Ionic, Covalent
and Metallic
Structures
PURE substances have different STRUCTURES
depending on the type of BONDING they have
IONIC
COVALENT
METALLIC
eg copper
eg sodium
chloride (salt)
SIMPLE
eg carbon dioxide,
water
GIANT eg
diamond,
graphite
The structure of a substance decides what its
PHYSICAL PROPERTIES will be.
IONIC
Ionic substances are compounds of metals and non-metals (eg
sodium chloride, copper oxide, magnesium sulphide etc)
They are made of IONS: atoms which have lost or gained electrons
giving them a positive or negative CHARGE
Positive
sodium ion
Na+
Negative
chloride ion
Cl-
The + ions and – ions STRONGLY ATTRACT each other to
make a regular crystal structure
Because of the very STRONG BONDS between the IONS,
ionic compounds have HIGH MELTING & BOILING POINTS
Strong ionic
bond
Sodium chloride
melts at over 800°C
Ionic
compound
Melting
point (°C)
Iron chloride
677
Potassium chloride
770
Sodium chloride
801
Copper oxide
1446
Calcium oxide
2707
As ionic compounds are made of CHARGED IONS, they can
CONDUCT ELECTRICITY but ONLY if the ions can MOVE.
If it is MOLTEN
the ions can
move
MELT
+
- + - +
- + - + - + - +
+
800°C
If it is DISSOLVED
the ions can move
- +
+ - +
+ -
+
-
DISSOLVE
+
-
+ - +
+
+ -
-
-
+
20°C
H2O
+
MOLTEN IONIC
COMPOUND
-
+ -
-
+
+
+
-
-
+
+
+
-
MOLTEN ionic compounds CONDUCT ELECTRICITY
When salt is put in water, H2O molecules pull the ions apart to
make a solution. This lets the ions move around.
H20
molecule
Ions free
to move
around
PURE WATER
SOLID SALT
SALT SOLUTION
DISSOLVED ionic compounds also CONDUCT ELECTRICITY
Ionic Bonding Questions
1.List two compounds that contain ionic
bonds. (Grade D)
2.Describe three properties of ionic
compounds. (Grade C)
3.Explain why ionic compounds often
form giant structures – maybe draw a
diagram (Grade B)
SIMPLE MOLECULAR SUBSTANCES
These are substances like carbon dioxide CO2, water H2O and
methane CH4 which are always made of simple molecules
whether they are SOLIDS, LIQUIDS OR GASES
H atom
O atom
Whole thing
= H2O molecule
MOLECULES ONLY WEAKLY ATTRACT EACH OTHER
VERY STRONG bonds
BETWEEN ATOMS
(so molecule is very hard to
break up)
WEAK bonds BETWEEN
MOLECULES
(so molecules are easy to
separate)
This means simple molecular substances have LOW melting
and boiling points
Compound
Mpt
(°C)
Bpt
(°C)
State at
room temp
Water H2O
0
100
Liquid
Butane C4H10
-138
-0.5
Gas
Methane CH4
-182
-164
Gas
Carbon dioxide CO2
-
-78
Gas
Oxygen O2
-218
-183
Gas
Hydrogen H2
-259
-252
Gas
Solid oxygen
at -240°C
Liquid oxygen
boiling at -183°C
As the bonds between the molecules are weak, simple
molecular substances are weak and soft when solid.
As the molecules are NOT CHARGED simple molecular
substances DON’T CONDUCT ELECTRICITY when solids,
liquids or gases.
GIANT MOLECULAR SUBSTANCES
In these materials strong covalent bonds join atoms together
with other atoms of the same type to make giant structures,
rather than little groups.
DIAMOND
Carbon
atom
Only
STRONG
bonds
Every C
atom joined
to 4 others
(this is only part of
the structure - the
same pattern carries
on in every direction)
SILICA (Silicon dioxide SiO2) has a similar structure to diamond
Every Si
atom joined
to 4 O atoms
Silica is the main substance in ROCKS. Pure silica is called
QUARTZ
Because all the atoms in Giant Structures are joined by
STRONG BONDS they:
• Have HIGH melting / boiling points
• Are usually HARD and STRONG
Because all the atoms in Giant Structures are UNCHARGED,
they will not conduct electricity.
