity of Elements

Catalysts are crucial in the industrial processing of many chemicals in bulk. Many d-block elements are used as catalysts in chemical and biological reactions since they are metals in their ionic form.

Some very important commercial catalytic processes involving d block metals include iron in Haber's process to make ammonia, vanadium pentoxide in the manufacture of sulphuric acid, titanium chloride as Zigler Natta catalyst in polymerization, and palladium chloride in the conversion of ethylene to acetaldehyde.

Most transition elements act as good catalyst because of,

1. The existence of d-orbitals that are vacant.

2. The proclivity for varying oxidation states.

3. The proclivity for reactants to form reaction intermediates.

4. They have defects in their crystal lattices.

They take the reaction through a path of low activation energy by:

1. Providing a broad surface area for absorption and enough time to react;

 2. Interacting with the reactants through their empty orbitals.

3. Their multiple oxidation states can interact actively through redox reaction.

Alloy Formation in D Block Elements

The atomic radii of transition elements in either sequence is very similar to one another. As a consequence, they can quickly swap places in the lattice and form solid solutions over a wide range of compositions. Alloys may be formed when the difference in radii is less than 15%.

Alloys are robust solutions like this. Alloys are solid solutions of two metals or a metal with a non-metal that are homogeneous in nature. In comparison to the host metal, transition metal alloys are hard and high melting metals.

Steels are iron alloys containing metals such as chromium, vanadium, molybdenum, tungsten, manganese, and other elements. The following are some important alloys:

Cu (75-90%) + Sn (10-25%) in bronze; Cr (75-90%) in chromium steel (2-4 percent of Fe) Stainless steel contains Cr (12-14%) and Ni (2-4%) of Fe; solder contains Pb + Sn.

Interstitial Compounds of D Block Elements

A void exists in the crystal lattice structure of transition metals. During crystal structure formation, small non-metallic atoms and molecules such as hydrogen, boron, and carbon may become trapped in the void. Interstitial compounds are what they're called. They are non-stoichiometric and neither ionic nor covalent, as in TiH1.7 and VH0.56.

The properties of interstitial compounds are as follows:

1. They have very high melting points.

2. They are incredibly difficult.

3. As compared to other metals, they have similar conductivity properties.

4. They are chemically inert and are unreactive.

TiC, Mn4N, Fe3H, and TiH2 are examples of interstitial compounds formed with transition metals.

Non-Stoichiometric Compounds

Different oxidation states of transition metal compounds may often be found together. They may be caused by a flaw in the solid structure or by the environment. This mixture, however, behaves as though it were a single compound.

This compound will not have a specified structure or composition. When group16 (O, S, Se, Te) elements are combined, non-stoichiometric behaviour is evident. Fe0.94O, Fe0.84O, VSe0.98, Se1.2 are some examples.

Important Compounds of D Block Elements

The D Block Elements are used to make a variety of important industrial compounds. Some examples of such compounds are:

1. K2Cr2O7 (Potassium Dichromate): In the leather industry, this compound is extremely essential. In most azo compound preparation methods, it is often used as an oxidant.

The dichromate ion is made up of two tetrahedra that share a single corner with a bond angle of 1260 between Chromium, Oxygen, and Chromium. Potassium dichromate is a strong oxidizer. In the method of volumetric analysis, potassium dichromate is also used as a primary norm.

KMnO4 is the second element in the KMnO4 formula (Potassium Permanganate)

The physical appearance of KMnO4 is intensely purple. It has diamagnetic properties as well as poor paramagnetic properties that are temperature dependent.

The lack of unpaired electrons in the permanganate ion causes diamagnetism. In organic chemistry, potassium permanganate is often used as an oxidant in the preparation of various materials. It can also be used to bleach cotton, silk, and wool. Because of its high oxidising capacity, it can also be used to decolorize oils.

3.1.2 Neutral-Atom Electron Configurations

It's easy to figure out which electrons are in which orbitals by counting through the periodic table. As previously mentioned, the number of electrons in a neutral atom can be determined by counting protons (atomic number). This process can be sped up by organising by block. Please refer to the section on electron configuration if you have any doubts about this counting system or how electron orbitals are filled.

For instance, if we wanted to figure out the electronic structure of Vanadium (atomic number 23), we'd start with hydrogen and work our way down the Periodic Table.

1s (H, He), 2s (Li, Be), 2p (B, C, N, O, F, Ne), 3s (Na, Mg), 3p (Al, Si, P, S, Cl, Ar), 4s (K, Ca), 3d (H, He, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be, Li, Be (Sc, Ti, V).

This organisation is verified by looking at the periodic table below. In the third orbital, we have three components. As a result, we write the orbitals in the order in which they were filled.

1s2 2s2 2p6 3s2 3p6 4s2 3d3 1s2 2s2 2p6 3s2 3p6 4s2 3d3

or

4s2 3d3 [Ar]

The neutral atom configurations of the fourth period transition metals are in Table 22.

Copper and chromium tend to be outliers. Take a quick glance at the Periodic Table to see where the element Chromium (atomic number 24) falls (Figure 11). Chromium has the electronic structure [Ar] 4s13d5 rather than [Ar] 4s23d4. Since a partially filled 3d manifold (with one 4s electron) is more stable than a partially filled d-manifold, this is the case (and a filled 4s manifold). Table 22 shows that the copper experiences a similar anomaly, despite having a totally filled d-manifold.

