JEE Main Chemistry Class 11 Classification of Elements and Periodicity in Properties 1 Questions

Given data,

	IE1	IE2
X	495	4563 kJ/mol
Y	71	1450 kJ/mol

X is Na(3s1) as it has very high second ionisation energy due to removal of electron from highly stable noble gas configuration.

Na IE1 ⟶

1s22s22p63s1

‌‌‌‌

Na++e−;‌‌IE1

1s22s22p6‌or[Ne]

=495kJ/mol

Na+

1s22s22p6

IE2

⟶

Na2++e−;

1s22s22p5

IE2=4563kJ/mol
(Stable noble gas configuration).
In case of Mg, noble gas configuration is achieved after removal of second electron. So, IE2 is comparatively less.

Mg

[Ne]3s2

⟶

Mg+

[Ne]3s1

+e−;IE1=731kJ/mol

Mg+

[Ne]3s1

⟶

Mg2+

[Ne]

+e−;IE2=1450kJ/mol