With metallic bonding,the valence electrons form a"sea of electrons"that is uniformly dispersed around the metal ion cores and acts as a form of glue for them.Both van der Waals and hydrogen bonds are termed secondary,being weak in comparison to the primary ones.They result from attractive forces between electric dipoles.of which there are two types-induced and permanent.For the hydrogen bond,highly polar molecules form when hydrogen covalently bonds to a nonmetallic element such as fluorine.