# Given the following, how many protons are in an atom of chlorine? What is the atomic number of sodium?

## An atom of chlorine (Cl) has 6 more protons than an atom of sodium (Na). The atomic number of chlorine is 5 less than twice the atomic number of sodium. The atomic number of an element is equal to the number of protons per atom.

May 14, 2017

For $C l$, $Z = 17$.
$Z = \text{the atomic number}$, the number of massive, positively charged nuclear particles. $Z$ defines the identity of the element. For $C l$, $Z = 17$.
We are given that ${Z}_{\text{Na"+6=Z_"Cl}}$, and thus ${Z}_{\text{Na}} = 11$.
And $2 \times {Z}_{\text{Na"-5=22-5=17=Z_"Cl}}$ as required.