Question

Question 3.19 The first ionization enthalpy values (in kJmol–1) of group 13 elements are :




B Al Ga In TI


801 577 579 558 589


How would you explain this deviation from the general trend?

Class XI Classification of Elements and Periodicity in Properties Page 93

Answer 1

$B\: \: \: \: \: \: Al\: \: \: \: \: \: \: \: \: \: Ga \: \: \: \: \: \: \: \: \:In \: \: \: \: \: \: \: \: \: \:Ti\\801 \: \: \: \: \: \:577 \: \: \: \: \: \:579 \: \: \: \: \: \:558 \: \: \: \: \: \: \: \:589$
In general we know, when we move down the group , Ionisation enthalpy decreases due to increases atomic size.
But Ionisation enthalpy of Ga is higher than Al. it is due to 'imperfect shielding of the valance electrons by 3d - electrons . as a result of this effective nuclear charge of Ga is slightly higher than Al . that's why Ga has higher Ionisation enthalpy than Al.

on moving from In to Ti , Ionisation enthalpy of Ti is higher than In . it is due to the fact of inert pair effect { d - and f - electrons shield the valance shell electrons from the nucleus less effectively than s- and p- electrons }

Answer 2

Answer:

In general we know, when we move down the group , Ionisation enthalpy decreases due to increases atomic size.

But Ionisation enthalpy of Ga is higher than Al. it is due to 'imperfect shielding of the valance electrons by 3d - electrons . as a result of this effective nuclear charge of Ga is slightly higher than Al . that's why Ga has higher Ionisation enthalpy than Al.

on moving from In to Ti , Ionisation enthalpy of Ti is higher than In . it is due to the fact of inert pair effect { d - and f - electrons shield the valance shell electrons from the nucleus less effectively than s- and p- electrons }

E