3.1.3 Multiple Oxidation States

Since transition metals are relatively quick to lose electrons compared to alkali metals and alkaline earth metals, most of them have several oxidation states. The valence s-orbital of alkali metals has one electron, and their ions almost always have oxidation states of +1. (From losing a single electron). Alkaline earth metals, on the other hand, have two electrons in their valence s-orbitals, resulting in ions with a +2-oxidation state (from losing both). Transition metals, on the other hand, are more complex, with a wide variety of detectable oxidation states due to the removal of d-orbital electrons. The most common oxidation states of period 3 elements are depicted in the chart below.

Scandium is one of only two transition metal elements with only one oxidation state (the other being zinc, which has an oxidation state of +2). The oxidation states of all the other elements are at least two. Manganese, which is found in the middle of the era, has the most oxidation states, and therefore the highest oxidation state in the entire period, since it contains five unpaired electrons (see table below).

It's important to note the pattern when it comes to the stability of higher oxidation states for transition metals: the stability of higher oxidation states gradually increases down a group. For example, Cr is most stable at a +3-oxidation state in group 6, which means that stable Cr forms in the +4 and +5 oxidation states are rare. At +4 and +5 oxidation states, however, there are several stable forms of molybdenum (Mo) and tungsten (W).

Key takeaway:

1. The presence of several oxidation states divided by a single electron characterises transition metals.

2. The majority of transition-metal compounds are paramagnetic, while nearly all p-block element compounds are diamagnetic.

3. There are two forms of electronic transitions in transition metal compounds that trigger their colours.

4. Transition metals may form paramagnetic compounds due to the presence of unpaired d electrons.

5. All of the d-electrons in diamagnetic compounds are paired up.

6. Transition metals are electrical conductors with high density and melting and boiling points.

3.2 Lanthanoids and Actinoids: Electronic configuration, oxidation states, colour, spectral and magnetic properties

3.2.1 F-block:

The elements of the F block are divided into two groups: lanthanoids and actinoids. These elements are known as inner transition metals because they provide a transition between the s and d blocks of the periodic table in the 6th and 7th rows.

What are F Block Elements?

F block elements are those that have their f orbital packed with electrons. These elements have electrons in the f orbital (1 to 14), the penultimate energy level's d orbital (0 to 1), and the outermost's orbital.

The f block has two sequence that led to the filling of 4f and 5f orbitals. The components are the Ce to Lu 4f series and the Th to Lw 5f series. In each sequence, the ‘f' orbital is filled with 14 elements.

The position of F Block Elements in the Periodic Table: F block elements are

put at the bottom of the periodic table separately They're a combination of the 6th and 7th periods.

Classification of F Block Elements

The elements of the f block are further classified as follows:

1. The first group of elements is known as the lanthanides, and it consists of elements with atomic numbers ranging from 57 to 71. These are non-radioactive elements (except for promethium, which is radioactive).

2. Actinides are the second group of elements, which includes elements with atomic numbers ranging from 89 to 103. The majority of these elements are radioactive.

The following is a list of all the f block elements. The row that starts with Lanthanum contains all of the lanthanides, while the row that starts with Actinium contains all of the actinides.

F block Elements as Inner Transition Elements

In terms of transition metal naming, f block elements are referred to as inner transition elements since the f orbital is much closer to the centre than the d orbital.

Properties of F block Elements

1. Add electrons to the (n-2) level 2's 'f' sub-orbitals. In the periodic table, they are found between the (n-1) d and ns block elements.

3. Properties are comparable to those of d-block elements.

Lanthanides vs. Actinides: What's the Difference?

1. The filling of 4f-orbitals is done by lanthanoids, whereas the filling of 5f-orbitals is done by actinoids. The binding energy of 4f electrons is lower than the binding energy of 5f electrons. When compared to 4f-electrons, the shielding effect of 5f-electrons is less efficient.

2. The paramagnetic properties of lanthanoids are simple to describe, but actinoids are more difficult to explain.

3. Lanthanides, with the exception of promethium, are non-radioactive in nature, whereas all actinide sequence elements are radioactive.

4. While lanthanides have a low proclivity for forming oxo-cations, the actinide sequence has many oxo-cations. The compounds formed by lanthanides are less basic than those formed by actinides, which are extremely basic.

Similarities between Lanthanides and Actinides

The filling of the (n-2) f subshell distinguishes the elements of the lanthanide and actinide series. They have almost identical outermost electronic configurations and, as a result, have similar properties. The following are some notable parallels:

1. They both have a prominent +3 oxidation state.

2. They play a role in filling (n-2) f orbitals.

3. They have a high electro positivity and are extremely reactive.

4. As the atomic number increases, the atomic and ionic size decreases.

5. They're both magnetic in nature.

3.2.2 Lanthanides:

What are Lanthanides?

