As you move from left to right across a period (row) on the periodic table, what happens to the ionization energy of the elements?

• A. Ionization energy increases.
• B. Ionization energy remains constant.
• C. Ionization energy decreases.
• D. Ionization energy first increases, then 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, 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 them harder to remove.
4. Note that the shielding effect remains relatively constant across a period because electrons are added to the same principal energy level.
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.