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?

 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.

Need help with your chemistry class? Our Online Chemistry Tutor is ready to help you!