Question

Give reason (one each) for the following:
a) Transition metals are good catalytic agent
b) Second ionisation enthalpy of copper is very high
c) The spin only magnetic moment of $S{c}^{3+}$ is zero $(Z=21)$

Answer 1

a) Transition metals are good catalytic agent.
Due to presence of variable oxidation states, transition metals form unstable intermediates. They provide large surface area for reactants to be adsorbed and bring them closer to one another for the reaction to occur.
b) Second ionisation enthalpy of copper is very high.
The electronic configuration of $copper$ is $\left[Ar\right]3d^{10}4s^1$
It loses one electron to form $C{u}^{+}$ ion with electronic configuration $\left[Ar\right]3d^{10}4s^0$
To remove second electron, completely filled stable 3d orbital configuration needs to be broken which requires huge amount of energy.
c) The spin only magnetic moment of $S{c}^{3+}$ is zero (Z=21).
The electronic configuration of $S{c}^{3+}=\left[Ar\right]3d^{0}4s^0$
Since number of unpaired electrons is zero, the spin only magnetic moment of $S{c}^{3+}$ is zero .