List all the possible sets of quantum numbers for the n = 2 shell, and determine the number of electrons that can be in the shell and each of its subshells.

Strategy

Given n = 2 for the shell, the rules for quantum numbers limit l to be 0 or 1. The shell therefore has two subshells, labeled 2s and 2p. Since the lowest l subshell fills first, we start with the 2s subshell possibilities and then proceed with the 2p subshell.