Bulk Properties

Section 1 of 7What are bulk properties?

Properties of large collections

• Properties of large collections Bulk properties include melting and boiling points, electrical and thermal conductivity, hardness and flexibility.
• A single atom has none of these properties.
  • They appear only when very large numbers of particles act together.

Where they come from

• Where they come from They are controlled by the type of bonding (ionic, covalent, metallic) and by how strong the forces are between particles.
• The arrangement of the particles, for example in layers or a giant lattice, matters just as much.

Section 2 of 7Brittle or malleable

Response to a force

Metals are malleable

• Metals are malleable Metal atoms sit in regular layers that can slide over each other when a force is applied.
• The sea of delocalised electrons keeps the structure bonded, so the metal changes shape without cracking.

Ionic solids are brittle

• Ionic solids are brittle A force shifts a layer of ions so that ions of the same charge line up and repel, and the crystal shatters.

Giant covalent solids are brittle

• Giant covalent solids are brittle Applying a large force breaks the rigid network of covalent bonds, so the material snaps rather than bends.

Section 3 of 7Carbon allotropes compared

Form of carbon	Structure	Bulk properties
Diamond	Each atom bonded to four others	Extremely hard, very high melting point, does not conduct
Graphite	Layers with weak forces between them	Soft and slippery, conducts electricity, very high melting point
Fullerenes	Hollow cages or tubes of carbon atoms	Conduct electricity, slippery or useful as cages for other molecules
Carbon nanotubes	Rolled-up sheets of hexagons	High tensile strength, good conductors of heat and electricity
Graphene	Single layer of hexagons	Extremely strong, conducts heat and electricity, almost transparent

Section 4 of 7Polymers

1

Most polymers are solid at room temperature because their molecules are very long.

2

Atoms inside each polymer chain are held by strong covalent bonds.

3

Between separate chains there are intermolecular forces. Because the chains are long, these forces add up and are stronger than those between small simple molecules.

4

Those forces are still much weaker than ionic or covalent bonds, so polymers melt at lower temperatures than giant ionic or covalent substances.

Section 5 of 7Nanoparticles change properties

Silver as an example

• Silver as an example Bulk silver is a shiny, malleable metal that does not corrode and is mainly used in jewellery.
• Silver nanoparticles are only 1 to 100 nm across and have a very large surface area to volume ratio.

New uses

• New uses In this form silver kills bacteria, so it is used in deodorants, fridge linings and socks to reduce odours.

The lesson

• The lesson The same substance can behave differently as a bulk solid and as nanoparticles, because the surface area to volume ratio changes.

Section 6 of 7Key terms

Term	Meaning
Bulk property	A property of a material that arises from many particles acting together, not from one atom.
Malleable	Able to be bent or hammered into shape without breaking.
Brittle	Likely to crack or shatter when a force is applied.
Intermolecular force	A force of attraction between separate molecules.
Nanoparticle	A particle between 1 and 100 nanometres across.

Section 7 of 7Exam technique

1

Saying an individual atom is hard or has a melting point. These are properties of the bulk material only.

2

Thinking only covalent substances have giant structures. Ionic compounds and metals do too.

3

Writing that polymers have weak bonds. The covalent bonds in the chains are strong; the weak forces are between chains.

4

Forgetting that nanoparticle properties are explained by the large surface area to volume ratio.