TS Inter 2nd Year Chemistry Notes Chapter 7 d and f Block Elements & Coordination Compounds

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TS Inter 2nd Year Chemistry Notes 7th Lesson d and f Block Elements & Coordination Compounds

→ Elements with partially filled d-orbitals in the penultimate shell in their atoms or in the ions in principal oxidation state are called transition elements.

• 3d series contain Sc (21) to Zn (30).
• 4d series contain Y(39) to Cd (48).
• 5d series contain La (57) to Hg (80).
• The fourth row of 6d is still incomplete.

→ General electronic configuration of d-block elements is (n – 1) d^1-10 ns^1-2.

→ Transition elements exhibit different oxidation states, formation of aqueous coloured ions, and ability to form complex compounds with a variety of ligands.

→ Transition metals have high melting points. The high melting points are attributed to the involvementtsf greater number of electrons in the interatomic metallic bonding.

→ As shielding effect of d electrons is poor, net electrostatic attraction between the nuclear charge and the outermost electron increases and the ionic radius decreases.

→ There is a gradual size decrease from La (57) to Lu (71) which is known as lanthanoid contraction.

→ Transition elements show variable oxidation states due to involvement of ns² electrons and some or all electrons in (n – 1) d ele¬ctrons as the energy difference between ns and (n – 1) d sublevels is less.

→ Paramagnetism arises from the presence of unpaired electrons. The magnetic moment is determined by spin only formula.
μ = \(\sqrt{n(n+2)}\)
where n is the no. of unpaired electrons and μ is the magnetic moment in Bohr magneton.

→ The colour exhibited by transition metal ions is due to d-d transitions.

→ Transition metal ions form complex compounds. This is due to the comparatively smaller sizes of the metal ions, their high ionic charges and the availability of d-orbi- tals for bond formation.

→ Zn++ is colourless due to non-availability of unpaired d-electrons.

→ Tetrahedral complexes do not show geometrical isomerism because the relative positions of unidentate ligands attached to central metal atom are the same with respect to each other.

→ When (n – 1) d orbitals participate in hybridisation, inner orbital complex form. They are called low spin complexes. When d- orbitals of outer shell participate, outer orbital complexes form. They are high spin complexes.

→ Valence bond explains the formation of complexes. Central metal ion makes available vacant d-orbitals. Ligands donate electrons to form coordinate covalent bonds.
(n – 1) d, ns, np or ns, np, nd orbitals hybridise to form of set of equivalent orbitals of definite geometry such as octahedral, square planar and so on. These hybridised orbitals overlap with ligand orbitals that can donate electron pairs for bonding.

→ In the presence of ligands, d-orbitals are split into two groups.

→ Ligands which cause large splitting are called strong field ligands.

→ Ligands which cause low value for splitting are called weak field ligands.

→ The metal-carbon bond in metal carbonyls possess both σ and π character. The M – C σ bond is formed by the donation of the pair of electrons on the carbonyl carbon into a vacant orbital of the metal. The M – C π bond is formed by the donation of a pair of electrons from a filled d-orbital of metal into the vacant antibonding π* orbital of carbon monoxide.

→ The instability constant is the reciprocal of formation constant

→ Hardness of water is estimated using simple titration with Na₂EDTA. The Ca²⁺ and Mg²⁺ ions form stable complexes with EDTA.

→ Coordination compounds are used as catalysts for many industrial processes.
Ex : Rhodium complex [(Ph₃P)₃ RhCl], is used for hydrogenation of alkenes: