Types of Chemical Bonds
IONIC BONDS
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Occur between an element with low
ionization energy (a metal) and an element
with high ionization energy (a non-metal).
An actual transfer of electrons from the
metal (becoming a cation) to the non-metal
(becoming an anion) occurs.
This transfer results in the formation of 2
oppositely charged ions.
The electrostatic interaction between the
2 ions holds the compound together.
Properties of Ionic Compounds
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Solids at room temperature because the
cumulative attraction of the ions is very strong.
The intra-forces are the same as the inter- forces
(i.e. the electrostatic attraction of oppositely
charged ions)
Atoms are arranged in a highly ordered crystal
lattice structure which maximizes the attractive
forces between oppositely charged ions and
minimizes the repulsion between like charged ions
(the crystal structures are determined
experimentally using X-ray crystallography).
Soluble in water (the ions will dissociate in water).
Will conduct electricity as a liquid or aqueous
solution because the ions are free to move to
oppositely charged electrodes.
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COVALENT BONDS
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Occur between 2 atoms with high ionization energies
(i.e. 2 non-metal atoms).
Result from a sharing of electrons to obtain a full
outer energy level (octet rule).
If the electronegativity difference between the two
atoms is less than 0.5, the bond is a true covalent bond
and the electrons are shared equally.
If the electronegativity difference between the two
atoms is between 0.5 and 1.6, the bond is polar and
there is an unequal sharing of electrons.
If the electronegativity difference between the two
atoms is 1.7 or higher, the bond is ionic.
If a molecule contains polar covalent bonds and is
asymmetrical, the molecule will be polar.
If both electrons being shared come from the same
atom, the bond is a coordinate covalent bond.
Properties of Non-Polar Covalent
Compounds
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Have low melting and boiling points and are
usually gases at room temperature. This is
due to the low intermolecular forces that
exist in these molecules (London Dispersion
Forces only).
If solid at room temperature, the solid is
usually soft and waxy.
Soluble in non-polar solvents such as
ethers.
Will not conduct electricity in any form due
to the fact that there are no ions present.
Properties of Polar Covalent Molecules
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Since these compounds exhibit polarity or
dipoles, their intermolecular forces will be
greater than non-polar covalent compounds (the
presence of dipole-dipole forces and possibly Hbonding).
These compounds will have higher melting and
boiling points and are more likely to be liquids or
solids at room temperature (may even exhibit a
crystal lattice like sugar).
Will dissolve in polar solvents if H-bonding is
present (sugar in water).
Will not conduct electricity to any appreciable
degree (only ionize to a very small degree)
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Intermolecular Forces Summary
3 types of bonding forces between molecules:
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1) Dipole-Dipole Forces:
Only among polar molecules where partial +ve of one end will
attract partial –ve of other molecule. The stronger the polarity,
the stronger the dipole-dipole force.
2) London Dispersion (all molecules)
Attraction of +ve nuclei of nearby molecules on –ve electrons of a
molecule. Generally weak force, increases with the number of
atoms in a molecule.
3) Hydrogen Bonds:
Occurs among molecules with H bonded to high electronegative
atoms (N, O, F). Type of very strong dipole force, where H+ is
attracted to unpaired e-. MUST have at least one lone pair of
electrons
Properties of liquids depend on
intermolecular forces…
Boiling Points
Solubility
 Surface tension
 Volatility
 Shape of meniscus
 Capillary action
 Density in solid form
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Metallic Bonding
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What is a metallic bond ?
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Occurs when both atoms have low
ionization energies and low
electronegativities and will lose electrons
easily (i.e. 2 metals)
In metallic bonding, positive metal ions are
arranged with valence electrons delocalized
around them.
Since the electrons are delocalized, they
are mobile and able to move throughout the
metal structure.
e-
e-
e
-
e-
e
Properties of Metallic Compounds
1.
2.
3.
4.
5.
Malleable and ductile because atoms are
not restricted to one position by a fixed
bond and the ions can roll past each
other.
Good conductors of heat and electricity
because the electrons are mobile and can
transmit energy rapidly.
Shiny because when light strikes a metal,
the valence electrons absorb energy,
oscillate at the same frequency as the
incident light (incoming light) and then
emit light as a reflection of the original
light.
