Such bonds form between two ions by attraction of opposite charges rather like the poles of magnets. Hydrophobic associations are not true bonds . When surrounded by hydrophilic molecules, such as water, hydrophobic molecules are repelled and associate with each other. For example, the lipid bilayer of cell membranes is pushed to the interior of the membrane and away from water. Similarly, hydrophobic regions of proteins will face away from hydrophilic molecules.
Strong bonds are relatively inflexible, so weak bonds, such as hydrogen bonds.
Hydrogen bonds act as weak bridges or stabilizing attractive forces between or within molecules. Hydrogen bonds are very important in living systems, allowing flexibility while maintaining conformation. They exist when a hydrogen covalently bonded to an oxygen or nitrogen atom is attracted to another hydrogen or nitrogen within a polar molecule. This is particularly critical in the case of enzymes as their shape, particularly of the active site, dictates their function. If a protein is denatured by heat or chemical means it will lose its shape but more importantly it will loose its activity.