1- Covalent Bonds Molecules are formed by sharing of electrons between atoms.Hydrogen bonds result from electrostatic attraction between an electro-negative atom and a hydrogen atom
that is bonded covalently to a second electronegative atom.2- Ionic Bonds or Electrostatic Bonds Ionic bonds result from the electrostatic attraction between two ionized groups of opposite charges.Common examples of such compounds include NaCl, KBr and NaF.4- Hydrophobic Interactions These are formed by interactions between nonpolar hydrophobic side chains by eliminating water molecules.