Question

(a). Chemistry of all the lanthanoids is quite similar.
(b). The actinide contraction differs from lanthanide contraction? Explain
(c). A serious accident occurred in a chemistry laboratory when a student tried to dissolve excess of `KMnO_4` in conc. `H_2SO_4`.

Answer 1

(a). The change in the size of the lanthanoids due to lanthanoid contraction is very small as we proceed from `La(Z=57)` to `Lu(Z=71)`. Hence, their chemical properties are similar. Moreover their valence shell configuration remains the same because the electron are added into the inner 4f-subshell. Hence, they show similar chemical properties.
(b). Lanthanide contraction refers to the gradual decrease in the size of the anthanoids and their trivalent ions. `(Z=58` to 71) whereas actinoid series refers to the gradual decrease in the size of the actinoids or their ions `(M^(3+)` or `M^(4+))(Z=90` to 103). They differ in the fact that in the actinoid series, the contraction is greater from element to element due to poor shielding by 5f electrons than by 4f electrons.
(c). This is due to the formation of high explosive oily substance `Mn_2O_7` which is responsible for the accident
`2KMnO_4+H_2SO_4toK_2SO_4+Mn_2O_7+H_2O`
`2Mn_2O_7overset(Explodes)to4MnO_2+3O_2`