Ionic or covalent? Modelling chemical bonds

Atoms bond to get a full outer shell of electrons. When a metal meets a non-metal, the metal atom gives its outer electrons to the non-metal atom. The metal becomes a positive ion and the non-metal a negative ion, and the opposite charges attract: an ionic bond. Ionic compounds have high melting points and conduct electricity when molten or dissolved. When non-metal atoms bond, neither gives up electrons; they share pairs of electrons instead: a covalent bond. Covalent substances made of small molecules usually have low melting points and do not conduct.