GRAPHITE – a special case
Common form of carbon found in soot, charcoal, pencil leads etc
Carbon atoms each joined
to 3 others with STRONG
bonds to make hexagonal
sheets of atoms
WEAK
BONDS
STRONG
BONDS
The sheets of atoms are
joined to other sheets by
WEAK bonds
As the bonds
between the
layers of atoms
are weak, they
can easily slide
over each other
As the C atoms are only bonded to
3 others, the extra electrons form
clouds of ‘free electrons’ between
the layers
GRAPHITE - Properties
The STRONG BONDS between the
ATOMS mean it has HIGH
MELTING and BOILING POINTS
The WEAK BONDS between the
LAYERS mean it is SOFT and
SLIPPERY as the layers SLIDE over
each other easily (used in pencils and
as a solid lubricant)
The FREE ELECTRONS between the layers mean that
graphite CONDUCTS ELECTRICITY (used as sliding contacts
in electric motors)
Covalent Bonding Questions
1.List one covalent compound that has
a simple structure and one that has a
giant structure. (Grade C)
2.Describe two properties of simple
covalent compounds and two
properties of giant covalent
compounds. (Grade B)
3.Explain why graphite and diamond
have different properties (Grade A)
METALS
In a metal the atoms are held together by strong bonds in
regular structures.
This means most metals have high melting and boiling points
and are hard and strong
In a metal the atoms LOSE SEVERAL OF THEIR OUTER
ELECTRONS which drift around between the metal ions as
FREE ELECTRONS.
As they have LOST a
few electrons, the
atoms become
POSITIVE IONS
Free (“delocalised”)
electrons
The large number of free electrons makes all metals are
GOOD CONDUCTORS of electricity AND heat.
The regular structure means
the layers of atoms can fairly
easily slide over each other
without breaking the bonds
(though not as easily as
graphite) and so metals are
MALLEABLE (bend rather
than snap)
Metallic Bonding Questions
1.List two elements that contain
metallic bonding. (Grade D)
2.Describe three properties elements
that contain metallic bonding. (Grade
C)
3.Explain why metallic structures
conduct electricity OR are malleable
(Grade B)
SUMMARY - Descriptions
IONS
ONLY
IONIC
Crystals
Dissolve in water
eg sodium chloride (salt)
SIMPLE Covalent
Usually Gases
eg CO2, H2O
MOLECULES
ONLY
METALLIC
Strong malleable solids
IONS +
Don’t dissolve
FREE
eg copper
ELECTRONS
ATOMS
joined into
GIANT
MOLECULE
S
GIANT Covalent
Hard strong solids
Don’t dissolve
eg diamond
(graphite – special case)
SUMMARY - PROPERTIES
Structure Property
Reason
Ionic
HIGH mpt/bpt
CONDUCT: Solid NO
Molten YES Dissolved YES
Strong bonds between IONS
Ions can’t move
Ions can move to carry current
Covalent – LOW mpt/ bpt (often gas at
room temp). Soft when solid
Simple
molecular
CONDUCT: Never
Bonds between MOLECULES
very weak.
Molecules aren’t charged
Covalent – HIGH mpt/bpt. Hard & strong Strong bonds between all ATOMS
giant
No free charges/electrons
molecular
CONDUCT: Never
Covalent graphite
HIGH mpt/bpt
Soft & slippery
CONDUCT: YES (fairly well)
Strong bonds between ATOMS
Weak bonds between LAYERS
Free electrons between layers
Metallic
HIGH mpt/bpt. Hard & strong Strong bonds between IONS
Malleable
Regular structure, layers slide
CONDUCT: YES (very well) Free electrons between ions