Which statement is true about electronegativity across a period?

• A. Increases across a period
• B. Decreases across a period
• C. Increases down a group
• D. Decreases down a group

Answer: (A)

Electronegativity is the tendency of an atom to attract electrons in a chemical bond. Across a period, from left to right, the nucleus gains more protons while the electrons are added to the same valence shell. This increases the effective nuclear charge felt by bonding electrons, pulling them more strongly toward the nucleus. At the same time, the atomic radius decreases, bringing the bonding electrons closer to the nucleus. The net effect is a stronger attraction for shared electrons as you move to the right, so electronegativity increases across a period. Down a group, electrons are added to higher energy levels, shielding increases, and the atomic radius grows, weakening the nucleus’s pull on bonding electrons; thus electronegativity decreases down a group.