Ionic Compounds

Ionic Compounds Compounds that contain ions are called Ionic Compounds. e.g. sodium chloride has the formula NaCl – this means the ratio of sodium ions (Na+), to chloride ions (Cl-) is 1:1 A small crystal of NaCl contains billions of sodium ions and chloride ions in a lattice structure.

Ionic Compounds Every ionic compound contains cations and anions held together by the attraction of their opposite charges. Ionic compounds form between metals and non-metals. In solution, they conduct electricity.

NaF – single charge ions Sodium atom Fluorine Atom F - + Na Fluoride Ion Sodium ion

MgS – double charge ion Mg S Mg S Magnesium atom Sulfur Atom 2+ 2- Magnesium Ion Sulfide Ion

Writing Ionic Formulae Ionic compounds contain cations and anions. The number of positive charges must be balanced by an equal number of negative charges.

Examples Mg2+ O2- A magnesium ion has a charge of 2+ and an oxide ion has a charge of 2-. They are equal so the formula for magnesium oxide is MgO, with 1 Magnesium and 1 Oxide.

Example Cl- Ca2+ Calcium has a charge of 2+ but chloride only has 1-. The charges are not equal. Charges need to be balanced by adding another chloride ion. CaCl2 Cl- Ca2+ Cl-