C2.2 How do structures influence

the properties and uses of

substances?

Summary

Substances that have simple molecular, giant ionic

and giant covalent structures have very different

properties.

Ionic, covalent and metallic bonds are strong.

The forces between molecules are weaker, e.g. in

carbon dioxide and iodine.

Nanomaterials have new properties because of their

very small size (about the size of 10 atoms).

You should be able to:

to relate the properties of substances to their uses

to suggest the type of structure of a substance

given its properties

to evaluate developments and applications of new

materials, e.g. Nanomaterials, smart materials.

Substances

Molecular

Giant

Ionic

Covalent

Metallic bonds

Nanomaterials

Structure

Intermolecular

Lattices

Delocalised

Fullerene

Graphite

Alloys

Polymers

Catalysts

Thermosoftening

Thermosetting

Nanoscience

Key words

Molecules

(a) Substances that consist of simple molecules are gases,

liquids or solids that have relatively low melting points and

boiling points.

Molecules

(b) Substances that consist of simple molecules have

only weak forces between the molecules (intermolecular

forces). It is these intermolecular forces that are

overcome, not the covalent bonds, when the substance

melts or boils.

Molecules

(c) Substances that consist of simple molecules do not

conduct electricity because the molecules do not have an

overall electric charge.

Ionic compounds

(a) Ionic compounds have regular structures (giant ionic

lattices) in which there are strong electrostatic forces in

all directions between oppositely charged ions. These

compounds have high melting points and high boiling

points.

Ionic compounds

(b) When melted or dissolved in water, ionic compounds

conduct electricity because the ions are free to move

and carry the current.

Ionic compounds

(b) When melted or dissolved in water, ionic

compounds conduct electricity because the ions are free

to move and carry the current.

Ionic solid Molten ionic

compound

Ionic compound in

solution

Ions are fixed in a

lattice.

They vibrate but cannot

move around – it does

not conduct electricity

High temperature

provides enough energy

to overcome the many

strong attractive forces

between ions. Ions are

free to move around

within the molten

compound – it does

conduct electricity

Water molecules are

separate ions form the

lattice. Ions are free to

move around within the

solution – it does not

conduct electricity

Covalent structures

(a) Atoms that share electrons can also form giant

structures or macromolecules. Diamond and graphite

(forms of carbon) and silicon dioxide (silica) are examples

of giant covalent structures (lattices) of atoms. All the atoms

in these structures are linked to other atoms by strong

covalent bonds and so they have very high melting points.

Covalent structures

(b) In diamond, each carbon atom forms four covalent

bonds with other carbon atoms in a giant covalent structure,

so diamond is very hard.

Covalent structures

(c) In graphite, each carbon atom bonds to three others,

forming layers. The layers are free to slide over each other

and so graphite is soft and slippery.

(d) In graphite, one

electron from each

carbon atom is

delocalised. These

delocalised

electrons allow

graphite to conduct

heat and electricity.

(e) Carbon can also form fullerenes with

different numbers of carbon atoms.

Fullerenes can be used for drug delivery

into the body, in lubricants, as catalysts,

and in nanotubes for reinforcing materials,

eg in tennis rackets.

The nanotube's structure allows it to be used as a container for

transporting a drug in the body. A molecule of the drug can be

placed inside the nanotube cage. This keeps the drug 'wrapped

up' until it reaches the site where it is needed. In this way, a

dose that might be damaging to other parts of the body can be

delivered safely to, for example, a tumour

Metals

(a) Metals conduct heat and electricity because of

the delocalised electrons in their structures.

(b)The layers of atoms in metals are able to slide

over each other and so metals can be bent and

shaped.

Metals

(c) Alloys are usually made

from two or more different

metals. The different sized

atoms of the metals distort the

layers in the structure, making

it more difficult for them to slide

over each other, and so make

alloys harder than pure metals.

(d) Shape memory alloys can return to their original

shape after being deformed.

http://www.youtube.com/watch?v=Y7jjqXh7bB4

When nitinol is cool it can be bent and twisted. When it is

heated it then returns to its original shape.

It can be used in dental braces. As it warms in the mouth

it tries to return to its remembered shape and so can pull

the teeth into shape with it.

What other uses can you think of for nitinol?

What other uses can you think of for nitinol?

When nitinol is cool it can be bent and twisted. When it is

heated it then returns to its original shape.

It can be used in dental braces. As it warms in the mouth

it tries to return to its remembered shape and so can pull

the teeth into shape with it.

Polymers

(a) The properties of polymers depend on what they

are made from and the conditions under which they

are made. For example, low density (LD) and high

density (HD) poly(ethene) are produced using different

catalysts and reaction conditions.

Polymers

(b) Thermosoftening polymers consist of individual,

tangled polymer chains.

Polymers

(b) Thermosetting polymers consist of polymer

chains with cross-links between them so that they do

not melt when they are heated.

Choose from the table the polymer that would be best

suited for making:

1.a disposable cup for hot drinks

2.Clothing

3.a measuring cylinder.

Z

X

Y

Nanoscience(a) Nanoscience refers to structures that are 1-100 nm in

size, of the order of a few hundred atoms.

Nanoscience

Such as:

• new computers,

• new catalysts,

• new coatings,

• highly selective sensors and

• stronger and lighter building materials.

Nanoparticles show different properties to the same

materials in bulk

They have a high surface area to volume ratio, which

may lead to new developments.

Some nanoparticle have some strange properties –

this means we have to be careful that they don’t have

any unknown harmful properties.

Q6. (a) Copper is a metal. Explain how it conducts electricity.

copper has free electrons / electrons that move throughout the structure

1 mark

but

• in copper, electrons from the highest (occupied) energy level /outer

shell, are free / can move throughout the structure

gains 2 marks

Q1. This question is about giant structures. Diamond, graphite and silicon

dioxide all have giant structures.

(a) The diagrams show the structures of these three substances.

Draw a line from each structure to its name.

(b) Complete the sentences using words from the box.

covalent four hard ionic shiny

soft three two

(i) Diamond, graphite and silicon dioxide have high melting points

because all the atoms in their structures are joined by strong

............................................... bonds.

(ii) In diamond each atom is joined to ............................................... other

atoms.

(iii) Diamond can be used to make cutting tools because it has a rigid

structure which makes it very ................................................

(iv) In graphite each atom is joined to ............................................... other atoms.

(v) Graphite can be used to make pencils because it has a structure which

makes it ...............................................

(c) When a diamond is heated to a high temperature and then

placed in pure oxygen it burns. Carbon dioxide is the only

product.

Name the element in diamond.

...................................................................................

Graphene

Scientists have made a new substance called graphene. The bonding and structure of graphene are similar to graphite.

Graphene is made of a single layer of the same atoms as graphite.

Graphene Graphite

(b) Graphite is a non-metal.

Use the information to explain why graphite conducts electricity.

idea that

• in graphite, only three bonds are formed by each carbon atom

for 1 mark

• one outer electron (per atom), free to move

for 1 mark

• an electric current is a flow of (free) electrons

for 1 mark

Q10. The diagram represents the structure of graphite.

Use your knowledge and understanding of the

structure of graphite to explain why graphite can be

used:

(a) in the ‘leads’ of pencils;

(a) made of layers of carbon atoms

weak forces of attraction between layers / weak vertical bonds

candidate refers to the diagram

layers can slide over each other

layers peel off

Q10. The diagram represents the structure of graphite.

Use your knowledge and understanding of the

structure of graphite to explain why graphite can be

used:

(b) as an electrical conductor.

because there are electrons

which are free (to move)

reason for free electrons / each carbon atom has 3 covalent bonds