Chapter 6 Chemical bonding
and molecular shapes
How atoms connect to one another?
6.1 An atomic model is needed to
understand how atoms bond
Electrons in the outermost occupied shell of any atom
are responsible for the atom’s chemical properties.
The electrons that participate in chemical bonding are
called valence electrons (价电子 ),the shell they
occupy is called the valence shell (价层 ) of an atom.
Valence electrons can be conveniently represented as a
series of dots surrounding an atomic symbol.
(Electron-dot structure or Lewis dot symbol).
Valance electrons can be either paired or unpaired.
Paired electrons usually do not form chemical bonds
with other elements.
? ?
?Cl? ?
? ?
?C?
?
?
Unpaired
electronsUnpaired electronPaired
electrons
Chlorine Carbon
6.2 Atoms can lose or gain electrons to
become ions (离子 )
When the number of protons in the
nucleus of an atom equals to the
number of electrons in the atom,
the charges balance and the atom
is electrically neutral,If one or
more electrons are lost or gained,
the atom takes on a net electric
charge,Any atom having a net
electric charge is called an ion,If
the electrons are lost,the ion’s net
charge is positive,If the electrons
are gained,the ion’s net charge is
negative.
Na 11 protons11 electrons
Na+ 11 protons10 electrons
Cl 17 protons17 electrons
Cl- 17 protons18 electrons
Shell model can be used to deduce the type of
ion an atom tends to form,Atoms tend to
lose or gain electrons so that they end up
with an outermost occupied shell that is
filled to capacity.
1+ 2+ 3+ 4- 3- 2- 1- 0
6.3 Ionic bonds result from a transfer of
electrons
When an atom that tends to lose electrons is
placed in contact with an atom that tends to
gain them,the result is that an electron
transfer and the formation of two oppositely
charged ions,The two oppositely charged
ions are thus attracted to each other by the
electric force,which holds them together.
This electric force of attraction between two
oppositely charged ions is called an ionic
bonds (离子键 ),All compounds containing
ions are referred to as ionic compounds (离
子化合物 ).
How to judge the composition of an
ionic compound? Balance of electric
charge
Ruby
Sapphire
6.4 Covalent bonds result from a
sharing of electrons
The electrical attraction in
which atoms are hold
together by their mutual
attraction for shared
electrons is called an
covalent bond (共价键 ),A
compound composed of
atoms held together by
covalent bonds is a
covalent compound (共价
化合物 ).
F F+
7e- 7e-
F F
8e- 8e-
More than one electron can be shared in an atom,double
bond (双键 ) and triple bond (叁键 ).
O C O
double bonds
N N
triple bond
F F
single covalent bond
6.5 Valence electrons determine
molecular shape
How to determine the three
dimensional structure of
a covalent compound?
Valence shell electron-pair
repulsion (VESPR),any
given pair of valence-
shell electrons strives to
get as far away as
possible from all other
electron pairs in the
shell.
6.6 Polar covalent bonds result from an
uneven sharing of electrons
What is the distribution of a
shared pair of electrons in
a covalent bond?
In HF the shared electrons
are drawn more close to F
atom,so the fluorine side
of bond is electrically
negative while the
hydrogen side of bond is
electrically positive,This
kind of charge separation
is called a dipole (偶极 ).
In H2,evenly shared
in HF,unevenly shared
The ability to draw bonding
electrons is decided by the atom’s
electronegativity (电负性 ).
Polar bond and nonpolar bond?
When the two atoms have the same electronegativity,
no dipole is formed and the bond is called a nonpolar
bond (非极性键 ).
When the two atoms have the different electronegativity,
a dipole is formed and the bond is called a polar
bond (极性键 ).
H F
electron rich
regionelectron poorregion
d+ d-C, C
6.7 Molecular polarity results from an
uneven distribution of electrons
If all bonds in a molecule are nonpolar,the
molecules as a whole is also nonpolar,(H2,O2)
If a molecule consists of polar bonds,the polarity
of the molecule is decided by the polarity of the
bonds and also the shape of the molecule.
