Question

Which element from the following has the highest ionisation energy ?

(a) P, Na, Cl (b) F, O, Ne (c) Ne, He, Ar

Explain your choice.

Answer 1

(a) P, Na, Cl (b) F, O, Ne


The following are the ionization energies for the elements in the second period:

Lithium - 520
Beryllium - 900
Boron - 801
Carbon - 1087
Nitrogen - 1402
Oxygen - 1314
Fluorine - 1681
Neon - 2081
Hence, arranging them according to increasing ionization energy, we get:

Li < B < Be < C < N < O < F < Ne.

The following are the ionization energies for elements in the third period:

Sodium - 496
Magnesium - 738
Aluminum 578
Silicon - 787
Phosphorus - 1012
Sulfur - 1000
Chlorine - 1251
Argon - 1521
Hence, the order is as follows:

Na < Al < Mg < Si < S < P < Cl < Ar