Which of the following best describes the trend in ionization energy as you move from left to right across a period in the periodic table?

• A. Ionization energy increases.
• B. Ionization energy remains constant.
• C. Ionization energy first increases, then decreases.
• D. Ionization energy decreases.

Answer: (A)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from a gaseous atom or ion.
2. Recall that as you move from left to right across a period in the periodic table, the number of protons in the nucleus increases, which increases the nuclear charge.
3. Recognize that the increased nuclear charge pulls the electrons closer to the nucleus, making it harder to remove an electron.
4. Note that the shielding effect remains relatively constant across a period because electrons are added to the same principal energy level, so it does not significantly offset the increased nuclear charge.
5. Conclude that because the effective nuclear charge increases and shielding remains similar, the ionization energy generally increases from left to right across a period.