Question

The first ionsation enthalpies of the alkaline earth metals are higher than that of alkali metals but second ionisation enthalpies are smaller, why?

• A. In alkali metals, second ionisation enthalpy involves removal of electron from noble gas electronic configuration while in alkaline earth metals, second electron is removed from $ns^{1}$ configuration.
• B. Alkaline earth metals have very high melting point as compared to alkali metals.
• C. Electrons in s – orbital are more closely packed in alkaline earth metals than alkali metals.
• D. Due to smaller size alkaline earth metals do not form divalent ions very easily.

Answer 1

Answer: (A)

In alkali metals, second ionisation enthalpy involves removal of electron from noble gas electronic configuration while in alkaline earth metals, second

electron is removed from $ns^{1}$ configuration.

Answer 2

:Alkaline earth metals –

$\underset{ns^{2}}{M} - le^{-}\overset{\quad IE_{1}\quad}{\rightarrow}\underset{ns^{1}}{M^{+}}\underset{- le^{-}}{\overset{\quad IE_{2}\quad}{\rightarrow}}\underset{(Noblegasconfiguration)}{M^{2 +}}$

Alkali metal

}{IE_{2} > > IE_{1}}$$