Why does ionization energy generally increase from left to right across a period on the periodic table?

• A. Because atomic radius increases, making electrons easier to remove.
• B. Because the nuclear charge increases, causing a stronger attraction between the nucleus and valence electrons.
• C. Because the number of electron shells increases, making it harder to remove an electron.
• D. Because the number of valence electrons decreases, increasing the energy required to remove one.

Answer: (B)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from an atom in its gaseous state.
2. Recognize that as you move from left to right across a period, the number of protons in the nucleus (nuclear charge) increases, which means the positive charge attracting the electrons becomes stronger.
3. Note that although electrons are being added as you move across a period, they are added to the same principal energy level (same shell), so the shielding effect does not increase significantly.
4. Because the increased nuclear charge is not effectively shielded, the attraction between the nucleus and the valence electrons becomes stronger, making it more difficult to remove an electron.
5. Therefore, ionization energy generally increases from left to right across a period due to the increasing nuclear charge and stronger attraction to valence electrons.