Chemical bonds are the forces that hold atoms together, forming molecules. Chemical bonds may be divided into two groups: 1) covalent (strong) bonds in which atoms share electrons, and; 2) a variety of weak bonds, including electrostatic attractions (ionic bonds, hydrogen bonds), hydrophobic interactions, and Van der Waals forces.
The strength of a chemical bond is expressed
in -kcal/mole, the energy released upon bond formation. Consider bond formation
between two atoms: A + B --> A:B. The concentrations of the unbonded reactants
and the bonded products at equilibrium defines K(eq): K(eq)=[A:B]/[A][B]. From
deltaG=-RTlnK(eq), we see that the greater the free energy released (in
negative kcal/mole) upon bond formation, the stronger the chemical bond
{i.e the greater K(eq) is}. The energy of bond formation (-deltaG) equals
the amount of energy required to break a given bond. A table that lists the
bond strengths (energies) of various chemical bonds follows:
|
Type of Bond |
Strength (kcal/mole) |
| Covalent | -50 to -100 |
| Ionic | -80 or -1 |
| Hydrogen | -3 to -6 |
| Van der Waals | -0.5 to -1 |
| Hydrophobic | -0.5 to -3 |