Ques. 1AIPMT 2003
The basic character of the transition metal monoxides follows the order (Atomic nos. Ti = 22, V = 23, Cr = 24, Fe = 26)
- VO > CrO > TiO > FeO
- CrO > VO > FeO > TiO
- TiO > FeO > VO > CrO
- TiO > VO > CrO > FeO
Answer
(4) TiO > VO > CrO > FeO
Solution
In all four monoxides the metal is in the same +2 oxidation state.
Across the 3d series (Ti V Cr Fe) the nuclear charge increases, so the M2+ ion becomes smaller and its ionisation enthalpy increases.
The M-O bond therefore becomes more covalent and the oxide less basic.
∴ Basic character: TiO > VO > CrO > FeO
Answer: (4)