Which electron configuration represents a potassium atom in an excited state?

June 2018 NY Regents Chemistry Exam

35 Which electron configuration represents a potassium atom in an excited state?
(1) 2-7-6

(2) 2-8-5

(3) 2-8-8-1

(4) 2-8-7-2

Solution: When an electron is excited, it moves from a lower energy level to higher. We can find potassium's(K) electron configuration on the Periodic Table. It is 2-8-8-1.This means 2 electrons in the first energy level, 8 in the second, 8 in the third and 1 in the fourth. If we look at choice 4, we see 2-8-7-2. One of the electrons in the third energy level moved up to the fourth energy level.

Answer: 4

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