The d- and f - Block Elements

d-Block

d-Block

• Elements whose last filled electron enters into a d-orbital in a pen-ultimate shell of the atom are called d-block elements

• The d-block of the periodic table contains the elements of the groups 3-12

• d-block elements can be classified into four series:

  1. 3d series (first transition series):

     ₂₁Sc -> ₃₀Zn (10 elements)

  2. 4d series (second transition series):

     ₃₉Y -> ₄₈Cd (10 elements)

  3. 5d series (third transition series):

     ₅₇La -> ₈₀Hg (10 elements)

  4. 6d series (fourth transition series):

     ₈₉Ac -> ₁₁₂Cn (10 elements)

d-block elements are

• Metallic elements; have a higher metallic character than s-block elements

• Metals:

  • Have a very hard crystalline structure

  • High melting and boiling point

• Mostly paramagnetic

• Electro +ve with low ionisation energy

• Show variable oxidation state

• Show the highest catalytic properties and can form complex compounds easily

Electronic Configurations of the d-Block Elements

• General config: (n-1)d^1-10ns^1-2

Special Cases:

• Pd config: 4d¹⁰5s^o

• Cr config: [Ar]3d⁵4s¹ and Cu config: [Ar]3d¹⁰4s¹

  This is because:

  • Half and completely-filled sets of orbitals are relatively more stable

  • The energy gap between the two sets (3d and 4s) of orbitals is small enough to prevent electrons from entering the 3d orbitals

d-block elements as Transition elements

• Elements with partially or incompletely filled d-orbital in their ground state or any one of its stable oxidation state

• Zn, Cd and Hg are not considered transition elements since they have completely filled d-orbital in their ground and stable oxidation state

  Their ground state config looks like this: (n-1)d¹⁰ns²

  Even in their +2 common oxidation state, they are completely filled

• Cu and Ag have completely filled d-orbitals in their ground state but are transition elements in their stable oxidation state of +2 where they have a d⁹ configuration

Identifying Group and Period of a d-block Element based on Config

For any d-block element, (n-1)d^xns^y

• group = x+y

• period = n

Atomic Radii

• The equilibrium distance between the centre of the nucleus and the outermost energy level

• In periods: decreases

  due to an increase in nuclear charge

• In groups: increases

• Towards the end of a period, the elements show a very small difference in atomic radii and show a gradual increase in size due electron pairing effect of d-orbitals and an increased shielding effect which counterbalances the increase in nuclear charge

• Effective nuclear charge Z* = Z (nuclear charge) - S (shielding effect) see note for example

Lanthanoid Contraction

• Among d-block elements 4d and 5d series elements show similar atomic radii and similar physical properties due to lanthanoid contraction

  Eg: Zr and Hf have similar atomic radii and similar physical properties

• A regular decrease in atomic radii of lanthanoid series elements with increase in atomic number is known as lanthanoid contraction

• This is due to poor shielding of 4f electrons

Ionic Radii

Ionic size decreases with increase in oxidation state

Enthalpy of Atomisation

• The energy required to form one mole of atoms from a molecule in standard elemental form

• Depends on:

  • Strength of metallic bond which in turn depends on,

  • Number of unpaired electrons

  • E_oA ∝ Metallic Bond ∝ Number of unpaired electrons

• As we move across a period, the enthalpy of atomisation increases and then decreases

• In the 3d series, Zinc has the lowest enthalpy of atomisation since it has a filled d¹⁰ configuration and hence has a lower metallic bond strength

Personal Note: the graph is not in the order of each series

Ionisation Enthalpy/Energy/Potential

• The energy required to remove the most loosely bound electron from the outermost energy level of an isolated, neutral and gaseous atom.

• Factors affecting I.E:

  • I.E ∝ 1/Atomic Size

  • I.E ∝ Nuclear Charge

  • I.E ∝ 1/Shielding Effect

  • I.E ∝ 1/Complexity of Shape

  • I.E ∝ Stability of Configuration

• Across periods: increases

• Across groups: decreases

• For a given atom, the first ionisation energy will be less than the second, less than the third and so on

  I.E.1 < I.E.2 < I.E.3 < ...

• When an electron is removed from a stable configuration, greater I.E. is used

• When an electron is removed to attain a stable configuration, less I.E. is used

• In d-block elements, the possible stable configurations are:

  • d⁰ → Noble gas config

  • d³ → Half filled t_2g config

  • d⁵ → Half filled d-config

  • d⁶ → Completely filled t_2g config

  • d¹⁰ → Completely filled d-config

• In 3d series, element with

  • lowest I.E → Sc

  • highest I.E → Zn

see note for examples of higher I.E₂, I.E_3, etc.

