Which element in the third period would you expect to have the larger atomic radius, sodium (Na) or Sulfur (S)?

Question

Sodium because it has a higher effective nuclear charge attracting electrons in fewer energy levels.
Sodium because it has fewer protons attracting electrons in the same energy levels.
Sulfur because it has more protons attracting electrons in more energy levels.
Sulfur because it has a higher effective nuclear charge attracting electrons in the same energy levels.

Answer 1

The correct reasoning is:

Sodium (Na) because it has fewer protons attracting electrons in the same energy levels.

This is because atomic radius generally decreases across a period due to the increasing effective nuclear charge from the added protons, which pulls the electrons closer to the nucleus. Sodium, which is located to the left of sulfur on the periodic table, has fewer protons (11) compared to sulfur (16), resulting in a larger atomic radius for sodium due to less effective nuclear pull on the outer electrons.