Lanthanides are the rare earth elements in the current periodic table, which include elements with atomic numbers ranging from 58 to 71 after Lanthanum. Rare earth metals are so called because they only make up a small percentage of the Earth's crust (310-4 percent). As lanthanide orthophosphates, they can be found in ‘monazite' sand. In the year 1925, the Norwegian mineralogist Victor Goldschmidt coined the word "lanthanide." All but one of the fifteen metallic elements in the lanthanide family (from lanthanum to lutetium) are f-block elements. These elements' valence electrons are in the 4f orbital. Lanthanum, on the other hand, is a d-block element with a [Xe]5d16s2 electronic configuration.

Lanthanides are extremely dense elements, ranging in density from 6.1 to 9.8 grammes per cubic centimetre. These elements, like most metals, have extremely high melting and boiling points (ranging from 800 to 1600 degrees Celsius) (ranging from roughly 1200 to 3500 degrees Celsius). Ln3+ cations are known to form in all lanthanides.

Lanthanides are extremely dense metals with melting points that are much higher than those of the d-block elements. They combine with other metals to form alloys. These are the inner transition metals, which are also known as the f block elements. In the inner transition elements/ions, electrons can be found in the s, d, and f orbitals.

Properties of Lanthanide Series

If we consider the lanthanides and actinides series in the periodic table for transition metals, the table would be too broad. These two series, known as the 4f series (Lanthanoids series) and 5f series, are found at the bottom of the periodic table (Actinoids series). Inner transition elements are the 4f and 5f series put together.

In terms of chemical and physical properties, all of the elements in the sequence are very similar to lanthanum. The following are some of the most important characteristics and properties:

1. They have a lustrous sheen to them and look silvery.

2. They're made of soft metals that can be sliced with a knife.

3. Depending on their basicity, the elements have different reaction tendencies. Some people are quick to respond, while others take their time.

4. If contaminated with other metals or non-metals, lanthanides will corrode or become brittle.

5. They almost all combine to form a trivalent compound. They can also form divalent or tetravalent compounds on occasion.

6. They are attracted to each other.

Lanthanide Contraction

Due to increasing nuclear charge and electrons joining the inner (n-2) f orbital, the atomic size or ionic radii of tri positive lanthanide ions decrease gradually from La to Lu. Lanthanide contraction is the progressive decrease in size as the atomic number increases.

Consequences of Lanthanide Contraction

The effect of lanthanide contraction will be clearly depicted in the following points:

1. Atomic mass

2. The separation of lanthanides is difficult.

3. Hydroxide

4. The formation is complicated.

5. The d-block elements' ionisation energy

1. Atomic size: The third transition series atom is almost identical in size to the second transition series atom. For e.g., the radius of Zr equals the radius of Hf, and the radius of Nb equals the radius of Ta, and so on.

 2. Difficulty in the separation of lanthanides: Lanthanides' chemical properties are identical since their ionic radii differ just slightly. This makes it difficult to separate elements in their pure state.

3. Effect on the basic strength of hydroxides: The covalent character of the hydroxides increases as the size of lanthanides decreases from La to Lu, and thus their basic strength decreases. As a result, La (OH)3 is the most basic, while Lu (OH)3 is the least basic.

4. Complex formation: The propensity to shape coordinates is due to the smaller size but higher nuclear charge. From La3+ to Lu3+, the number of complexes increases.

5. Electronegativity: From La to Lu, it gets better.

 6. Ionization energy: The nuclear charge attracts electrons much more strongly, so the ionisation energy of 5d elements is much higher than that of 4d and 3d elements. Except for Pt and Au, all elements in the 5d sequence have a filled s-shell.

Ionization Energy is the same for all elements from Hafnium to Rhenium, and it increases with the amount of mutual d-electrons after that, with Iridium and Gold having the highest Ionization Energy.

Case Study:

Mercury – the liquid metal: At room temperature, mercury is the only metal that remains in its liquid form. Mercury's 6s valence electrons are more closely pulled by the nucleus (lanthanide contraction), resulting in less involvement of outer s-electrons in metallic bonding.

 7. Formation of Complex: Lanthanides with a 3+ oxidation state has a higher charge to radius ratio and hence a lower charge to radius ratio. As compared to d-block elements, this decreases the ability of lanthanides to form complexes. They still form complexes with strong chelating agents such as EDTA, -diketones, and oxime, among others. P-complexes are not formed by them.

Electronic Configuration of Lanthanides

Promethium (Pm) with atomic number 61 is the only synthetic radioactive element among the fourteen lanthanides with a terminal electronic configuration of [Xe] 4f1-14 5d 0-16s2. Since the energies of the 4f and 5d electrons are almost identical, the 5d orbital remains empty and the electrons join the 4f orbital.

The exceptions are gadolinium (Z = 64), where the electron enters the 5d orbital due to the presence of a half-filled d-orbital, and lutetium (Z = 71), where the electron enters the 5d orbital due to the presence of a half-filled d-orbital.

Oxidation State of Lanthanides

The oxidation state of all elements in the lanthanide sequence is +3. Some metals (samarium, europium, and ytterbium) were previously thought to have +2 oxidation states. Further research on these metals and their compounds has shown that in solution, all metals in the lanthanide sequence have a +2-oxidation state.

A few metals in the lanthanide sequence have +4 oxidation states on rare occasions. The high stability of empty, half-filled, or completely filled f-subshells is responsible for the uneven distribution of oxidation states among metals.

