# Which period is Ca (20) in?

Aug 8, 2018

Surely there must be a Periodic Table in front of you if you are doing your chemistry homework?

#### Explanation:

The one in front of me now tells me that calcium, $Z = 20$, belongs in the FOURTH Period, the fourth row on the Periodic Table....and thus its valence electrons are $4 s$. The electronic configuration of the metal is...

$1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2}$

...the electronic configuration of the common ion, $C {a}^{2 +}$ is thus...

${\left\{1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6}\right\}}^{2 +}$