Melting and Boiling Points

• The melting and boiling points of an element depend on the strength of the metallic bond in its metallic crystal lattices

• Across periods: increases then decreases

• Across groups: generally increases

• Mn has lesser M.P and B.P when compared to its neighbours since it has a half-filled d⁵ configuration which is not involved in the formation of a metallic bond. Due to the weak metallic bond, it has a weak M.P and B.P

• Zn has a low M.P and B.P among 3d series elements because it has a stable completely filled d¹⁰ configuration which is not involved in the formation of a metallic bond. Due to the weak metallic bond, it has a weak M.P and B.P

Which element has the highest M.P in 3d series and entire d-block?

• In the 3d series, Cr has the highest melting point because it has the highest number of unpaired electrons (3d⁵4s¹ config) and therefore has a greater metallic bond strength

• Tungsten (W) has highest M.P in d-block

Oxidation State

• d-block elements can show variable oxidation state

  due to the small energy difference between ns and (n-1)d orbitals

• Most common O.S is +2

• Across periods: increases then decreases

• Can form compounds involving the valence electrons as well as the inner d-orbitals

• The acidic character of compounds increases with an increase in O.S

• Mn can combine with 7 F in its highest O.S but can combine only with 4 O in higher O.S

• O.S ∝ Covalent character

Sc does now show +2 O.S

Sc only has +3 O.S

Sc does not show variable O.S

Why?

Sc has a 3d¹4s² configuration and by losing 3 electrons it gains noble gas configuration

Mn has the maximum number of O.S. Why?

Mn has a 3d⁵4s² configuration. Hence it can show an oxidation state ranging from +2 to +7

Zn has only +2 O.S. Why?

Zn has 3d¹⁰4s² and by losing 2 electrons it gains completely filled d¹⁰ configuration

Cu is the only element in 3d series with +1 O.S. Why?

Cu has a configuration [Ar]3d¹⁰4s¹ and by losing 1 electron it gains completely filled d¹⁰ configuration

Elements of d-block preferentially form fluorides and oxides in their higher O.S. Why?

Due to small size and high electro-negativity of O and F

Special Elements

• Highest O.S: Osmium (OS) +8 O.S

• Maximum number of O.S: Mn (+2 - +7)

Electrode Potential

• Across periods: increases due to an increase in nuclear charge and decrease in atomic size

• Atomisation enthalpy increases, ionisation enthalpy increases, hydration enthalpy decreases

Cu has a +ve electrode potential. Why?

The high transformation energy from Cu_(s) to Cu²⁺_(aq) is not balanced by hydration enthalpy

The electrode potential of Nickel is more negative than expected. Why?

Nickel has relatively higher hydration enthalpy or more negative hydration enthalpy

Mn has a more negative electrode potential value than expected. Why?

Due to presence of stable d-5 configuration after losing electrons (due to very low IE2)

Zn has more negative electrode potential value than expected. Why?

Due to presence of a completely filled stable d¹⁰ configuration after losing 2 electrons

Oxidising and Reducing Power

Oxidation /Reducing Agent - Loses/Removes Electron

Oxidising Agent/Reduction - Gains Electron

examples in note

• d-block elements can act as both oxidising and reducing agents in their combined forms

• Any species which gains electrons to attain a stable configuration is a very good oxidising agent. Eg: Mn³⁺

• Any species which loses electrons to attain a stable configuration is a very good reducing agent. Eg: Fe²⁺

Magnetic Properties

• Mostly paramagnetic due to the presence of unpaired electron

• Only Sc and Zn are diamagnetic due to no unpaired electrons

• Magnetic moment, μ = √n(n+2) B.M

  n => number of unpaired electrons

  B.M => Bohrn magneton

  • n=1, 1.7 B.M

  • n=2, 2.8 B.M

  • n=3, 3.8 B.M

  • n=4, 4.9 B.M

  • n=5, 5.9 B.M

Formation of Ions

• Most of the d-block elements form coloured ions in their compounds due to the presence of unpaired electrons as they take part in d-d transition

• Few ions of d-block are colourless due to the absence of unpaired electrons as no d-d transition takes place. Eg: Cu⁺, Sc³⁺, Ti⁴⁺, Zn²⁺

• Red-orange colours are typically observed with ions that have a higher number of unpaired electrons.

• Blue and violet colours are typically observed with ions that have a lower number of unpaired electrons

black or white is considered colourless

Catalytic Properties

d-block elements can act as a very good catalyst. Due to presence of more vacant d-orbitals, they show variable oxidation state and can form intermediate complex easily in turn reducing the activation energy of the reaction

Formation of Interstitial Compounds

• Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals.

• They are usually non-stoichiometric and are neither typically ionic nor covalent,

• The principal physical and chemical characteristics of these compounds are as follows:

  • They have high melting points, higher than those of pure metals.