The oxidation state of lanthanides is affected by the stability of the f-subshell in such a way that the +4-oxidation state of cerium is preferred because it acquires a noble gas configuration, but it reverts to a +3-oxidation state and thus acts as a strong oxidant that can also oxidise water, though the reaction is slow.

The oxides of: display the +4-oxidation state as well.

Praseodymium is the first element in the periodic table (Pr)

2. The element neodymium (Nd)

Terbium is the third element of the periodic table (Tb)

Dysprosium is a kind of dysprosium (Dy)

Europium (atomic number 63) has the electronic configuration [Xe] 4f7 6s2, which means it loses two electrons from the 6s energy level and achieves the extremely stable, half-filled 4f7 configuration, which makes it easy to shape Eu2+ions. Eu2+ then oxidises to the normal lanthanide oxidation state (+3) and forms Eu3+, which acts as a strong reducing agent.

Ytterbium In the Yb2+ state, (atomic number 70) has a totally filled f-orbital and is a good reducing agent for similar reasons.

The existence of an f-subshell has a significant impact on the oxidation state and properties of these metals. New discoveries and advances continue to contribute to the body of knowledge about lanthanides.

Unlike the d-block elements, the energy gap between 4f and 5d orbitals is high, limiting the number of oxidation states.

Why Lanthanide show Variable Oxidation State?

Lanthanides have a wide range of oxidation states. They also reveal oxidation states of +2, +3, and +4. Lanthanides, on the other hand, have the most stable oxidation state of +3. As a result, elements in other states try to lose or gain electrons in order to reach the +3 state. As a result, those ions become powerful reducing or oxidising agents.

Oxidation state in Aqueous Solution

Sm2+, Eu2+, and Yb2+ lose electrons in aqueous solution and become oxidised, making them strong reducing agents. Ce4+, Pr4+, and Tb4+, on the other hand, gain an electron and are strong oxidizers. Only oxides allow for higher oxidation states (+4) of elements. Pr, Nd, Tb, and Dy are some examples.

Chemical Reactivity of Lanthanides

The reactivity of all lanthanides is similar, but it is higher than that of the transition elements. This is due to the outer 5s, 5p, and 5d orbitals protecting unpaired electrons from the inner 4f-orbital.

Except for CeO2, which reacts with hydrogen at 300-400 C to form solid hydrides, they readily tarnish with oxygen and form M2O3 oxides.

Water causes hydrides to decompose. Halides are generated by heating metals or oxides with halogen or ammonium halide. Fluorides are insoluble, while chlorides are liquescent. In water, nitrates, acetates, and sulphates are soluble, but carbonate, phosphate, chromates, and oxalates are not.

Ionization Energy of Lanthanides

Ionization energy is the amount of energy required to detach the valence electron from an atom/ion, and it is proportional to the electron's force of attraction. As a result, the ionisation energy increases as the nuclear charge and electron radii decrease (IE). In addition, the ionisation energy for half-filled and completely filled orbitals would be higher.

The lanthanides' IE is larger than the s-block and smaller than the d-block elements, which they are sandwiched between.

Physical Properties of Lanthanides

1. Density: Since density is defined as the ratio of a substance's mass to its volume, d-block elements will have a higher density than s-block elements. The density pattern in the inner transition sequence will be the inverse of atomic radii, i.e., density will increase as the atomic number increases over time.

Their density is high, ranging from 6.77 to 9.74 g cm-3. It rises as the number of atoms in the nucleus rises.

2. Melting and Boiling Points: Lanthanides have a relatively high melting point, but there is no clear trend in their melting and boiling points.

 3. Magnetic Properties: The interaction of materials with the magnetic field is defined as follows:

1. If repelled, diamagnetic

2. If attracted, paramagnetic

Because of unpaired electrons in orbitals, lanthanide atoms/ions other than f0 and f14 are paramagnetic. As a result, the diamagnetic elements Lu3+, Yb2+, and Ce4+ exist.

The ‘orbital magnetic moment' and the ‘spin magnetic moment' are both influenced by unpaired electrons. The overall magnetic moment is calculated using the orbital angular moment and spin magnetic moment of the electrons.

Μ = √[4S(S+1) +L(L+1)] BM and its unit is Bohr Magneton (BM)
Formation of Coloured Ions

Like the d-block elements, lanthanides ions may have electrons in f-orbitals as well as empty orbitals. When a frequency of light is absorbed, the light emitted has a complementary colour to the absorbed frequency. Inner transition element ions can absorb visible frequency and use it for f-f electron transitions, resulting in visible colour.

Many lanthanide metals have a silvery white colour. In both solid state and aqueous solution, lanthanide ions with a +3-oxidation state are coloured.

The number of unpaired f electrons determines the colour of a cation. Lanthanides with xf electrons are the same colour as elements with (14-x) electrons.

Uses of Lanthanides

1. Metallurgical applications: Some lanthanide material alloys are used as reducing agents in metallurgical processes. Misch metals, for example (Ce- 30 to 35 percent)

2. Ceramic applications: Ce (III) and Ce (IV) oxides are used in glass polishing powders, while Nd and Pr oxides are widely used in glass colouring and standard light filter processing.

3. Lanthanide compounds are used as catalysts in some applications. As an example, cerium phosphate is used as a catalyst in petroleum cracking.

