What happens to the atomic size when the principal quantum number n increases?

What happens to the atomic size when the principal quantum number n increases?

• A. Size decreases
• B. Size stays the same
• C. Size increases
• D. Size depends on the element

Answer: (C)

The principal quantum number n sets the shell that the outer electrons occupy. When n increases, electrons reside in shells farther from the nucleus, so the average distance from the nucleus grows and the atomic radius becomes larger. In a simple hydrogen-like picture, the radius scales roughly with n^2, showing this direct link between higher n and a bigger size. In real atoms, inner electrons shield outer ones and alter the effective nuclear charge, but the fundamental idea holds: increasing n pushes the outer electrons outward, increasing atomic size.

The principal quantum number n sets the shell that the outer electrons occupy. When n increases, electrons reside in shells farther from the nucleus, so the average distance from the nucleus grows and the atomic radius becomes larger. In a simple hydrogen-like picture, the radius scales roughly with n^2, showing this direct link between higher n and a bigger size. In real atoms, inner electrons shield outer ones and alter the effective nuclear charge, but the fundamental idea holds: increasing n pushes the outer electrons outward, increasing atomic size.