Solids at room temperature (except mercury)
due to the strong bonds (intermolecular and
intramolecular forces are the same).
They exhibit the photoelectric effect which is
electron emission caused by heat or light. This
occurs when the frequency and therefore the
energy of light striking a metal is sufficient to
overcome the attractive forces and an electron
escapes the metal decreasing the energy of the
photon.
metal
electrons escaping the
surface of the metal
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What is a network solid?
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Network solids are macromolecules, giant
structures of covalently bonded atoms in
one, two or three dimensional arrays.
Allotropes: elements that exist in
different physical forms with different
physical properties but the same chemical
properties.
For example graphite and diamond are
allotropes of carbon (as is “Buckey ball”).
Both form carbon dioxide and water when
undergoing combustion but only graphite
conducts electricity and diamond is one of
the hardest substances known.
3-Dimensional Network Solids
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These network solids consist of covalently
bonded atoms which form regular 3-D
arrays or crystals.
Much like an ionic crystal, the
intermolecular bonds are the same as the
intramolecular bonds (covalent bonds).
Due to the very strong bonds, these solids
will have very high melting and boiling
points, will be solids at room temperature,
be extremely hard, not soluble in polar or
non-polar solvents and they do not conduct
electricity.
Examples include diamond, quartz and
silicon carbide.
Diamond
C
C
C
C
C
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3-dimensional array of carbon atoms covalently
bonded in a tetrahedral arrangement.
Strong covalent bonds give diamond its hardness.
There are no delocalized electrons, therefore
diamond will not conduct electricity.
There are several planes of atoms within the
crystal and diamonds are cut along these planes.
Light is reflected by these planes to give
diamonds their sparkle (total internal
refraction).
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Covalent Network Crystals
Hard, brittle at room temp
 Very high melting points (higher than
ionic or molecular crystals)
 Non conductive
 Insoluble
 Examples include diamond, quartz,
silicon carbide
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Network Solids of Silicon
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1.
Silicon makes up 25.7 % of the Earth’s crust.
Quartz
• A large 3-dimensional network with silicon and
oxygen.
• Each silicon is tetrahedrally bonded to four
oxygen atoms.
• Foreign metal ions in quartz produce
semiprecious stones such as emerald, amethyst
and garnet.
O
O
O
Si
O
O
Si
O
O
O
Si
O
O
Quartz-silicates
Covalent crystals
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2-Dimensional Network Solids
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Networks which form 2-D arrays or
sheets.
Within a sheet the atoms are held
together with covalent bonds.
Weak van der Waals forces hold the layers
together.
These solids will also have high melting and
boiling points however they will be soft and
the layers will slide over each other
allowing them to be used as a lubricant.
An example of this type of solid is
graphite.
Graphite
C
C
120°
C
C
C
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C
C
C
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C
C
C
C
Graphite is a 2-dimensional array of carbon atoms
arranged in layers of hexagons.
The electrons making up the “double bonds” are
actually delocalized throughout the structure (i.e.
not true double bonds)
The layers of hexagons are held in place by van
der Waals forces (intermolecular forces).
Graphite is soft, slippery and is used as a
lubricant because the layers can slide past
each other.
The delocalized electrons give stability to
graphite.
The delocalized electrons are able to move
freely therefore allowing graphite to
conduct electricity.
When you write with a pencil you are
breaking of layers of the graphite.
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Diamond : 3D Carbon
Graphite:
2D Carbon
1-Dimensional Network Solids
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2.
These are solids that form networks in a
one dimensional array or fibre.
They consist of long chains held together
by covalent bonds.
The forces between adjacent chains are
very weak therefore the solids will form
threads.
They have very high melting and boiling
points due to the strong covalent bonds.
They are solids at room temperature and
are not soluble in water.
An example of this type of solid is
asbestos.
Mica
• 2-dimensional sheets of silicate
• Weak attractions between the layers
make mica flake easily
O Si
2-
O
Si
O
Si
O Si
3. Asbestos
• Asbestos forms fibrous, stringy onedimensional chains.
• Can be used as a fire retardant but it is
now known to cause lung cancer
+2
O- Ca O-
Si O
Si
O
Si
O Si
O- Mg+2 O-
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