Which of the following gives a possible quantum number assignment for the last electron added to the sodium atom when developing the electron configuration using the aufbau principle?
n l ml ms
A)4 1 -1 0
B)3 2 +1 -1⁄2
C)3 1 -1 1⁄2
D)3 0 0 1⁄2
E)2 1 -1 -1⁄2
Solution: The electron configuration of sodium is [Ne] 3s1
That means that the last electron is in the 3s orbital. The first number represents the n quantum number. Therefore, n must be equal to 3, eliminating choices A and E. The letter refers to the l quantum number.
When l=0, the letter is s. When l=1, the letter is p. When l=2, the letter is d. In this case, the letter is "s" which means l must be equal to 0. Choice D must be the correct answer choice.
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