Which of the following best helps explain why the electronegativity of sodium (Na) is less than that of chlorine (Cl)?

• A. Chlorine is a metal, while sodium is a nonmetal, and nonmetals generally have lower electronegativity.
• B. Sodium has a lower effective nuclear charge than chlorine, resulting in a weaker attraction for bonding electrons.
• C. Sodium is located further to the right on the periodic table than chlorine, so its electronegativity is lower.
• D. Sodium has more valence electrons than chlorine, making it less likely to attract additional electrons.

Answer: (B)

Verified step by step guidance

1. Understand the concept of electronegativity: it is the tendency of an atom to attract bonding electrons toward itself in a chemical bond.
2. Recall that effective nuclear charge (Z_eff) is the net positive charge experienced by valence electrons, calculated as the actual nuclear charge (number of protons) minus the shielding effect of inner electrons.
3. Compare sodium (Na) and chlorine (Cl): Sodium has 11 protons and fewer valence electrons, while chlorine has 17 protons and more valence electrons, leading to a higher effective nuclear charge in chlorine.
4. Recognize that a higher effective nuclear charge means a stronger attraction for bonding electrons, so chlorine attracts electrons more strongly than sodium.
5. Conclude that the best explanation for the difference in electronegativity is that sodium has a lower effective nuclear charge than chlorine, resulting in a weaker attraction for bonding electrons.