Definition: One partner gets the electron and keeps it ALL THE TIME Definition: Both partners share the electron equally
Happens between: Metals with nonmetals
Happens between:  nonmetals with each other
Examples: NaCl, MgO
Examples: H2, CO2
In naming these compounds you may see Roman Numerals, as in Iron III Chloride
In naming these compounds you may see prefixes that tell you 'how many', such as mono, tri, and hexa

Ionic Compounds

  1. Crystalline solids (made of ions)
  2. High melting and boiling points
  3. Conduct electricity when melted
  4. Many soluble in water but not in nonpolar liquid

Covalent Compounds

  1. Gases, liquids, or solids (made of molecules)
  2. Low melting and boiling points
  3. Poor electrical conductors in all phases
  4. Many soluble in nonpolar liquids but not in water

The Li atom loses it electron to the F atom

The O atom shares electrons with H atoms
Here is part of a salt crystal.  The atoms are held together by electrical attractions between positive and negative ions.
Here is an ionic crystal called Fluorite.  It is very hard to melt or dissolve.
Here is part of a diamond.  Each dot is a carbon atom.  Each carbon atom shares electrons with its four neighbors.

Here is a chunk of dry ice (CO2).  Unlike the strong covalent  bonds in diamond, dry ice only has weak internolecular forces holding it together.  Dry ice is hard to keep together!