Concept preview

What you will be able to do

1. 01Predict monatomic ion charges from the periodic table
2. 02Name monatomic ions and recall common polyatomic ions
3. 03Construct an ionic formula using the criss-cross method

Going across the periodic table, each column forms ions of a predictable charge: column 1 gives $+1$ ($\mathrm{Na^+}$, $\mathrm{K^+}$), column 2 gives $+2$ ($\mathrm{Mg^{2+}}$, $\mathrm{Ca^{2+}}$), column 13 gives $+3$ ($\mathrm{Al^{3+}}$), then across the right side column 15 gives $-3$ ($\mathrm{N^{3-}}$), column 16 gives $-2$ ($\mathrm{O^{2-}}$, $\mathrm{S^{2-}}$), column 17 gives $-1$ ($\mathrm{F^-}$, $\mathrm{Cl^-}$) and column 18 (noble gases) gives $0$. Metals form positive ions (cations) and nonmetals form negative ions (anions).