Hydrogen bonding occurs when a hydrogen atom covalently bonded to an electronegative atom like nitrogen, oxygen or fluorine interacts with another electronegative atom. This interaction is stronger than van der Waals forces but weaker than covalent or ionic bonds. Hydrogen bonding plays a key role in the structures of water and DNA, enabling water to have high boiling and melting points and DNA to form its double helix structure. There are two types of hydrogen bonds: intermolecular between molecules and intramolecular within the same molecule.

1. Hydrogen bond is the attractive interaction of a
hydrogen atom with an electronegative atom , such
as nitrogen, oxygen or fluorine. That comes from
another molecular chemical group.
HYDROGEN BOND

2. Hydrogen must be covalently bonded with another
electronegative atom to create the bond.
These bonds can occur between molecules or with the
different parts of a single molecule .
Hydrogen bond is stronger than van der waals force
but weaker than covalent bond or ionic bond.
This types of bond occurs in both inorganic molecules
such as water and organic molecules such as DNA.

3. THERE ARE TWO TYPES OF HYDROGEN
BONDS :
INTERMOLECULAR HYDROGEN BOND
INTERAMOLECULAR HYDROGEN BOND
TYPES OF HYDROGEN BOND

4. This type of h-bond occurs when hydrogen
bonding is between hydrogen atom of one
molecule and an atom of the
electronegative element of another
molecule.
INTERMOLECULER H- BOND

5. Intermolecular example
 Hydrogen bond between the molecules of hydrogen fluoride.
 Hydrogen bond in or water molecules.

6. This type of h-bond occurs when hydrogen
bonding is between hydrogen atom
and an atom of the electronegative
element of same molecule.
INTERAMOLECULER H- BOND

7. Intramolecular example
 o-nitrophenol
 salicilaldehyde.

8. H-BOND IN WATER

9.  The most ubiquitous , and perhaps simplest example of a
hydrogen bond is found between water molecules.
 It can form a h-bond with other water molecules ,this can
go up to four h-bonding in with single molecule.
 Liquid waters high boiling point is due to high number of
h-bonds each molecule can form relative to its low
molecular mass.
 Owing to the difficulty of breaking these bonds water has
a very high boiling point, melting point and viscosity
compared to other similar liquids not conjoined by
hydrogen bonds.

10. H-BOND IN DNA

11.  Hydrogen bonding plays an important role in determining
the tree dimensional structures adopted by proteins and
nucleic bases.
 The double helical structure of DNA for example is due to
largely hydrogen bonding between the base pairs, which
links one complementary strand to the other and enable
replication

12. HISTORY
• In the book “the nature of the chemical bond.” Linus Pauling
credits T.S.Moore and T.F.Winmill with the first mention of the
hydrogen bond in 1912
• Moore and Winmill used the hydrogen bond to account for the
fact that trimethylammonium hydroxide is a weaker base than
tetramethylammonium hydroxide.
• The description of hydrogen bonding in its more well known
setting,water came some years later in 1920 from Latimer and
Rodebush