Covalent Bonding And Nomenclature Chemistry Worksheet Page 2
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6Dipole-Dipole Forces
Dipole-dipole forces of attraction exist between polar mole
cules.
•
Polar molecules contain uneven distributions of charge.
o
The negat
ive dipole of one molecule is attracted to the positive dipole of another
o
molecule.
Example of Dipole-Dipole Forces - HCl
•
HCl is a polar molecule. The hydrogen end of the molecule forms the positive dipole
because it has the lower electronegativity. The chloride end of the molecule forms
the negative dipole because it has the higher electronegativity. The chlorid
e end of
the molecule is attracted to the hydrogen end of a neighboring molecule.
δ+
δ-
δ+
δ-
H
−Cl
H Cl
−
Dipole-dipole forces
↓
↓
↓
↓
↑
↑
↑
↑
C
l –H
Cl−H
δ+
δ-
δ+
δ-
Dipole-dipole fo
rces of attraction are stronger than London dispersion forces.
•
Hydrogen-Bonding
Hydrogen-Bonding is a special type of dipole-dipole force. Since no
electrons are
•
shared or transferred, hydrogen bonding is not a chemical bond.
Hydrogen bonding exists between where the very electronegative elements of
•
nitrogen, oxygen and fluorine are covalently bonded to hydrogen. Hydrogen bond
ing
occurs between
hydrogen and the unbonded electron pairs of nearby N, O, or F
molecules.
Examples of hydrogen bonding.
•
Hydrogen bonding
occurs in pure substances. The hydrogen bonding is
o
repr
esented by a dotted line.
H
H
H
O
H O
H
N
H
H F
N
H F
H
H
H
H
water
amm
onia
hydrogen fluoride
Hydrogen bonding can also occur in mixtures.
o
H
H
H
H F
O
H
H N
N
H
H
H
hydrogen fluoride and ammonia
water and ammonia
Hydrogen bonding is about ten times stronger than ordinary di
pole-dipole forces.
•
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