4. Electronic applications: 3Ln2O3.5Fe2O3 ferromagnetic garnets are used in microwave systems.

5. Nuclear uses: These elements, as well as some of their compounds, are used in nuclear power, shielding, and fluxing devices. Some of the essential isotopes used in nuclear technology are Sm – 140, Eu – 153, Gd – 155, Gd – 157, and Dy – 164.

6. Lanthanide oxides may be used as phosphors in fluorescent materials.

7. Ceramic sulphate is an excellent analytical oxidizer.

Properties and Chemical Reactions

The basicity of the Lanthanides is a property that affects how they react with other elements. The basicity of an atom is a test of how easily it can lose electrons. In other words, it refers to a cation's lack of attraction to electrons or anions. Basicity, in simple words, refers to how much of a foundation a species has. The basicity sequence for Lanthanides is as follows:

Tb3+ > Dy3+ > Ho3+ > Er3+ > Tm3+ > Yb3+ > Lu3+ > La3+ > Ce3+ > Pr3+ > Nd3+ > Pm3+ > Sm3+ > Eu3+ > Gd3+ > Tb3+ > Dy3+ > Ho3+ > Er3+ > Tm3+ > Yb3+ > Lu3+

In other terms, as the atomic number increases, the basicity decreases. Differences in basicity can be seen in the solubility of salts and the formation of complex species. The magnetic properties of the Lanthanides are another feature. The fact that each moving electron is a micromagnet determines the magnetic properties of any chemical species. The species are either diamagnetic (no unpaired electrons) or paramagnetic (some unpaired electrons). La3+, Lu3+, Yb2+, and Ce4+ are the diamagnetic ions. The remaining elements have a paramagnetic property.

Metals and their Alloys

When the metals are freshly cut, they have a silvery sheen. They can, however, tarnish quickly in air, especially Ce, La, and Eu. When these elements come into contact with water in the cold, they respond slowly, but when heated, they react rapidly. This is due to the fact that they are electropositive. The reactions of the Lanthanides are as follows:

1. quickly oxidise in moist air

2. easily dissolve in acids

3. At room temperature, the reaction with oxygen is sluggish, but it can ignite at temperatures of 150-200 °C.

4. when heated, react with halogens

5. React with S, H, C, and N when heated

3.2.3 Actinides:

What are Actinides?

The word "actinide sequence" comes from actinium, the first element in the series. The symbol An is used to refer to all of the actinide series elements, which have atomic numbers ranging from 89 to 103 in the periodic table.

Both elements in the actinide sequence are radioactive in nature, and radioactive decay releases a significant amount of energy. The most common naturally occurring actinides on Earth are uranium and thorium, while plutonium is synthesised.

Power reactors and nuclear weapons also use these components. Uranium and thorium are currently used in a variety of applications, while americium is used in the ionisation chambers of modern smoke detectors.

Lanthanides and actinides are shown as two separate rows below the main periodic table in the current periodic table.

The general electronic configuration of actinides is [Rn] 5f1-14 6d0-1 7s2. Here [Rn] is the electronic configuration of the nearest noble gas which is Radium.
Electronic Configuration of Actinides

Actinides are the second sequence of f-block components with the electronic configuration [Rn] 5f1-14 6d 0-17s2. Since the energies of 5f and 6d electrons are similar, electrons join the 5f orbital.

Actinide Contraction

Due to increasing nuclear charge and electrons entering the inner (n-2) f orbital, the atomic size/ ionic radii of tri positive actinides ions decrease gradually from Th to Lw.

Actinide contraction, like lanthanide contraction, is a progressive decrease in size with increasing atomic number. The contraction is larger along the time due to the weak shielding provided by 5f electrons.

Formation of Coloured Ions

Like the d-block elements, actinides like lanthanides ions have electrons in f-orbitals as well as empty orbitals. The f-f electron transition creates a visible colour when a frequency of light is absorbed.

Ionization of Actinides

Since 5f electrons are more easily protected from nuclear charge than 4f electrons, actinides have lower ionisation enthalpies than lanthanides.

Oxidation State of Actinides

Since the energy difference between the 5f, 6 d, and 7s orbitals is smaller in actinides, they have variable oxidation states. Because of the strong shielding of f-electrons, other oxidation states are possible, even though 3+ is the most stable.

The maximum oxidation state rises until the middle of the sequence, then falls, i.e., it rises from +4 for Th to +5, +6 and +7 for Pa, V, and Np, but falls in the following elements.

Oxides

Both actinides produce oxides of varying oxidation states. The most popular oxides are those with the formula M2O3, where M is one of the Actinide elements. The oxidation state of the earliest actinides is proportional to the number of electrons on the outer shell, bringing them closer to the transition metals. In the Actinide series, the +4 condition is more stable than in the Lanthanide series. The different oxides of the Actinide elements are as follows:

(?)-Neptunium is unknown in this oxide state, but scientists assume it does exist.

Formation of Complexes

Because of their smaller size but higher nuclear charge, actinides are stronger complexing agents than lanthanides. They can also form P – complexes.

In the order M4+ > MO22+ > M3+ > MO22+, the degree of complexion decreases.

