Ionic Compounds CHEMISTRY 11 MS. MCGRATH

Ionic Compounds Ionic compounds do not form molecules. Why not? Think about NaCl…there is are the exact number of sodium ions and chloride ions

Ionic Compounds Crystal Lattice Due to their opposite charge, an attractive force exists between every sodium ion and every chloride ion which surrounds it In ionic compounds, the ions pack together in a way that that allows the positive and negative charges to be positioned as close together as possible This 3d arrangement of alternating positive and negative charges is called a crystal lattice

Ionic Compounds Crystal Lattice Because of this structure, there are no distinct pairs of sodium and chloride ions that we can identify as a “molecule”

Ionic Compounds Compounds such as calcium fluoride, CaF 2, have a two to one ratio of ions As you can see in the diagram, the structure of these crystalline solids is more complex than that of NaCl The ions still pack together in a way that allows the positive and negative ions to be as close together as possible

Ionic Compounds - Conclusion The unit cells do not function as independent units (ie. there is no specific group of ions that can be called a molecule Ionic bounds are attractive forces that among many positive and negative ions The chemical formulas for ionic compounds are called empirical formulas. These formulas represent the whole number ratio between the positive and negative ions in the smallest neutral unit of an ionic crystal lattice – the formula unit