Ionic, Covalent, Giant Molecular Structures

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IGCSE1
Between metals and non-metals.
Electrons are transferred from the metal
atoms to the non-metal atoms.
The atoms get full outer energy levels and
become more stable.

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Sodium +chlorine sodium chloride
The sodium ion has obtained an electron
configuration like neon.
The chlorine atom has an electron configuration like
argon.

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The oppositely charged ions attract each
other and are pulled or bonded together by
strong electrostatic forces.
This bonding is called ionic or electrovalent
bonding.
1. Draw diagrams to represent the bonding in
each of the following ionic compounds.
a) Magnesium fluoride ሺ‫ܨ݃ܯ‬ଶሻ
b) Potassium fluoride ‫ܨܭ‬
c) Lithium chloride ‫݈ܥ݅ܮ‬
d) Calcium oxide ‫ܱܽܥ‬ሻ

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The ions are packed together in a regular
arrangement called a lattice.
Here oppositely charged ions attract one
another strongly.
Ionic structures are:
1. Solids at room temperature
2. High melting and boiling points (due to strong
intermolecular forces).
3. Usually hard substances.
4. Cannot conduct electricity when solid, because ions are
not free to move.
5. Mainly dissolve in water (water is able to bond with both
negative and positive ions which breaks up the lattice).
6. Usually conduct electricity when molten or in an
aqueous solution (ions are free to move).

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When ionic compounds combine their
respective charges need to balance.
e.g. how many‫݈ܥ‬ି
ions will need to bond with
an ‫݃ܯ‬ଶା
ion to balance?
So the formula will be ‫݈ܥ݃ܯ‬ଶ
Using the table write the
formula for:
a) Copper (I) oxide
b) Zinc phosphate
c) Iron (III) chloride
d) Lead bromide

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Between non-metal atoms
Sharing of electrons
Each atom wants a noble gas electron
configuration i.e. 8 electrons in its outer shell.
It gets these by sharing electrons with other
atoms.
Between non-metal atoms
Sharing of electrons
e.g. ‫ܪ‬ଶ
This shared pair of electrons is
called a single covalent bond.

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Other covalent compounds include:
1. Methane (࡯ࡴ૝)
Methane is tetrahedral
2. Ammonia (‫ࡴۼ‬૝)
Ammonia is pyramidal

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2. Water (ࡴ૛ࡻ)
Water has a bent orV-shape
2. Carbon dioxide (࡯ࡻ૛)
Carbon dioxide is linear in shape.
ܱ ൌ ‫ܥ‬ ൌ ܱ

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1. Draw diagrams to represent the bonding in
each of the following covalent compounds.
a) Tetrachloromethane ‫݈ܥܥ‬ସ
b) Oxygen gas ܱଶ
c) Hydrogen sulphide ‫ܪ‬ଶܵ
d) Hydrogen chloride ‫݈ܥܪ‬
e) Ethene ‫ܥ‬ଶ‫ܪ‬ସ
f) Methanol ‫ܪܥ‬ଷܱ‫ܪ‬
g) Nitrogen ܰଶ
2. Why is the water molecule bent?
Covalent compounds can either be simple molecular or
giant molecular.
Simple Molecular compounds
Formed from only a few atoms.
Strong covalent bonds between atoms in a molecule
(intramolecular bonds).
Weak bonds between the molecules (intermolecular
bonds).
These weak bonds can be Van der Waals bonds.These
increase in strength as the molecule gets bigger.

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Giant Molecular compounds
Formed from hundreds of thousands of atoms.
Examples are diamond, graphite and silicon (IV)
oxide and plastics such as polythene.
Simple structures
They are usually gases, liquids or solids with low melting and
boiling points.
MP are low due to the weak intermolecular forces of attraction.
Giant structures
High melting points as structure is held together by strong
covalent bonds.
Generally do not conduct electricity when molten or dissolved in
water.*
*Some molecules react with water to form ions (e.g. HCl) which
can then conduct electricity.
Generally do not dissolve in water.

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When an element can exist in more than one
physical form in the same state is said to
exhibit allotropy or polymorphism.
Each physical form is called an allotrope.
E.g. sulphur, tin, carbon and iron.
The allotropes of carbon are diamond and
graphite.

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Graphite is a form of carbon in which the carbon
atoms form layers.These layers can slide over
each other, so graphite is much softer than
diamond.
It is used in pencils, and as a lubricant. Each
carbon atom in a layer is joined to only three
other carbon atoms.
Graphite conducts electricity.

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Diamond is a form of carbon in which each
carbon atom is joined to four other carbon
atoms, forming a giant covalent structure.
As a result, diamond is very hard and has a
high melting point.
It does not conduct electricity.

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Graphite can conduct electricity due to the vast
electron delocalization within the carbon layers.
These valence electrons are free to move, so are
able to conduct electricity. However, the electricity
is only conducted within the plane of the layers.
Diamond is a carbon tetrahedral shape and so
carbons are linked with each other and are not free
to move in plates like graphites can.That is also
why graphite is a lubricant and diamond is a
cutting abrasive.
Silica, which is found in sand, has a similar
structure to diamond.
It is also hard and has a high melting point,
but contains silicon and oxygen atoms,
instead of carbon atoms.
The fact that it is a semi-conductor makes it
immensely useful in the electronics industry:
most transistors are made of silica.

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Buckminsterfullerene is yet another allotrope
of carbon.
It is actually not a giant covalent structure,
but a giant molecule in which the carbon
atoms form pentagons and hexagons - in a
similar way to a leather football.
It is used in lubricants.
Uses of diamond and graphite.

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Soda Glass
Found in bottles and windows
It is made by heating a mixture of sand
(silicon (IV) oxide), soda (sodium
carbonate) and lime (calcium oxide).
Borosilicate Glass
Pyrex is borosilicate glass
boron oxide + silicon (IV) oxide
stronger than soda glass
used in cooking utensils and laboratory
glass ware.

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Form a giant structure
Atoms packed closely together in
a regular arrangement
valence electrons tend to move
away from their atoms
These form a “sea” of delocalised
electrons which surround a lattice
of positively charged metal ions.
Positively charged ions held
together by the strong
attraction to the mobile
electrons.
The electrostatic force between
the electrons and the metal ions
acts in all directions.

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1. High melting and boiling points – due to the strong
forced of attraction between the metal ions and
electrons.
2. Good conductors of electricity – delocalised electrons
are free to move.
3. Good conductors of heat – atoms are closely packed
and can pass “vibrations” on to the next atom.
4. Malleable (can be bent) and ductile (can be drawn
into a wire) – the positive ions are arranged in layers
which can slide past eachother when a force is applied.
Why does electrical conductivity of
metals decrease with an increase in
temperature?

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Complete the worksheet handed out to you.
Spare copies can be found on Moodle.