Slides 1 16 Presentation

1
Slides 1 16 Presentation Slides 17 26 To be
printed as a handout Slides 4 and 14 are intended
to be short discussion activities for small groups
J Hudson 2005
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Chemical Ideas 5.4 Hydrogen Bonding
J Hudson 2005
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Electronegativity
An atom or ions electronegativity is its ability
to pull electrons towards itself in a covalent
bond. The most electronegative elements are
found towards the top right corner of the
periodic table.
4
Electronegativity
Which covalent bonds would be the most polar?
5
Hydrogen Bonding
The three types of bonds which give molecules
significant hydrogen bonding are (i) N H (ii)
O H (iii) F H

• These three bonds all have
• A strong permanent dipole
• A hydrogen atom
• An atom with lone pair electrons

6
H2O
H2Te
H2Se
H2S
SnH4
GeH4
SiH4
CH4
7
Hydrogen Bonding
Hydrogen bonding in water results in some unusual
properties

• Higher than expected boiling point
• High specific heat capacity
• (absorbs a lot of heat energy with only a
  small change in temperature)
• Ice is less dense than water

8
This section of water is frozen
This section of water is liquid
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The ice structure has large empty spaces which
gives it a lower density than water.
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Hydrogen Bonding in Hydrogen Fluoride
..
..
..
Fluorine atoms have three electron lone pairs for
bonding to other HF molecules
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Hydrogen Bonding in Hydrogen Fluoride
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Ice
Both lone pairs are involved in hydrogen bonds
Both hydrogen atoms are involved in hydrogen bonds
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Comparing Bonds
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Properties
How do these two molecules differ in boiling
point, viscosity and water solubility? Explain
why
Ethanol MR 46
Propane MR 44
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Physical Properties of Alcohols
Alcohol molecules can hydrogen bond to each other
and to water molecules. This explains their
solubility in water.
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Results of Hydrogen Bonding

• Wool and nylon fibres can hydrogen bond to water
  these fabrics can absorb water
• Polythene has no hydrogen bonding polythene
  clothes would get very sweaty and sticky
• Ice floats on water making life possible

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Chemical Ideas 5.4 Hydrogen Bonding
An atom or ions electronegativity is its ability
to pull electrons towards itself in a covalent
bond. The most electronegative elements are
found towards the top right corner of the
periodic table.
18
Hydrogen Bonding
The three types of bonds which give molecules
significant hydrogen bonding are (i) (ii)
(iii)

• These three bonds all have
• A strong permanent dipole
• A hydrogen atom
• An atom with lone pair electrons

19
Boiling Point (K)
20
Hydrogen Bonding
Hydrogen bonding in water results in some unusual
properties

• Higher than expected boiling point
• High specific heat capacity (absorbs a lot of
  heat energy with only a small change in
  temperature)
• Ice is less dense than water

21
The ice structure has large empty spaces which
gives it a lower density than water.
22
Hydrogen Bonding in Hydrogen Fluoride
Fluorine atoms have three electron lone pairs for
bonding to other HF molecules
23
Ice
Both lone pairs are involved in hydrogen bonds
Both hydrogen atoms are involved in hydrogen bonds
24
Comparing Bonds
25
Properties
How do these two molecules differ in boiling
point, viscosity and water solubility? Explain
why
Ethanol MR 46
Propane MR 44
26
Results of Hydrogen Bonding

• Wool and nylon fibres can hydrogen bond to water
  these fabrics can absorb water
• Polythene has no hydrogen bonding polythene
  clothes would get very sweaty and sticky
• Ice floats on water making life possible