Hydrogen bonding in liquids

1. Presented by
Dr. Neelam
Department of chemistry

2. HYDROGEN BOND
Definition : It is an electrostatic attractive force between covalently
bonded hydrogen atom of one molecule and an electonegative atom (F, O,
N)
Main condition for H-bonding : -
(I) H should be covalently bonded with high electronegative element
like F, O, N
(II) Atomic size of electronegative element should be small.
(III) lone pair must be present.
Hydrogen bonding occurs in HCN, due to (-CN) triple bond (sp
hybridisation), electro negativities of carbon and nitrogen increases.
H F-----------H F--------H F

4. (A) Intermolecular H-bond
H-bond formation between two or more molecules of either the same or
different compounds known as Inter molecular H-bonding
These are two types.
(i) Homo intermolecular :- H-bond between molecules of same
compounds.
eg.
(ii) Hetro intermolecular :- H-bond between molecules of different
compounds.
eg. alcohol, water

5. (B) Intra molecula H-bond :- It takes place within the molecule.
(i) H-bonded with electronegative elements of a functional group, form H-
bond with another electronegative element present on nearest position
on the same molecule.
(ii) This type of H-bond is mostly occurred in organic compounds.
(iii) It result in ring formation (Chelation).
eg.

6. Properties inter molecular H-
bonding
intra molecular H-
bonding
Boiling point In inter molecular H-
bonding molecular
contain Vander-Waal
bonding with H-bonding
In intra molecular H-
bonding molecular
contain Vander-Waals
bonding only
Solubility Increase solubility in
water.
decrease the solubility
in water

7. Properties inter
molecular H-
bonding
intra
molecular H-
bonding
Acidic nature Increase acidic
character
decrease acidic
character
viscosity Increase decrease

8. Physical state Due to hydrogen
bonding H2O is liquid
Due to not present in
hydrogen bond H2S is
gas.
Melting point
(H-bond)
H2O > NH3 > HF
4 4 2
E.N. = F > O > N
(stronger H-bonding
NH3 in solid than liquid)
Boiling point H2O > HF > NH3
4 2 4
(stronger H-bonding HF
in liquid or gaseous state
than in solid )

9. Boiling point ∝ molecular mass ∝ vanderwaal force
boiling point: HF < H Cl < HBr < HI HCl < HBr < HI < HF
boiling point: H2O < H2S < H2Se < H2Te H2S < H2Se < H2Te < H2O
BOND STRENGTH ∝ H-bonding ∝ E.N. of A ∝ E.N. of B
1
A H -------- B
H-bondE.N. atom E.N. atom
(a) O H------O (b) O H------N
(c) N H------N (d) N H------O
Which has more strength of H-bond

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