The molecular polarity decides a lot of
the physical properties of substances
Substance Boiling Point(℃ )
Polar
Hydrogen 20
Water,H2O 100
Ammonia,NH3 -33
Nonpolar
Oxygen,O2 -183
Hydrogen,H2 -253
Nitrogen,N2 -196
Carbon dioxide,CO2 -79
Table6.2 Boiling Points of some polar and nonpolar
substance
Chapter 7 Molecular Mixing
Water that has been fully aerated at room
temperature,contains only 1 oxygen molecule
for every 200,000 water molecules,Why?
The attractive forces between water
molecules and oxygen molecules are very
weak,
7.1 Submicroscopic particles electrically
attract one another
Four types of interaction between ions,molecules and
atoms (submicroscopic particles)
Attraction Relative strength
Ion-dipole Strongest
Dipole-dipole
Dipole-induced dipole (诱导偶极 )
Induced dipole-induced dipole weakest
The molecular-molecular interaction
determines many of properties of substance
Ion- dipole interaction,table salt dissolved in water
Dipole-dipole interaction
An unusually strong dipole-
dipole attraction,hydrogen
bond (氢键 ) (occurs between
hydrogen atom covalently
bonded to a highly
electronegative atom,usually
nitrogen,oxygen and
fluorine)
The hydrogen bond is
responsible for many of the
unusual properties of water
and many of biomolecules,
such as DNA,
Hydrogen Bond
Dipole-induced dipole interaction
oxygen dissolved in water,carbon dioxide in water
Isolated oxygen molecule
Induced dipole-induced dipole interaction
(dispersion force,色散力 )
Iodine,I2,a solid at
room temperature
Fluorine,F2,a gas at
room temperature
Fluorine-containing molecules
usually have very small induced
dipole,and thus have very weak
interaction with other molecules
7.2 A solution is a single-phase
homogeneous mixture
Solution can be solid,liquid and gaseous
Solid,ruby (red chromium compounds in aluminum oxide)
Blue sapphire (green iron compounds and blue titanium compounds in aluminum oxide)
Metal alloys
Gaseous,air (breath in,78% nitrogen,21% oxygen,1% others)
(exhale,75% nitrogen,15% oxygen,5% carbon dioxide,6% water vapor)
Solvent (溶剂 ),Solute (溶质 ),Dissolving (溶解 )
How much a given solute can dissolve in a given solvent?
Unsaturated solution(不饱和溶液 ),Saturated solution (饱和溶液 )
Concentration (浓度 ) = amount of solute/amount of solvent
Concentration can be weight and molar
7.3 Solubility (溶解性 ) is a measure of
how well a solute dissolves
Solubility depends on attractions between
solute/solvent particles.
When the molecule-to-molecule attractions among
solute molecules are comparable to the molecule-
to-molecule attractions among solvent molecules,
the result can be no practical point of saturation,as
in the case of ethanol/water,Ethanol and water
can mix homogeneously in any proportion,
(infinitely soluble)
Solubility changes with temperature
100℃ 20℃
180g NaNO3 in
100ml water
87g NaNO3 in
100ml water
93g of
NaNO3
precipitates
out of
solution
Gases are more soluble
at low temperature and
high pressure
Nonpolar gases readily
dissolve in
perfluorocarbons:
Oxygen has much
higher solubility in
perfluorocarbons than
in air,This has many
applications.
7.4 Soap works by being both polar and
nonpolar
grime = dirt + grease
Grime is difficult to remove from
hands or clothing using just water,
because grime is nonpolar and
water is polar,Grime can be
dissolved and washed away by
nonpolar substances such as
trichloroethane.
Grime can also be washed away
by soap and water,such soap is a
substance having both polar and
nonpolar properties.
Detergents
Calcium and magnesium ions in hard water can replace the sodium ions in
soap to form insoluble substances,Sodium carbonate is usually added
to detergent as a water-softening agent,
Treat with
NaOH
Fat molecule Three fatty acid soap molecules Glycerol molecule
and molecular shapes
How atoms connect to one another?
