Ionic bonds form stable crystals, but are weaker bonds in water.
Ionic compounds are called salts (e.g. NaCl or table salt).
NOTE: Difference in electronegativity determines if electrons are shared equally, shared unequally, gained or lost. Nonpolar covalent bonds and ionic bonds are two extremes of a continuum from interacting atoms with similar electronegativities to interacting atoms with very different electronegativities.