Question

The electron configuration for magnesium is shown below.

1s22s22p63s2

Which diagram shows the correct distribution of electrons in the electron shells of a magnesium atom?

A gray circle labeled 3 P 4 N is surrounded by two concentric circles. The inner circle has gray dots at the north and south positions, and the outer circle has a dot at the north position.

A gray circle labeled 4 P 5 N is surrounded by two concentric circles. Each of the concentric circles has gray dots at the north and south positions.

A gray circle labeled 12 P 12 N is surrounded by three concentric circles. The innermost circle has gray dots at the north and south positions; the middle circle has eight gray dots equally spaced around the circle, with dots aligned with those in the inner circle; the outer circle has gray dots at the north and south positions.

A gray circle labeled 12 P 12 N is surrounded by three concentric circles. The innermost circle has gray dots at the north and south positions; the middle circle has eight gray dots equally spaced around the circle, with dots aligned with those in the inner circle; the outer circle has a gray dot at the north position.

Answer 1

The third diagram — the one labeled "12 P 12 N" with three shells showing 2 electrons in the innermost shell, 8 in the second shell, and 2 in the outermost shell. This matches Mg (Z = 12) and the electron distribution 2, 8, 2 from 1s2 2s2 2p6 3s2.