January 2020 NY Regents Chemistry Exam
9 Which part of a calcium atom in the ground state is represented by the dots in its Lewis electron- dot diagram? (1) the electrons in the first shell
(2) the electrons in the fourth shell
(3) the protons in the nucleus (4) the neutrons in the nucleus
Solution: Dots in the Lewis electron- dot diagram represent valence electrons (electrons in the outermost shell). Looking at the Periodic Table, we see that the electron configuration for calcium is 2-8-8-2. This means it has 2 electrons in the first shell, 8 in the second shell, 8 in the third shell and 2 in the fourth shell. It must have 2 valence electrons in the fourth shell.
Answer: 2
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