5.2 - Ionic Bond

Formation of Ions

• An ionic bond involves electron transfer between a metal atom and a non-metal atom.
• A metal atom donates valence electron(s) and becomes a positively charged ion, or cation.
• A non-metal atom accepts electron(s) and becomes a negatively charged ion, or anion.
• Electron transfer gives both ions a stable duplet or octet electron arrangement.

For sodium and fluorine:

$\mathrm{Na}\to \mathrm{N}{\mathrm{a}}^{+}+{\mathrm{e}}^{-}$

$\mathrm{F}+{\mathrm{e}}^{-}\to {\mathrm{F}}^{-}$

• A sodium atom, with electron arrangement 2.8.1, donates one electron to form $\mathrm{N}{\mathrm{a}}^{+}$ with arrangement 2.8.
• A fluorine atom, with arrangement 2.7, accepts one electron to form ${\mathrm{F}}^{-}$ with arrangement 2.8.
• Donating one electron is easier for sodium than accepting seven; accepting one is easier for fluorine than donating seven.
• $\mathrm{N}{\mathrm{a}}^{+}$ has 11 protons and 10 electrons, giving a net charge of +1. ${\mathrm{F}}^{-}$ has 9 protons and 10 electrons, giving a net charge of −1.

Formation of an Ionic Bond

• Oppositely charged ions attract one another through a strong electrostatic attraction force.

• This electrostatic attraction is the ionic bond.

• In sodium fluoride, $\mathrm{N}{\mathrm{a}}^{+}$ and ${\mathrm{F}}^{-}$ attract to form the ionic compound $\mathrm{NaF}$.

• Ionic compounds are electrically neutral overall: the total positive charge equals the total negative charge.

• Other ionic-compound examples include magnesium oxide, $\mathrm{MgO}$; sodium chloride, $\mathrm{NaCl}$; and sodium oxide, $\mathrm{N}{\mathrm{a}}_2\mathrm{O}$.
• Sodium fluoride is added to toothpaste to strengthen teeth.