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Question 10 • Chemistry

The electron configuration for magnesium is shown. 1 s squared 2 s squared 2 p to the 6th power 3 s squared Which diagram shows the correct distribution of electrons in the electron shells of a magnesium atom?

Answer
A
Image with description 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.
B
Image with description 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.
C
Image with description 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.
D
Image with description 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.

Explanation

The configuration 1s² 2s² 2p⁶ 3s² contains 12 electrons: 2 in the first shell, 8 in the second, and 2 in the third. Magnesium has 12 protons, and the diagrams show its nucleus as 12 P 12 N. Choice C shows the shell distribution 2, 8, 2; choice D has only one electron in the outer shell.

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