Question

Why are the trends and exceptions to the trends in ionization energy observed? Check all that apply.

Ionization energy tends to increase down a group because the electrons get farther away from the nucleus.

Ionization energy tends to increase across a period because the nuclear charge increases.

Ionization energy tends to increase across a period because electrons are added to the same main energy level.

The ionization energies of the elements in Group 16 tend to be slightly smaller than the elements in Group 15 because the fourth electron is added to an unfilled p orbital.

The ionization energies of elements in Group 13 tend to be lower than the elements in Group 2 because the full s orbital shields the electron in the p orbital from the nucleus.

Answer 1

Check: 2, 3, 5.

Brief reasons:
- 1 (false): IE decreases down a group (not increases) because valence electrons are farther from the nucleus and more shielded.
- 2 (true): Across a period nuclear charge (effective Z) increases, pulling electrons in more tightly and raising IE.
- 3 (true): Across a period electrons enter the same principal energy level, so shielding doesn't increase much and IE rises.
- 4 (false): Group 16 IEs are slightly lower than Group 15 because the extra electron must pair up in a p orbital (electron–electron repulsion), not because it is added into an “unfilled” p orbital.
- 5 (true): Group 13 valence electrons are in a p orbital shielded by a filled s orbital, so their first IEs are lower than the preceding Group 2 s electrons.