Which electron configuration represents the electrons of an atom in an excited state?

January 2018 NY Regents Chemistry Exam

32 Which electron configuration represents the electrons of an atom in an excited state?

(1) 2–2

(2) 2–2–1 (3) 2–8

(4) 2–8–1

Solution: When an electron is excited, it moves from a lower energy level to higher. The first energy level has a maximum of 2 electrons. The second energy level has a maximum of 8 electrons. The third energy level has a maximum of 8 electrons. If we look at choice 2, we see 2-2-1. This means 2 electrons in the first enegy level, 2 electrons in the second energy level and 1 in the third energy level. We know that the second level has a maximum of 8 electrons. Yet, it has only 2 electrons and another electron in the third level. This means that one of the electrons in the second level went up to the third level (got excited).

Answer: 2

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