1. Covalent and ionic bonds
Through interaction with one another, atoms are able to achieve a more stable arrangement of electrons in the outermost shell of their nucleus. Ionic bonds are formed as electrons move from one atom to the next during the bonding process. The exchange of electrons between two atoms results in the formation of a covalent bond. In many cases, the formation of covalent bonds involves just a partial transfer of electrons, which results in an unequal distribution of electrons and a polar covalent bond.
At very short distances any two atoms show a weak bonding interaction due to their fluctuating electrical charges. If the two atoms are too close together, however, they repel each other very strongly. Each atom has a characteristic Van der Waals radius. The contact distance between any two atoms is the sum of their Van der Waals radii.
Van der Waals forces will attract two atoms until the distance between them equals the sum of their Van der Waals radii. Although they are very weak on their own, Van der Waals attractions can become significant when two macromolecular surfaces are very close together.
2. Hydrogen bonds
When a hydrogen atom is “sandwiched” between two electron-attracting atoms, hydrogen bonds form (usually oxygen or nitrogen). When three hydrogen atoms are in a straight line, hydrogen bonds are strongest.
Hydrogen bonds can be found in DNA and RNA. Three hydrogen bonds exist between G and C pairs, and two hydrogen bonds exist between A and T pairs. Hydrogen bonds also exist between amino acids in polypeptide chains.
Water molecules can establish hydrogen bonds with molecules that can make hydrogen bonds with one other. The hydrogen bonds established between two molecules dissolved in water are relatively weak due to competition with water molecules.
3. Weak chemical bonds
Short-range non-covalent forces are one way organic molecules can interact with one another. Chemical bonds that are just half as strong as covalent bonds are known as weak covalent bonds. However, when several of them are created simultaneously, they are strong enough to provide a tight bond.