Question

What is the general molecular formula of the product obtained when lanthanoids are heated with sulphur?

Answer 1

General oxidation state of lanthanoid

• The general electron configuration of lanthanoid is $\left(n-2\right)f^{1-14}\left(n-1\right)d^{0-1}n{s}^2$.
• It is attained by removing the outermost two electrons of $s$ orbital and 1 electron from $f$orbital.
• It is due to the high energy difference in $4f$and $6s$, it is difficult to remove more electrons from $4f$ sub-shell.
• So, the most stable oxidation state of the elements of the lanthanoids series is $+3$.

Chemical reaction of lanthanoid with sulfur

• The reaction is as follows:-

$2\mathrm{Ln}+3\mathrm{S}\to {\mathrm{Ln}}_2{\mathrm{S}}_3$

• So, the molecular formula of the product obtained when lanthanoids are heated with sulfur is ${\mathrm{Ln}}_2{\mathrm{S}}_3$.