Hydrogen bond: A hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen (H) atom covalently bound to a highly electronegative atom. Example: Nitrogen (N), Oxygen (O), or Fluorine (F). These elements experiences the electrostatic field of another highly electronegative atom nearby. Note: 1) It stronger than a van der Waals interaction, but weaker than covalent or ionic bonds. 2)This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins. 3)The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.