  • They are very hard, some borides approach diamonds in hardness

  • They retain metallic conductivity

  • They are chemically inert

Alloy Formation

• A homogenous mixture of a metal-metal/metal-non-metal

• d-block elements can form alloys easily due to similar atomic radii

• These elements can replace one another in metallic crystal lattices due to similar size

• Eg: Bronze (Copper and Tin), Brass (Copper and Zinc)

Oxides and Oxoanions of Metals

not important

• High oxidation states oxide are acidic

  Ex: CrO₃, Mn₂O₇

  remember as Higher - HCl (Acidic)

• Lower oxidation state oxides are basic

  Ex: MnO, Mn₂O₃, CrO

• Scandium does not form metal oxide

Important Compounds of d-block

• Potassium dichromate (K₂Cr₂O₇)

• Potassium permanganate (KMnO₄)

Preparation of Potassium dichromate

chromite ore (Cr₂O₄^2-) → chromate (CrO₄^2-) → dichromate (Cr₂O₇^2-)

1. Convert chromite ore to sodium chromate (Oxidation of ore in sodium carbonate)

   4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ → 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂

   Sodium chromate is filtered since it has impurities

2. Convert sodium chromate to sodium dichromate (Acidification by H₂SO₄)

   2Na₂CrO₄ + H₂SO₄ → Na₂Cr₂O₇ + Na₂SO₄ + H₂O

3. Convert sodium dichromate to potassium dichromate (Displace with KCl)

   Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl

Structures of Chromate and Dichromate

• Ditetrahedral Geometry

• Red orange crystal

Properties of Potassium Dichromate

• Very strong oxidising agent in acidic medium

• It can oxidise iodide

  • I⁻ → I₂

  • Fe²⁺ → Fe³⁺

  • Sn²⁺ → Sn⁴⁺

  • S^2- → S

  • NO₂^- → NO₃^-

  • SO₃^2- → SO₄^2-

• Can form interconvertible aqueous solutions based on the pH of the solution

  • In acidic medium:

    CrO₄^2- (yellow) → [H⁺] Cr₂O₇^2- (orange)

  • In basic medium:

    Cr₂O₇^2- (red-orange) → [OH^-] CrO₄^2- (yellow)

• Has a greater solubility, used in a primary standard solution in volumetric analysis

• It is an industrially used chemical oxidant used in the preparation of azo compounds and in the leather industries

• Used in chromyl chloride test for confirmation of chloride ion in inorganic compounds

Preparation of Potassium Permanganate

1. Pyrolusite ore to Potassium Manganate

   2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

2. Potassium Manganate to Potassium Permanganate (Disproportionation reaction)

   3K₂MnO₄ + 4H⁺ → 2KMnO₄ + MnO₂ + 2H₂O

Properties of Potassium Permanganate

• Dark purple crystal and comparatively less soluble in water

• It is purple due to the metal-ligand electron transition

• At higher temperatures (513K), it decomposes to produce potassium manganate and magnesium dioxide

  2KMnO₄ → [Δ, 513K] K₂MnO₄ + MnO₂ + O₂

• It is diamagnetic due to the absence of an unpaired electron

• It is a very strong oxidising agent in acidic as well as alkaline medium. It can oxidise:

  • In acidic:

    • I⁻ → I₂ (X⁻ → X₂)

    • Fe²⁺ → Fe³⁺

    • S^2- → S

    • NO₂^- → NO₃^-

    • SO₃^2- → SO₄^2-

    • C₂O₄^2- → CO₂

  • In basic:

    • I⁻ → IO₃^- (X⁻ → XO₃^-)

    • Mn²⁺ → MnO₂

    • S₂O₃^2- → SO₄^2-

f-Block

• Elements whose last electron enters the outermost f-orbital

• Two rows of high-density elements are embedded within the third group and placed at the bottom of the periodic table. These are called f-block elements.

• General config (n−2)f¹⁻¹⁴(n−1)d⁰⁻¹ns²

• Lanthanoids:

  ₅₈Ce → ₇₁Lu (14 elements)

• Actinoids:

  ₉₀Th → ₁₀₃Lr (14 elements)

Consequences of Lanthanoid Contraction

• 4d and 5d series show similar atomic radii and physical properties

• It’s difficult to separate lanthanoids

• The basic character of lanthanide hydroxides decreases from lanthanum (La) to lutetium (Lu)

Oxidation State of Lanthanoids

• Common O.S → +3

• Ce → +4

• Eu, Yb → +2

General Characteristics of Lanthanoids

• Silvery white soft metals

• Tarnish rapidly in air

• Hardness increases with increasing atomic number, Samarium being steel hard.

• Melting points range between 1000 to 1200 K but Samarium melts at 1623 K.

• Typical metallic structure

• Good conductors of heat and electricity

Actinoids

• Radioactive elements

• Earlier members have relatively long half-livers, the latter ones have half-life values ranging from a day to 3 minutes

• Actinoid contraction is the overall decrease in atomic and ionic radii with increase in atomic number of actinoids due to poor shielding effect of f-electrons

• Show a greater range of oxidation states due to very less energy difference between 5f, 6d and 7s orbitals

• Most common oxidation state is +3

• Highly reactive metals especially when finely divided

Differentiate between Lanthanoids and Actinoids