6.1 An atomic model is needed to
understand how atoms bond
Electrons in the outermost occupied shell of any atom
are responsible for the atom’s chemical properties.
The electrons that participate in chemical bonding are
called valence electrons (价电子 ),the shell they
occupy is called the valence shell (价层 ) of an atom.
Valence electrons can be conveniently represented as a
series of dots surrounding an atomic symbol.
(Electron-dot structure or Lewis dot symbol).
Valance electrons can be either paired or unpaired.
Paired electrons usually do not form chemical bonds
with other elements.
? ?
?Cl? ?
? ?
?C?
?
?
Unpaired
electronsUnpaired electronPaired
electrons
Chlorine Carbon
6.2 Atoms can lose or gain electrons to
become ions (离子 )
When the number of protons in the
nucleus of an atom equals to the
number of electrons in the atom,
the charges balance and the atom
is electrically neutral,If one or
more electrons are lost or gained,
the atom takes on a net electric
charge,Any atom having a net
electric charge is called an ion,If
the electrons are lost,the ion’s net
charge is positive,If the electrons
are gained,the ion’s net charge is
negative.
Na 11 protons11 electrons
Na+ 11 protons10 electrons
Cl 17 protons17 electrons
Cl- 17 protons18 electrons
Shell model can be used to deduce the type of
ion an atom tends to form,Atoms tend to
lose or gain electrons so that they end up
with an outermost occupied shell that is
filled to capacity.
1+ 2+ 3+ 4- 3- 2- 1- 0
6.3 Ionic bonds result from a transfer of
electrons
When an atom that tends to lose electrons is
placed in contact with an atom that tends to
gain them,the result is that an electron
transfer and the formation of two oppositely
charged ions,The two oppositely charged
ions are thus attracted to each other by the
electric force,which holds them together.
This electric force of attraction between two
oppositely charged ions is called an ionic
bonds (离子键 ),All compounds containing
ions are referred to as ionic compounds (离
子化合物 ).
How to judge the composition of an
ionic compound? Balance of electric
charge
Ruby
Sapphire
6.4 Covalent bonds result from a
sharing of electrons
The electrical attraction in
which atoms are hold
together by their mutual
attraction for shared
electrons is called an
covalent bond (共价键 ),A
compound composed of
atoms held together by
covalent bonds is a
covalent compound (共价
化合物 ).
F F+
7e- 7e-
F F
8e- 8e-
More than one electron can be shared in an atom,double
bond (双键 ) and triple bond (叁键 ).
O C O
double bonds
N N
triple bond
F F
single covalent bond
6.5 Valence electrons determine
molecular shape
How to determine the three
dimensional structure of
a covalent compound?
Valence shell electron-pair
repulsion (VESPR),any
given pair of valence-
shell electrons strives to
get as far away as
possible from all other
electron pairs in the
shell.
6.6 Polar covalent bonds result from an
uneven sharing of electrons
What is the distribution of a
shared pair of electrons in
a covalent bond?
In HF the shared electrons
are drawn more close to F
atom,so the fluorine side
of bond is electrically
negative while the
hydrogen side of bond is
electrically positive,This
kind of charge separation
is called a dipole (偶极 ).
In H2,evenly shared
in HF,unevenly shared
The ability to draw bonding
electrons is decided by the atom’s
electronegativity (电负性 ).
Polar bond and nonpolar bond?
When the two atoms have the same electronegativity,
no dipole is formed and the bond is called a nonpolar
bond (非极性键 ).
When the two atoms have the different electronegativity,
a dipole is formed and the bond is called a polar
bond (极性键 ).
H F
electron rich
regionelectron poorregion
d+ d-C, C
6.7 Molecular polarity results from an
uneven distribution of electrons
If all bonds in a molecule are nonpolar,the
molecules as a whole is also nonpolar,(H2,O2)
If a molecule consists of polar bonds,the polarity
of the molecule is decided by the polarity of the
bonds and also the shape of the molecule.
