CHEMICAL BONDING
Overview
Bonding
Ionic
Covalent
Metallic
Structure
Giant
ionic
Simple
Giant
molecular covalent
Giant
Metallic
Example
Sodium
chloride
Water
Diamond
Iron
Bonding and structure explains the properties of a substance!
Physical & Chemical Properties




‘property’: ‘what something is like’
Physical properties of a substance are those that
can be observed or measured without the
substance changing into another substance.
Chemical properties of a substance describe the
change of a substance into another substance.
Some examples of physical properties:
Solubility in water
(or other solvents)
Melting and
boiling points
Electrical
conductivity
Ionic Bond: The Definition
An ionic bond…
is the force of attraction between
opppositely charged ions in a
compound.
Giant Ionic Structures
Physical Properties: M.P. & B.P.
Ionic compounds have high melting
and boiling points.


strong electrostatic forces of attraction between
the ions in an ionic compound
large amount of heat is needed to break the strong
ionic bonds holding the ions together
Giant Ionic Structures
Physical Properties: Electrical Conductivity
Ionic compounds do not conduct electricity in the
solid state. It conducts electricity
in the molten and aqueous state.
Why do ionic compounds only conduct electricity in the
molten or aqueous state, but not in the solid state?
 ions can move in the molten or aqueous state
 moving ions carry the electric current
Giant Ionic Structures
Physical Properties: Solubility
Ionic compounds are soluble in water
but insoluble in organic solvents.



ions attract water molecules
disrupts the crystal structure
cause the ions to separate and go into solution
Giant Ionic Structures
Physical Properties: Volatility
Ionic compounds are not volatile and
hence, have no smell.

cannot evaporate easily because of strong ionic
bonds holding the ions together
A volatile substance evaporates easily.
Giant Ionic Structures
Physical Properties: Physical State


Ionic compounds are hard, crystalline solids.
ions held in place by strong ionic bonds, make the
crystal hard
ions are arranged in straight rows and form
structure with flat sides, resulting in a crystalline
structure (flat sides &
regular shapes)
Compare and Contrast
Ionic VS Covalent

Similarities
 Electronic
configuration of a noble gas
(PS: Everybody wants to be noble!!)

Differences
Ionic Bond
Covalent Bond
Between positive ions of
metals and negative ions of
non-metals
Between non-metal
atoms
Electrons are transferred
Electrons are shared
What to do??
Covalent Bonding
Covalent Bond: The Definition
A covalent bond is…
a bond formed by the sharing of
a pair of electrons.
More about COVALENT BONDING

Each atom acquires a stable octet structure
 Electronic
configuration of noble gas (Full shell) =
Energetically stable

Formed between atoms of non-metals (but there
are exceptions!)
 “Spectrum” of bonds
Simple Molecular Substances

Consists of small molecules, e.g. bromine
Simple Molecular Substances

Within the molecule
Atoms are held together by strong
covalent bonds

Between molecules
Weak intermolecular forces (van der
Waals’ forces)
Iodine, I2
Within each iodine
molecule, the iodine
atoms are held together by
strong covalent bonds.
Between the iodine
molecules, there are
only weak van der
Waals’ forces holding
the molecules together.
Methane, CH4
In a molecule of methane,
CH4, the four C–H
covalent bonds are
strong.
However, weak intermolecular
forces between methane
molecules hold them together
loosely. Therefore, methane
exists as a gas at room
temperature and pressure.
Physical Properties

Physical state
Most substances are liquids or gases at
room temperature.
 Forces between molecules are weak,
allowing molecules to move freely.


Low M.P. & B.P.
Little energy required
to overcome the
(weak)
intermolecular forces
(Usually <200°C)

Melting & Boiling Points
Covalent substance
Melting point (C)
Boiling point (C)
Carbon dioxide
-56
-79
Chlorine
-101
-35
Hydrogen
-259
-253
Methane
-183
-161
Oxygen
-214
-183
Water
0
100
Physical Properties

Volatility
Low B.P. = Volatile
 Evaporate easily (to give a smell)


Electrical conductivity
Do not conduct electricity. (Some exceptions, e.g. graphite)
 No free-moving ions or electrons to conduct electricity


Solubility

Most molecular substances are insoluble in water, but
dissolve in organic solvents. (Some exceptions, e.g. alcohol
and sugar, hydrogen chloride)