1) Alkanes have low melting and boiling points

- Made up of covalent molecules held by weak intermolecular forces, so less energy is required to overcome the forces to separate the molecules

- First 4 members are gases at r.t.p.

- Alkanes with 5 to 16 carbon atoms per molecule are liquids and those with more than 17 carbon atoms exist as solids

- Physical properties of alkanes change gradually as molecular size increases

- Alkanes become more viscous because long carbon chains are much more likely to get tangled up and makes it more difficult for the liquid to flow.

2) All members are insoluble in water but soluble in organic solvent

- Like dissolve like

3) Similar for all alkanes

- Alkanes contain the same single C-H and C-C covalent bond

4) Not very reactive

- Strong C-C and C-H bonds require a lot of energy to break.

Reactions of Alkane

§ Combustion

- Smaller alkanes burn easily in air when ignited

- If the combustion is complete, products formed are CO₂ and HHasdasdaosijdoijasH₂O

ð CH₄(g) + 2CO₂(g) à CO₂(g) + 2H₂O(g)

- Reaction is highly exothermic

ð Main use of alkanes as fuels for cooking; fuels for vehicles

- If the combustion is not complete, products formed are CO, C(soot) and H₂O

§ Substitution reaction

- Characteristic reaction of saturated compounds

- Usually slow

- Takes place with chlorine or bromine

- Reaction is catalysed by ultra-violet light

ð Provides the energy to break the covalent bond between the molecules

- Reaction is difficult to control. A mixture of products is usually obtained

Substitution reaction is a reaction in which the hydrogen atoms of an organic molecule are replaced by atoms of other elements.

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