In 1920 Latimer and Rodebush introduced the idea of "hydrogen bond" to explain the nature of association in liquid state of substances like water, hydrogen fluoride, ammonia and formic acid, etc. In a hydrogen compound, when a hydrogen atom lies between two atoms having high electronegativities, it shows a unique property of forming a bond or a bridge between them, holding one of the atoms by a covalent bond and other by purely electrostatic forces (dipole-dipole attraction). This chemical combination between highly electronegative atoms of small atomic radius, such as F and N through a hydrogen bond is referred to as Hydrogen bond or Hydrogen bridge.
Hydrogen bond is defined as "an electrostatic attractive force between the. covalent bonded hydrogen atom of one molecule and an electronegative atom (such as F, 0, N) of the 'other molecule
Nature and Importance of Hydrogen Bonding
(i) Hydrogen bond is merely an electrostatic force rather than a chemical bond.
(ii) Hydrogen bond never involves more than two atoms.
(iii) Bond energy of hydrogen bond is in the range of 3 to 10 Kcal/mol or 10 to 40 kJ/moI, i. e., about 1/10th the energy of a covalent bond. .
(iv) With the increase of electronegativity of the atom to which hydrogen is covalently linked, the strength of' the hydrogen bond increases.
(v) All the three atoms in X -H- - -X lie in a straight line.
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