Which statement correctly describes the trend in ionization energy within a group of the periodic table?

• A. Ionization energy increases as you move down a group.
• B. Ionization energy remains constant as you move down a group.
• C. Ionization energy first increases and then decreases as you move down a group.
• D. Ionization energy decreases as you move down a group.

Answer: (D)

Verified step by step guidance

1. Recall that ionization energy is the energy required to remove an electron from a gaseous atom or ion.
2. Understand that within a group (column) of the periodic table, atoms have the same number of valence electrons but increasing numbers of electron shells as you move down.
3. Recognize that as you move down a group, the outermost electrons are farther from the nucleus due to the addition of electron shells, which increases the atomic radius.
4. Consider that the increased distance and the shielding effect from inner electrons reduce the effective nuclear charge felt by the outermost electrons, making them easier to remove.
5. Conclude that because of these factors, ionization energy decreases as you move down a group in the periodic table.