Question

(i) With reference to structural variability and chemical reactivity, write the difference between lanthanoids and actinoids.
(ii) Name a member of the lanthanoid series which is well known to exhibit $+4$ oxidation state.
(iii) Complete the following equation:
$Mn{O}_4^{-}+8H^{+}+5e^{-}\to$
(iv) Out of ${Mn}^{3+}$ and ${Cr}^{3+}$, which is more paramagnetic and why?

(atomic number : $Mn=25,Cr=24$)

Answer 1

(i) The difference between lanthanoids and actinoids with respect to their structural variability and chemical reactivity are as follows:

a) Actinoids are radioactive, while lanthanoids are not radioactive.

b) The ionisation enthalpies of the early actinoids are lower than those of the early lanthanoids. Actinoids show the oxidation state from +3 (most common) to +7, while lanthanoids show the oxidation state from +3 up to +7.

c) Actinoids are more reactive and have more complex magnetic properties than lanthanoids.

(ii) Cerium is a lanthanoids element that is known to exhibit the oxidation state of +4.

(iii) The complete equation is as follows :

$Mn{O}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O$

(iv) $M{n}^{2+}$ is more paramagnetic because it has more number of unpaired electrons than $C{r}^{3+}$ $(5u.e^{-}>3u.e^{-})$.