The first-ionization energies (IE₁) for the elements in period 2 are shown in the table
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
The first-ionization energies (IE₁) for the elements in period 2 are shown in the table.
Element
Li
Be
B
C
N
O
F
Ne
IE₁ (kJ·mol⁻¹)
520
900
801
1086
1402
1314
1681
2080
Two notable decreases in IE₁ occur despite increasing atomic number.
(a) Identify the two pairs of adjacent elements between which IE₁ decreases rather than increases.
(b) For the earlier anomaly you identified, explain the decrease in IE₁ in terms of subshell occupancy and the resulting shielding of the electron being removed.
(c) For the later anomaly you identified, explain the decrease in IE₁ by discussing electron–electron repulsion and its effect on the attraction between the nucleus and the electron being removed.
(d) Relate your explanations in parts (b) and (c) to the general concept of effective nuclear attraction, highlighting the common underlying principle.