Chemical Reactivity of Actinides

Actinides are more electropositive and reactive than lanthanides due to their lower ionisation energy. When they come into contact with hot water, they respond. Shape a passive coating by reacting with oxidising agents. Halides and hydrides are formed. Actinides are strong reducers.

Physical Properties of Actinides

Density of Actinides: Except for thorium and americium, both actinides have extremely high densities.

 Melting and Boiling Points of Actinides: Actinides, like lanthanides, have relatively high melting points, but there is no clear trend in the melting and boiling points of lanthanides.

 Magnetic Properties of Actinides: In fact, all actinides are paramagnetic, which is determined by the presence of unpaired electrons. Because of the shielding of 5f electrons, the orbital angular moment is quenched, and the measured magnetic moment is less than the estimated.

Key takeaway:

1. Lanthanides are a group of 15 chemical elements whose atomic numbers range from 57 to 71.

2. In the 5d shell, all of these elements have one valence electron.

3. The elements have properties in common with the group's first member, lanthanum.

4. Lanthanides are silver-colored reactive metals.

5. The actinides are elements 89 to 103 that gradually fill their 5f sublevel. Actinides are common metals with properties of both the d- and f-block elements, as well as being radioactive.

3.3 Lanthanide contraction, separation of lanthanides

3.3.1 Lanthanide contraction:

Introduction

All 14 elements in the Lanthanide sequence are affected by the Lanthanide Contraction. Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), and Lutetium (Yb) are members of this sequence (Lu). According to the Lanthanide Contraction, the atomic radius of these elements decreases as the atomic number increases. A periodic table can be used to compare the elements Ce and Nd. The atomic number of Ce is 58, and the atomic number of Nd is 60. Which one's atomic radius would be smaller? Because of its greater atomic number, Nd would.

The graph shows the atomic radius decreasing as the atomic number is increasing, Lanthanide Contraction.

Shielding and its Effects on Atomic Radius

The Lanthanide Contraction is caused by the 4f electrons' weak shielding effect. The shielding effect is a mechanism in which the inner-shell electrons protect the outer-shell electrons from the effects of nuclear charge. If the shielding isn't as strong, the positively charged nucleus attracts the electrons more, reducing the atomic radius as the atomic number rises. The s orbital has the most shielding, the f orbital has the least, and the p and d orbitals are in the centre, with p being greater than d.

When comparing elements with f electrons and those without f electrons in the d block orbital, the Lanthanide Contraction can be observed. Pd and Pt are two examples of such elements. Pd has 4d electrons, while Pt has 5d and 4f. The atomic radius of these two elements is almost identical. Lanthanide Contraction and Shielding are to blame for this. Pt should have a much greater radius when more electrons and protons are added, but it doesn't because the 4f electrons are weak at shielding. Where the shielding is inadequate, there will be a higher nuclear charge, which will draw the electrons in closer together, resulting in a radius that is smaller than predicted.

Row 1 of Periodic Table D Block Row 2 Row 3

The graphs show the atomic radii of the transition metals' first three rows. We may apply the same concept to entire rows and columns as we did with the elements Pd and Pt. When we compare Row 1 and Row 2, we can see that the atomic radii of the elements vary significantly, but when we compare Row 2 and Row 3, the atomic radii do not differ significantly. The atomic radii of elements 23 and 41, which are in the same column of the periodic table, differ greatly (atomic radii rise from Row 1 to Row 2), but elements 41 and 73, which are also in the same column, differ only slightly. The introduction of 4f electrons in Row 3 is due to this. We would expect the elements in Row 3 to follow the same pattern as in Rows 1 and 2 (a significant increase in atomic radii), but this is not the case. This is due to the fact that the 4f orbitals aren't very good at shielding.

D Block Contraction (Scandide Contraction)

The atomic radius pattern that the d block elements (Transition metals) experience is defined by the d block contraction, also known as the Scandide Contraction. When travelling around the periodic table, the atomic radius typically decreases dramatically. If we pass from left to right around the periodic table, the atomic radius of transition metals with D electrons decreases significantly. This is due to the fact that they have the same number of s electrons but vary only in the number of d electrons. These d electrons are in the penultimate shell of an inner shell, and electrons are being added to it; no new shell is being formed. Since the d electrons are ineffective at protecting the nuclear charge, the atomic radius does not change significantly when more electrons are introduced. It's almost as if the D electrons aren't being applied.

Effects on Ionization Energy and Properties

The ionisation energy increases as the number of protons increases and the atomic radius decreases. This is due to a more positively charged nucleus and a stronger nucleus tug on electrons. An increased effective nuclear charge causes a stronger pull. The nucleus has a more positive charge than the electron's negative charge, resulting in effective nuclear charge (net positive charge). The density, melting point, and hardness of the Lanthanide Series increase from left to right. The Lanthanide Contraction facilitates Lanthanide chemical separation. While the Lanthanide Contraction makes it easier to separate Lanthanides chemically, it makes it more difficult to separate elements in the sequence.

3.3.2 Separation of lanthanides:

This is the most important, fastest, and most reliable general method for separating and purifying the lanthanide elements. A lanthanide ion solution is passed through a Dowex-50 synthetic ion-exchange resin column. The functional group – SO3H – is found in this sulphonated polystyrene. The Ln3+ ions bind to the resin and take the position of the hydrogen atom in – SO3H.

