# One chlorine (Cl) atom combines with one sodium (Na) atom. How many potassium (K) atoms combines with a chlorine atom?

$\text{Sodium chloride, potassium chloride, rubidium chloride,}$ $\text{caesium chloride,}$ all have a formula of $M C l$, where $M$ is the alkali metal. All the alkali metals have similar electronic configurations; thus they have the same type of interaction with the chloride ion, i.e. $C {l}^{-}$ (and the same interaction with all of the halogens).