Consider the following ionization enthalpies of two elements ‘A’ and ‘B’.
Element - Ionization - enthalpy (kJ/mol)
1st - 2nd - 3rd
A 899 - 1757 - 14847
B 737 - 1450 - 7731
Which of the following statements is correct?
(a) Both ‘A’ and ‘B’ belong to group–1 where ‘B’ comes below ‘A’.
(b) Both ‘A’ and ‘B’ belong to group–1 where ‘A’ comes below ‘B’.
(c) Both ‘A’ and ‘B’ belong to group–2 where ‘B’ comes below ‘A’.
(d) Both ‘A’ and ‘B’ belong to group–2 where ‘A’ comes below ‘B’.
Correct answer:(c) Both ‘A’ and ‘B’ belong to group–2 where ‘B’ comes below ‘A’.
Explanation:
Generally, the ionization enthalpies or energy increases from left to right in a period and decreases from top to bottom in a group. Several factor such as atomic radius, nuclear charge, shielding effect are responsible for change of ionization enthalpies.
Here, Ist ionization enthalpy of A and B is greater than group I (Li = 520 kJmol–1 to Cs = 374 kJmol–1), which means element A and B belong to group –2 and all three given ionization enthalpy values are less for element B means B will come below A.