3H(resin) + Ln3+(aq) (s) 3H+ Ln(resin)3(s) (aq)

The formed H+ ions are washed through the column. The metal ions are then selectively eluted, that is, washed off the column. A complexing agent, such as a buffered citric acid/ammonium citrate solution or a dilute solution of (NH4)3(H. EDTA) at pH 8, is used as the eluting agent. Consider the case of citrate. An equilibrium has been established;

3H+ + Ln(resin)3 (citrate)

3 – 3H(resin) + Ln 3 – 3H(resin) + Ln 3 – 3H (re (citrate)

Ln3+ ions are separated from the resin and form the citrate complex as the citrate solution flows down the column. The Ln3+ ions return to the resin a little further down the column. The metal ions form complexes with the resin and the citrate solution many times as the citrate solution runs down the column. The metal ion gradually makes its way down the column, eventually emerging as the citrate complex at the bottom. Smaller lanthanide ions, such as Lu3+, form stronger complexes with the citrate ions, spend more time in solution and less time on the column, and thus are eluted first. Different metal ions break into bands that travel down the column. Atomic fluorescence can be used to monitor the progress of the bands spectroscopically. An automated fraction collection in separated collects the solution that exits the column. Metals can be precipitated as insoluble oxalates, which can then be heated to form oxides.

Many separations or crystallizations are carried out in the chromatographic phase, but the separation is carried out on a single column. The elements can be obtained 99.9% pure in one pass using a long ion-exchange column.

Key takeaway:

1. The Lanthanide Contraction is caused by the 4f electrons' weak shielding effect. Since the atomic radius decreases as the atomic number increases, Gd. Since it has a higher atomic number, Yb is preferred. Since the elements in Row 3 have four electrons, they are referred to as 4f elements.

2. The lanthanide contraction is a larger-than-expected decrease in the ionic radii of the elements in the lanthanide sequence from atomic number 57, lanthanum, to atomic number 71, lutetium, resulting in smaller-than-expected ionic radii for the elements following 72, hafnium.

3. From La (OH)3 to Lu (OH)3, the basic strength of hydroxides decreases. The size of M3+ ions decrease as a result of lanthanoid contraction, and the covalent character of the M – OH bond increases.

3.4 General features of actinoids, separation of Np, Pm, Am, from U

3.4.1 General features of actinoids:

1. Because of their volatility, they are all radioactive.

2. The majority is made synthetically by particle accelerators that produce nuclear reactions and is short-lived.

3. Since they have an atomic number greater than 83, they are both unstable and reactive (nuclear stability).

4. In metallic form, they all have a silvery or silvery-white lustre.

5. They're all capable of forming stable complexes with ligands including chloride, sulphate, carbonate, and acetate.

6. Several actinides can be found in seawater or minerals in nature.

They can undergo nuclear reactions, for example.

8. They are dangerous to treat because of radioactivity emission, toxicity, pyrophoricity, and nuclear criticality.

a. Radioactivity Emission: The elements emit alpha, beta, and gamma radiation, as well as neutrons created by spontaneous fissions or boron, beryllium, and fluorine reacting with alpha-particles.

b. Toxicity: They are considered poisonous elements due to their radioactive and heavy metal properties.

c. Pyrophoricity: Many actinide metals, hydrides, carbides, alloys, and other compounds can spontaneously ignite in a finely divided state at room temperature, resulting in fires and the spread of radioactive contaminates.

d. Nuclear Criticality: When fissionable materials are mixed, a chain reaction may occur, resulting in lethal doses of radioactivity, but this is dependent on chemical structure, isotopic composition, geometry, and the size of the surrounding environment, among other factors.

9. When radioactive actinides interact with various types of phosphors, light pulses are produced.

3.4.2 Separation of Np, PU, Am, from U:

Introduction

Separating uranium and transuranium elements has been studied using a variety of methods. Literature [1-6] contains analytical methods for determining Am, Pu, Np, and U from a nitric acid solution using an anion exchange resin. N. Shinohara and N. Kohno [3] studied the chemical separation of Np by an anion exchange method from a neptunium oxide material and the analytical method for Np and Am in irradiated fuels based on ion exchange and oxidation. Chilton [1] reported on the isolation of plutonium in chloride media by an anion exchange resin, and N. Shinohara and N. Kohno [3] reported on the chemical separation of N While several researchers have looked into separating atransuranium elements from nitric acid solutions using an anion exchange resin, findings in hydrochloric acid solutions are still restricted. The effects of mutual separation and purification of the Am, Pu, Np, and U in a chloride media are briefly described in this paper.

3.4.3 Experimental:

Preparation of anion exchange resin column

A plastic funnel, a 60 mm (L.) by 4.7 mm (I.D.) plastic syringe tube, and a one-way plastic stopcock made up the column, which was an integral assembly. In the bottom and upper sections of the resin bed, a disc plug was used instead of glass wool. Bio-rad AG 1x4 (analytical grade, 100-200 mesh chloride form) was soaked in 1M HCl for 24 hours and then washed with distilled water until the wash was neutral. The column was carefully lined with washed resin. The resin column was washed with 10ml of 9M HCl 0.1M HNO3 before use.

