# Both of calcium's electrons are in its innermost shell. Why is this?

$1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2}$
The first two ($1 {s}^{2}$) are in the innermost energy level/shell and the last two ($4 {s}^{2}$) are in the outermost energy level/shell. These last two are also the most likely to be removed to make a calcium ion.