Transcript 10.4_Attractive_Forces

Chapter 10 Structures of Solids
and Liquids
10.4
Attractive Forces between
Particles
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1
Ionic Bonds
In ionic compounds, ionic bonds
• are strong attractive forces
• hold positive and negative ions together
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2
Dipole-Dipole Attractions
In covalent compounds, polar
molecules
• exert attractive forces called
dipole-dipole attractions
• form strong dipole attractions
called hydrogen bonds between
hydrogen atoms bonded to F, O,
or N, and other atoms that are
strongly electronegative
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3
Dipole-Dipole Attractions
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4
Dispersion Forces
Dispersion forces are
• weak attractions between nonpolar molecules
• caused by temporary dipoles that develop when
electrons are not distributed equally
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5
Comparison of Bonding and Attractive Forces
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6
Mass and Boiling Points
Nonpolar covalent compounds such as alkanes family have
higher boiling points as
• the mass of the compounds increases
• Because more dispersion forces form
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7
Melting Points and Attractive Forces
• Ionic bonds require large amounts of energy to break apart.
Ionic compounds have very high melting points.
• Hydrogen bonds are the strongest type of dipole-dipole
attractions. They require more energy to break than other
dipole attractions. Compounds with hydrogen bonds have
moderate melting points.
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8
Melting Points and Attractive Forces
(continued)
• Dipole-dipole attractions are weaker than hydrogen
bonds, but stronger than dispersion forces. They have
low to moderate melting points.
• Dispersion forces are weak and little energy is needed
to break them. Compounds with dispersion forces
have the lowest melting points.
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9
Melting Points
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10
Learning Check
Identify the major type of attractive force in each of the
following substances:
1) ionic bonds
2) dipole-dipole attractions
3) hydrogen bonds
4) dispersion forces
A.
B.
C.
D.
E.
NCl3
H2O
Br2
KCl
NH3
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11
Solution
Identify the major type of attractive force in each
of the following substances:
1) ionic bonds
2) dipole-dipole attractions
3) hydrogen bonds 4) dispersion forces
2
3
4
1
3
A. NCl3
B. H2O
C. Br2
D. KCl
E. NH3
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12
Learning Check
Identify the compound in each pair that has the higher
melting point. Explain.
A. NCl3 or NH3
B. HBr or Br2
C. KCl or HCl
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Solution
A. NH3 would have a higher melting point than NCl3 because the
hydrogen bonds in NH3 are stronger than the dipole-dipole
attractions in NCl3.
B. HBr would have a higher melting point than Br2 because the
dipole-dipole attractions in HBr are stronger than the dispersion
forces in Br2
C. KCl would have a higher melting point than HCl because the ionic
bonds in KCl are stronger than the dipole-dipole attractions in
HCl.
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14
Molecular Polarity
Polarity affects the intermolecular forces of
attraction.
– Melting points and Boiling points
– Solubilities: Like dissolves like
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polarity affect the melting point of a
molecule
• A more polar molecule will have a higher
melting point. A polar molecule will have a
strong dipole-dipole bond and will require
more energy to break that bond.
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