Tracer solution

Nuclides 241Am, 239Pu, 237Np, and 233U were used to make the tracer solution. In 10ml of 0.1M HCl, 241Am, 239Pu, and 237Np each had about 80 Bq of operation, while 233U had far more than 80 Bq. 1 ml of 1M NH2OH-HCl was applied to the tracer solution and dried under an infrared lamp before being dissolved with 2 ml of 9M HCl-0.1M HNO3 to regulate the oxidation state of the nuclides in the tracer solution. Finally, we determined the oxidation states of Am (III), Pu (IV), Np (IV), and U(VI).

Column operations procedure

Resin is applied to the plastic column as a slurry in water before a resin bed of about 5cm in length (ca. 0.8 ml) is created. The column is then pre-treated with 10ml of 9M HCl0.1M HNO3 and 0.5ml of the tracer solution before being put in a column supporter. The flow rate is held to about 0.42 ml/min. 3ml of 9M HCl0.1M HNO3 is applied to the top of the resin bed after the sample has passed through. Am is eluted by passing it through 6ml of 9M HCl-0.1M HNO3 after the tracer solution has passed into the bed. For examination, the effluent is collected in a plastic vial. 9ml of 9M HCl-0.1M HI is passed through the resin bed to elute Pu. In a plastic vial, the effluent is stored. By passing 9ml of 4M HCl solution through the resin bed, Np is extracted. In a plastic vial, the effluent was stored. Finally, 5ml of 0.1M HCl is passed through the resin bed to extract the uranium. In a plastic vial, the effluent was stored. Alpha spectrometry or LSC measurements were used to test all of the effluents that were collected in plastic vials.

Electrodeposition

A constant power supply was used to power an electrodeposition device that included a deposition cell, Pt electrode, planchet, and cell holder. The samples were dried with an infrared lamp before being electrodeposited with a 0.1M NaHSO4-0.53M Na2SO4 buffer solution. In a 0.1M NaHSO4-0.53 MNa2 SO4 buffer solution, the best electrodeposition conditions were 1200 mA and 60 minutes. With alpha spectrometry, this approach was used to determine the 241Am, 239Pu, 237Np, and 233U.

LSC measurements and alpha spectrometry The alpha spectra of 241Am, 239Pu, 237Np, and 233U were analysed using a multi-channel pulse height analysis device with a 300 mm2 silicon surface-barrier alpha counter (EG&G/ ORTEC Co., Alpha-King Module). The cumulative activity of the elution samples was measured using a liquid scintillation analyzer (Packard model 2500TR/AB).

3.4.4 Results and discussion:

Principle concept of sequential separation of Am, Pu, Np and U in chloride media

Figures 1 and 2 demonstrate the distribution coefficients of actinides on anion exchange resins in an HCl solution, as well as the flow sheet for the separation of Am, Pu, Np, and U using an anion exchange chromatographic technique.

Elution profile of Am, Pu, Np and U

In the anion exchange separation column, the elution profiles of Am (III), Pu (III), Np (IV), and U(VI) are shown in Fig. 3. As a stock solution, 10ml of 9M HCl-0.1M HNO3 was mixed with 241Am, 239Pu, 237Np, and 233U. An anion exchange resin column was pre-treated with a 9M HCl-0.1M HNO3 solution until a 0.5ml aliquot of the stock solution was applied. After the sample had drained into the resin bed, an elution with 9ml of 9M HCl 0.1M HNO3 was performed, which eliminated the Am (III), but left Pu (IV), Np (IV), and U(VI) adsorbed in the anion exchange resin column.

Fig.  Distribution coefficients of actinides on anion exchange resins in HCl solution

Fig. Flow sheet for separation Am Pu, Np, and U

Fig. 3 Elution profile of Am, Pu, Np and U on a column packed with Bio-rad (100-200 mesh)

A 9ml 9M HCl-0.1M HI solution was used to extract the Plutonium. A 9ml 4M HCl solution was used to extract Pu (IV), and a 5ml 0.1M HCl solution was used to remove uranium. The eluent was applied all at once, 0.5ml at a time. An additional 0.5 ml of eluent is applied after the eluent has passed through the bed and collected in a scintillation plastic vial. The LSC looked at the eluents. The HCl concentration in the Pu elution should not exceed 10 M; otherwise, a partial reduction of U(VI) by iodide will occur, contaminating the Np fraction with U.

Mutual separation of Am, Pu, Np and U in HCl

The anion exchange chromatographic method was used to separate 241Am, 239Pu, 237Np, and 233U according to the flow sheet in Fig. 2. The mutual separation protocol is identical to the elution profile of Am, Pu, Np, and U. The plutonium and neptunium fractions need more repeated purifications, as defined in the mutual separation procedure. Figures 4(A), 4(B), 4(C), and 4(D) demonstrate the alpha spectra of the americium fraction, plutonium fraction, neptunium fraction, and uranium fraction, respectively.

Fig. Alpha spectra of Am fraction(A), Pu fraction(B), Np fraction (C) and U fraction

(D)

Conclusion

This research could be used to develop a quick method for separating actinide elements, especially Am, Pu, Np, and U. The developed protocol was used to analyse a nuclear waste sample that contained the nuclides Am, Pu, Np, and U. The purification of actinide elements can also be accomplished using this process.

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