Question

(a) Using Valence Bond theory prove that ${\left[Ni{\left(CN\right)}_4\right]}^{2-}$ is diamagnetic, whereas ${\left[Ni{\left({NH}_3\right)}_4\right]}^{2+}$ is paramagnetic:
(b) Explain Radiocarbon dating?

Answer 1

(a) ${\left[Ni{\left(CN\right)}_4\right]}^{2-}$ is diamagnetic, whereas ${\left[Ni{\left({NH}_3\right)}_4\right]}^{2+}$ is paramagnetic.
In ${\left[Ni{\left(CN\right)}_4\right]}^{2-}$, the central $N{i}^{2+}$ ion has outer electronic confiiguration $3d^8$ electronic configuration and is $ds{p}^2$ hybridised. Since, all electrons are paired, it is diamagnetic.
In ${\left[Ni{\left({NH}_3\right)}_4\right]}^{2+}$ the central $N{i}^{2+}$ ion has outer electronic confiiguration $3d^8$ electronic configuration and is $s{p}^3$ hybridised.
It has two unpaired electrons and, is paramagnetic.

(b) Radiocarbon dating is used to find the age of fossils and old wood with the help of C-14.
$t=\frac{2.303}{\lambda }lo{g}_{10}\frac{N_0}{N}$
$t=$ age of fossils and old wood
$\lambda =$ decay constant
$N_0=$ original activity or amount or ratio of C-14/C-12 in fresh sample
$N=$ activity or amount or ratio of C-14/C-12 in old sample