Bulk properties

Individual atoms do not have the physical properties of the substances that contain them. For example, a copper atom cannot conduct electricity, even though a piece of copper can do this. Bulk properties are properties due to many atoms, ions or molecules acting together.

Melting and boiling points

Chemical bonds are broken or overcome during melting and boiling. The stronger these bonds are, the higher the melting point and boiling point.

Type of substanceExample(s)Bonds brokenRelative bond strength
Simple molecularOxygen, waterIntermolecular forcesWeak
Ionic substanceSodium chlorideIonic bondsStrong
Giant covalentSilicon oxide, diamondCovalent bondsStrong
MetalMagnesium, sodiumMetallic bondsStrong

Simple molecular substances:

  • have relatively low melting and boiling points
  • are usually gases or liquids at room temperature, or solids that are easily melted

Ionic substances, giant covalent substances and metals:

  • have relatively high melting and boiling points
  • are usually solids at room temperature

Malleable or brittle

Malleable substances can be bent or hammered into shape without shattering. Metals are malleable. When a force is applied, layers of metal ions can slide over each other while still being attracted to the ‘sea’ of delocalised electrons.

Malleable metalLayers of atoms slide over each other when metals are bent or stretched

Ionic substances and giant covalent substances are usually brittle. They shatter when bent or hit because many strong ionic bonds or covalent bonds break at once.

Conducting electricity

A substance can conduct electricity if both:

Type of substanceConducts electricity? Reason
Simple moleculeNoSimple molecules are not charged
Ionic compoundOnly when molten or dissolvedIons are charged particles, free to move about when the substance is molten or dissolved (not when it is solid)
Giant covalentNoThe individual atoms are not charged
MetalYesContains delocalised electrons, free to move about

Note that graphite, graphene and fullerenes are covalent substances that do conduct electricity. This is because, like metals, they contain delocalised electrons.

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