Ion

• an atom or group of atoms with a net electric charge, due to gaining or losing electrons
• $\text{ion charge}=\text{\# of protons}-\text{\# of electrons}$
• notated as element’s symbol with superscript that shows the charge
  • when the charge is $1+$ or $1-$, the $1$ is usually omitted
  • ex. a magnesium ion with a $2+$ charge is written as $\mathrm{Mg}{}^{2+}$
  • ex. a sodium ion with a $1+$ charge is written as $\mathrm{Na}{}^{+}$, not $\mathrm{Na}{}^{1+}$
• cation - a positively charged ion (cat-ion)
  • when an atom loses electron(s)
  • name is the same as the neutral element
    • ex. $\mathrm{H}{}^{+}$ is a hydrogen ion
• anion - a negatively charged ion (an-ion)
  • when an atom gains electron(s)
  • name ends in -ide
    • ex. $\mathrm{Cl}{}^{-}$ is a chloride ion, $\mathrm{N}{}^{3-}$ is a nitride ion

Polyatomic ions

• groups of atoms that stay bonded together while carrying a net electric charge
• made of multiple atoms, but act as a single unit in chemical reactions
• some common polyatomic ions:

  Name ⇅	Chemical formula ⇅
  hydroxide	$\mathrm{OH}{}^{-}$
  ammonium	$\mathrm{NH}{}_4{}^{+}$
  phosphate	$\mathrm{PO}{}_4{}^{3-}$