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

Question

The first ionisation 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

Tardigrade Admin · Accepted Answer

Alkaline earth metals - undersetns2M-1e- xrightarrowIE1 undersetns1M+ xrightarrow[-1e-]IE2 underset text(Noble gas configuration)M2+ Alkali metals - undersetns1M-1e- xrightarrowIE1 underset text(Noble gas configuration)M+ xrightarrowIE2 M2+ ; IE2 >>IE1

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

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 $n s^{- 1}$ configuration

Alkaline earth metals have very high melting point as compared to alkali metals

Electrons in $s$ -orbital are more closely packed in alkaline earth metals than alkali metals

Due to smaller size alkaline earth metals do not form divalent ions very easily

Alkaline earth metals -
$n s^{2} M - 1 e^{-} I E_{1} n s^{1} M^{+} I E_{2} - 1 e^{-}$ $(Noble gas configuration) M^{2 +}$
Alkali metals -
$n s^{1} M - 1 e^{-} I E_{1} (Noble gas configuration) M^{+} I E_{2} M^{2 +}$ ;
$I E_{2} >> I E_{1}$

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

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

Alkaline earth metals have very high melting point as compared to alkali metals

Electrons in s-orbital are more closely packed in alkaline earth metals than alkali metals

Due to smaller size alkaline earth metals do not form divalent ions very easily

Alkaline earth metals - ns2M​−1e−IE1​​ns1M+​IE2​−1e−​ (Noble gas configuration)M2+​ Alkali metals - ns1M​−1e−IE1​​(Noble gas configuration)M+​IE2​​M2+ ; IE2​>>IE1​

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 $n s^{- 1}$ configuration

Electrons in $s$ -orbital are more closely packed in alkaline earth metals than alkali metals

Alkaline earth metals -
$n s^{2} M - 1 e^{-} I E_{1} n s^{1} M^{+} I E_{2} - 1 e^{-}$ $(Noble gas configuration) M^{2 +}$
Alkali metals -
$n s^{1} M - 1 e^{-} I E_{1} (Noble gas configuration) M^{+} I E_{2} M^{2 +}$ ;
$I E_{2} >> I E_{1}$