Which of the following best explains why the period (row) an element is in affects its electronegativity?

• A. Elements in the same period have identical electronegativity values because they have the same number of electron shells.
• B. Electronegativity decreases across a period because atomic radius increases, making it harder for the nucleus to attract electrons.
• C. As you move across a period, the number of protons increases, causing a stronger attraction between the nucleus and valence electrons, which increases electronegativity.
• D. Electronegativity is unaffected by the period because only the group (column) matters.

Answer: (C)

Verified step by step guidance

1. Understand that electronegativity is the tendency of an atom to attract electrons in a chemical bond.
2. Recognize that elements in the same period (row) have the same number of electron shells, so the shielding effect remains relatively constant across a period.
3. Note that as you move from left to right across a period, the number of protons in the nucleus increases, which increases the positive charge attracting the electrons.
4. Because the number of electron shells stays the same but the nuclear charge increases, the effective nuclear attraction on valence electrons becomes stronger, leading to higher electronegativity.
5. Therefore, the period affects electronegativity primarily due to the increasing nuclear charge across the period, not because of changes in atomic radius or electron shells.