//M2//QN1//SUB//DL0

Silver atom has completely filled d-orbitals (4d 10) in its ground state. How can you say that it is a transition element?

//X

Silver (Z = 47) can exhibit +2 oxidation state where in it will have incompletely filled d-orbitals (4d), hence a transition element.
47Ag : [Kr] 4d 10 5s 1
Ag2+: [Kr] 4d 9

//M2//QN2//SUB//DL0

In the series Sc (Z = 21) to Zn (Z = 30), the enthalpy of atomization of zinc is the lowest, i.e., 126 kJ mol-1. Why?

//X

In the formation of metallic bonds, no electrons from 3d-orbitals are involved in case of zinc, while in all other metals of the 3d series, electrons from the d-orbitals are always involved in the formation of metallic bonds.

//M0//QN3//SUB//DL0

Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?

//X

Manganese (25Mn) shows largest number of oxidation states because it has maximum number of unpaired electrons.

//M3//QN4//SUB//DL0//EQ

The E°(M2+/M) value for copper is positive (+0.34 V). What is possibly the reason for this? (Hint: consider its high D aH° and low D hydH°)

//X

The E°(M 2+/M) value of a metal depends on the energy changes involved in the following:
(1) Sublimation: The energy required for converting one mole of an atom from the solid state to the gaseous state.
Cu(s) → Cu(g) ∆sH° or ∆aH° = 339 kJ Mol–1
(2) Ionization: The energy required to take out electrons from one mole of atoms in the gaseous state.
Cu(g) → + 2e– ∆iH° = 2703 kJ Mol–1
(3) Hydration: The energy released when one mole of ions are hydrated.
∆hydH° = –2121 kJ Mol–1
E°Cu 2+/Cu = ∆aH° + ∆iH° + ∆hydH°
= 339 + 2703 – 2121
= 1921 kJ Mol–1
Total value of all the enthalpies is positive so reaction is endothermic so E°Cu+2/Cu is positive.

//M2//QN5//SUB//DL0

How would you account for the irregular variation of ionization enthalpies (first and second) in the first series of the transition elements?

//X

Irregular variation of ionization enthalpies is mainly attributed to varying degree of stability of different 3d-configurations (e.g., d 0, d 5, d 10 are exceptionally stable).

//M2//QN6//SUB//DL0

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

//X

Because of small size and high electronegativity oxygen or fluorine can oxidise the metal to its highest oxidation state.

//M2//QN7//SUB//DL0

Which is a stronger reducing agent Cr2+ or Fe2+ and why?

//X

Cr2+ is stronger reducing agent than Fe2+.
Reason: d 4 → d 3 occurs in case of Cr2+ to Cr3+.
But d 6 → d 5 occurs in case of Fe2+ to Fe3+.
In a medium (like water) d 3 is more stable as compared to d 5 (see CFSE).

//M2//QN8//SUB//DL0//EQ

Calculate the 'spin only' magnetic moment of M2+(aq) ion (Z = 27).

//X

Z = 27
µ =
=
=
= 3.87 B.M
[Ar] 3d 7 4s 2
\ M2+ = [Ar] 3d 7
3d 7 =
i.e., 3 unpaired electrons
\ n = 3

//M2//QN9//SUB//DL0

Explain why Cu+ ion is not stable in aqueous solutions?

//X

Cu+ in aqueous solution undergoes disproportionation, i.e., 2Cu+(aq) → Cu2+(aq) + Cu(s)
The E° value for this is favourable.

//M2//QN10//SUB//DL0

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

//X

The 5ƒ electrons are more effectively shielded from nuclear charge. In other words the 5ƒ electrons themselves provide poor shielding from element to element in the series.