Which of the following best explains why electronegativity increases as we move up a group in the periodic table?

• A. Atoms have fewer electron shells, so the valence electrons are closer to the nucleus and more strongly attracted.
• B. Atoms have more protons, which increases the nuclear charge and decreases electronegativity.
• C. Atoms have larger atomic radii, making it easier to attract electrons.
• D. Atoms have more electron shielding, which increases the ability to attract electrons.

Answer: (A)

Verified step by step guidance

1. Understand that electronegativity is the tendency of an atom to attract electrons towards itself in a chemical bond.
2. Recognize that as you move up a group in the periodic table, the number of electron shells decreases, meaning valence electrons are closer to the nucleus.
3. Recall that the closer the valence electrons are to the nucleus, the stronger the electrostatic attraction between the nucleus and the electrons, which increases electronegativity.
4. Note that moving up a group also means less electron shielding because there are fewer inner electron shells to block the nuclear charge.
5. Conclude that fewer electron shells and less shielding result in a stronger effective nuclear charge felt by valence electrons, thus increasing electronegativity as you move up a group.