Ionization energies of elements _________ down a group and generally __________ across a period.

• A. increase; increase
• B. decrease; increase
• C. decrease; decrease
• D. increase; decrease

Answer: (B)

Verified step by step guidance

1. Understand the concept of ionization energy: it is the energy required to remove an electron from a gaseous atom or ion.
2. Recall the trend down a group in the periodic table: as you move down a group, atomic size increases due to additional electron shells, which causes the outer electrons to be farther from the nucleus and more shielded by inner electrons.
3. Because of this increased distance and shielding, the attraction between the nucleus and the outermost electron decreases, so ionization energy decreases down a group.
4. Recall the trend across a period: as you move from left to right across a period, the nuclear charge increases (more protons) while the shielding effect remains relatively constant, pulling electrons closer to the nucleus.
5. This stronger attraction makes it harder to remove an electron, so ionization energy generally increases across a period.