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Chemical Bonding Part 5
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Chemical Bonding Part 5
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Chemical Bonding Part 5Polarity of Bonds
• If a covalent bond is formed between similar atoms, the shared pair of electrons lies
almost at the centre of the bond and electron cloud is uniformly distributed around the
two atoms.
• Such/ a covalent bond is called a non-polar covalent bond.
• Homonuclear molecules like H2, O2, Cl2, etc. are examples of compounds which contain
non-polar bonds.
• On the other hand, if a covalent bond is formed between different atoms.
• then the shared pair is displaced towards the more electronegative atom causing greater
concentration of electron density around the more electronegative atom.
•
us
Thus. the more electronegative atom acquires a partial negative charge and the less
Pl
electronegative atom acquires a partial positive charge.
e
• Thus, a partial ionic character arises in the covalent bond and is called polar covalent
0) ac
bond.
45 i R
• For example. the covalent bond in HCl molecule is polar.
31 ar
13 ak
• The electronegativity of Cl and H are 3.0 and 2.1 respectively.
06 h
• Due to this electronegativity difference, the chlorine end of HCl molecule acquires a
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partial negative charge
• (-)and hydrogen end has partial positive charge (+).
− ⎯ +
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𝐻 𝐶𝑙
a
• Such molecules with partial ionic character are called polar molecules. The molecules
im
like HF, HBr. BrCl, H2O etc. are also polar molecules.
ah
M
, Dipole moment- A measure of degree of polarity
• The degree of polarity in a covalent bond is expressed in terms of dipole moment () .
• It is defined as the product of magnitude of charge (e) developed on any of the atom
and the distance (d) between the atoms in the covalent bond.
• Thus, = e.d
• The unit of dipole moment is debye (D) and ID = 3.33564 x 10-30Cm.
• us
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It is a vector quantity as it has direction as well as magnitude.
e
• Dipole moment is usually indicated by an arrow, having +Sign on the tail (→).
0) ac
• It is written above the molecule with the arrow pointing towards the negative end.
45 i R
e.g.
31 ar
13 ak
• - → +
06 h
• H ⎯ Cl
Sa
• For a diatomic molecule, the dipole moment of the molecule is the same as that of
the bond.
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• Homoatomic molecules like H2, O2, Cl2 and N2 have zero dipole moment i.e., they are
a
im
non-polar.
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• On the other hand. a molecule like HF has a large dipole moment (1.91 D) due to the
high electronegativity of fluorine.
M
• Greater the electronegativity difference between the atoms. more will be dipole
moment.
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