Atoms form bonds to get a full outer shell of valence electrons. Atoms or groups of atoms that have an electric charge due to losing or gaining electrons are called ions. In an ionic bond, metals give away their electrons becoming positive ions, and nonmetals take them becoming negative ions. Ionic bonds have strong bonds, are good conductors of electricity, have high densities, have high melting and boiling points, and form crystal structures which are compounds of ions. Covalent bonds form molecules, which are compounds, of nonmetals bonded with other nonmetals where two atoms share electrons between themselves. Covalent bonds have weak bonds, are bad conductors of electricity, have low densities, and have low melting and boiling points.
