Types of Bonds

Type	Relative strength	Principle	Example
Ionic	Strongest	Electrostatic attraction between positive and negative ions	NaCl crystal
Covalent	Strong	Sharing of electrons between atoms: the nuclei of both atoms are pulled toward the shared electrons	C-C bond
Dipole-dipole	Weak to moderate	Electrostatic attraction between partially positive and partially negative parts of neutral molecules	CH3Cl; hydrogen bonding in ethanol
van der Waals (or London forces or dispersion forces)	Weakest	Transient dipoles: random accumulation of electrons on one side of a molecule creates a dipole moment, which may in turn induce dipoles in other molecules	Methane
Metallic	Moderate to strong	Positive nuclei in a "sea" of mobile electrons	Aluminum