Topic 2: Elements, Compounds and Mixtures - Subtopic 3: Properties of Materials

• Allotrope of carbon • One carbon atom bonds with four other carbons, forming a tetrahedron • Covalent bonds are identical and strong • No intermolecular forces

• Doesn’t conduct electricity • High melting point • Extremely hard

• Useful for purposes where extremely tough material is required • Jewellery • Coating blades in cutting tools

• Allotrope of carbon • One carbon atom bonds with three others forming layers of hexagons, leaving one free electron per carbon atom • Free electrons are free to move, carry charge and migrate along layers, hence can conduct electricity • Covalent bonds are strong, but layers have weak intermolecular forces so layers can slide over other making graphite soft and slippery

• Conducts electricity and heat • High melting point • Soft and slippery

• Pencils • Industrial Lubricant (engines and locks) • Inert electrodes for electrolysis

• Single layer of graphite • Sheet of carbon atoms covalently bonded forming a continuous hexagonal layer • 2D Molecule • Useful in fabricating composite materials and in electronics

• Strong and light (Strong covalent bonds) • Conducts heat and electricity (Free electrons move along surface) • Transparent (Absorbs 2.3% of light) • Flexible (Strong covalent bonds between atoms are flexible)

• Group of carbon allotropes which consist of molecules that form hollow tubes or spheres • Trap other molecules by forming around target molecule • Useful for drug delivery systems • Huge SA, useful catalyst • Excellent lubricants

• Graphene rolled into cylinder • High tensile strength • Conduct electricity

The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles.

The stronger the forces of attraction, the more energy that is needed to overcome them for a state change to occur.

The stronger the forces between the particles the higher the melting point and boiling point of the substance.

Simple molecules have weak intermolecular forces that need little energy to break resulting in low melting and boiling points.

Giant ionic lattices and macromolecular structures have very strong bonds which need lots of energy to break, resulting in high melting and boiling points.

Melting is when a solid (s) changes into a liquid (l).

The process requires heat energy which transforms into kinetic energy, allowing the particles to move.

It occurs at a specific temperature known as the melting point which is unique to each pure solid.

Boiling is when a liquid (l) changes into a gas (g).

This requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and from within the liquid.

It occurs at a specific temperature known as the boiling point which is unique to each pure liquid.

Freezing is when a liquid (l) changes into a solid (s).

This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same.

Water for example freezes and melts at 0 ºC.