The molecular polarity decides a lot of
the physical properties of substances
Substance Boiling Point(℃ )
Polar
Hydrogen 20
Water,H2O 100
Ammonia,NH3 -33
Nonpolar
Oxygen,O2 -183
Hydrogen,H2 -253
Nitrogen,N2 -196
Carbon dioxide,CO2 -79
Table6.2 Boiling Points of some polar and nonpolar
substance
Chapter 7 Molecular Mixing
Water that has been fully aerated at room
temperature,contains only 1 oxygen molecule
for every 200,000 water molecules,Why?
The attractive forces between water
molecules and oxygen molecules are very
weak,
7.1 Submicroscopic particles electrically
attract one another
Four types of interaction between ions,molecules and
atoms (submicroscopic particles)
Attraction Relative strength
Ion-dipole Strongest
Dipole-dipole
Dipole-induced dipole (诱导偶极 )
Induced dipole-induced dipole weakest
The molecular-molecular interaction
determines many of properties of substance
Ion- dipole interaction,table salt dissolved in water
Dipole-dipole interaction
An unusually strong dipole-
dipole attraction,hydrogen
bond (氢键 ) (occurs between
hydrogen atom covalently
bonded to a highly
electronegative atom,usually
nitrogen,oxygen and
fluorine)
The hydrogen bond is
responsible for many of the
unusual properties of water
and many of biomolecules,
such as DNA,
Hydrogen Bond
Dipole-induced dipole interaction
oxygen dissolved in water,carbon dioxide in water
Isolated oxygen molecule
Induced dipole-induced dipole interaction
(dispersion force,色散力 )
Iodine,I2,a solid at
room temperature
Fluorine,F2,a gas at
room temperature
Fluorine-containing molecules
usually have very small induced
dipole,and thus have very weak
interaction with other molecules
7.2 A solution is a single-phase
homogeneous mixture
Solution can be solid,liquid and gaseous
Solid,ruby (red chromium compounds in aluminum oxide)
Blue sapphire (green iron compounds and blue titanium compounds in aluminum oxide)
Metal alloys
Gaseous,air (breath in,78% nitrogen,21% oxygen,1% others)
(exhale,75% nitrogen,15% oxygen,5% carbon dioxide,6% water vapor)
Solvent (溶剂 ),Solute (溶质 ),Dissolving (溶解 )
How much a given solute can dissolve in a given solvent?
Unsaturated solution(不饱和溶液 ),Saturated solution (饱和溶液 )
Concentration (浓度 ) = amount of solute/amount of solvent
Concentration can be weight and molar
7.3 Solubility (溶解性 ) is a measure of
how well a solute dissolves
Solubility depends on attractions between
solute/solvent particles.
When the molecule-to-molecule attractions among
solute molecules are comparable to the molecule-
to-molecule attractions among solvent molecules,
the result can be no practical point of saturation,as
in the case of ethanol/water,Ethanol and water
can mix homogeneously in any proportion,
(infinitely soluble)
Solubility changes with temperature
100℃ 20℃
180g NaNO3 in
100ml water
87g NaNO3 in
100ml water
93g of
NaNO3
precipitates
out of
solution
Gases are more soluble
at low temperature and
high pressure
Nonpolar gases readily
dissolve in
perfluorocarbons:
Oxygen has much
higher solubility in
perfluorocarbons than
in air,This has many
applications.
7.4 Soap works by being both polar and
nonpolar
grime = dirt + grease
Grime is difficult to remove from
hands or clothing using just water,
because grime is nonpolar and
water is polar,Grime can be
dissolved and washed away by
nonpolar substances such as
trichloroethane.
Grime can also be washed away
by soap and water,such soap is a
substance having both polar and
nonpolar properties.
Detergents
Calcium and magnesium ions in hard water can replace the sodium ions in
soap to form insoluble substances,Sodium carbonate is usually added
to detergent as a water-softening agent,
Treat with
NaOH
Fat molecule Three fatty acid soap molecules Glycerol molecule
