Bond polarity

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Bond polarity
R W Grime Ripon Grammar School
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Electronegativity the power of an atom to
attract the electrons in a covalent bond
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Factors affecting electronegativity
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1
H F
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Factors affecting electronegativity
1) Nuclear charge the more protons, the
stronger the attraction from the nucleus to the
bonding pair of electrons.
2) Atomic radius the closer the bonding
electrons to the nucleus, the stronger the
attraction from the nucleus to the bonding pair
of electrons.
3) Shielding the less shells of electrons
shielding (repelling) the bonding electrons, the
stronger the attraction from the nucleus to the
bonding pair of electrons.
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Factors affecting electronegativity
1) Nuclear charge more protons, stronger
attraction between nucleus and bonding pair of
electrons.
2) Atomic radius closer to the nucleus,
stronger attraction between nucleus and bonding
pair of electrons.
3) Shielding less shells of electrons between
the nucleus and the electrons, less shielding
(less repulsion), stronger attraction between
nucleus and bonding pair of electrons.
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Trend down a group
Electronegativity decreases

• Atomic radius increases
• More shielding
• ? Less attraction between nucleus and bonding
  pair of electrons

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Trend across a period
Electronegativity increases

• Atomic radius decreases
• More nuclear charge
• ? Stronger attraction between nucleus and bonding
  pair of electrons

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Formation of a covalent bond
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Non-polar bond
Polar bond
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Electronegativity Difference
0
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?-
?
X-
X
Y
X
Y
Y
X-
Y
Pure covalent
Polar ionic Distorted ions
Pure ionic
Polar covalent Electrons not equally shared
Polarisation of covalent bonds
Polarisation of ions
Favoured by small, highly charged ve ions, e.g.
Li, Be2
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Covalent bonding
Ionic bonding
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Difference in electronegativity decreases
ve ion gets smaller and more highly charged, so
ve polarised more
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Difference in electronegativity decreases
ve ion gets smaller and more highly charged, so
ve polarised more
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H2O
?-
O
H
H
?
?
Bonds polar
Molecule polar
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NH3
?-
N
H
H
?
?
H
?
Bonds polar
Molecule polar
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CO2
?
?-
?-
C
O
O
Bonds polar
Molecule non-polar
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CCl4
Bonds polar
Molecule non-polar
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