Properties of Giant covalent molecules (macromolecules)
Some substances that are covalently bonded form giant molecules (macro molecules)
Examples you need to know about are: sand (silica – silicon dioxide), diamond and graphite.
Silica – silicon dioxide
Made from silicon and oxygen atoms held together by strong covalent
bonds.
Basic formula SiO2.
Properties : High melting point, Does not conduct electricity
You should be able to label the silicon and oxygen atoms
You should be able to identify this picture as silica and describe its
structure,
You should know the properties of silica
Diamond - carbon
Made from carbon atoms held together by strong covalent bonds
In diamond each carbon atom forms 4 covalent bonds
Properties : very hard, very high melting point, does not conduct
electricity
You should know what type of atoms diamond is made from
You should be able to identify this picture as diamond
You should know the properties of diamond
Graphite - carbon
Made from carbon atoms held together by strong covalent bonds
In graphite each carbon atom forms 3 covalent bonds
Properties : very soft and slippery, very high melting point, good
conductor of electricity
You should know what type of atoms graphite is made from
You should be able to identify this picture as graphite
You should know the properties of graphite
Higher Tier – as well as the other stuff you should be able to do this……...
Silica – silicon dioxide
Has a high melting point because…..
all the atoms are linked to all the other atoms by strong
covalent bonds. It takes a lot of energy to break these bonds
and melt silica.
Diamond - carbon
Has a high melting point because…..
The carbon atoms are linked by 4 strong covalent bonds. It
takes a lot of energy to break these bonds to melt diamond.
Is hard because…….
There are 4 very strong covalent bonds holding each atom of
carbon to the others so they do not break off without a large
force
Graphite - carbon
Does not conduct electricity because…….
There are no free electrons to carry the current
Has a high melting point because…..
The carbon atoms are linked by 3 strong covalent bonds. It
takes a lot of energy to break these bonds to melt graphite.
Is soft and slippery because…….
The 3 very strong covalent bonds hold the atoms of
carbon in a layered structure. The 4th electron is delocalised
(free to move) between the layers of carbon atoms and allows
the layers to slide over each other very easily.
Is a very good conductor of heat and electricity because…….
The 4th electron from each carbon atom is delocalised (free to
move) between the layers of carbon atoms and it flows to carry
a current or moves around (diffuses) to transfer heat energy.
You should be able to explain why silica, diamond and graphite have high melting points.
You should be able to describe the structure of diamond
You should be able to explain why diamond is very hard
You should be able to describe the structure of graphite
You should be able to explain why graphite is very soft
You should be able to explain why graphite is a good conductor of electricity