science

1. Alkanes
Alkanes are hydrocarbons because they are compounds of carbon
and hydrogen only. Their general formula is CnH2n+2. Inside the
molecules, the bonds are strong covalent ones. The forces of
attraction between the alkane molecules are weak so small
alkanes (1 to 4 carbon atoms) are gases. The forces of attraction
increase with the size of the alkane molecules and those with 17
or more carbon atoms are solids.
Name Molecular
formula
Structural formula m.p.
o
C
b.p.
o
C
State
at
20o
C
Methane CH4

increases

increases

increases


increasesincreases

increases

gas
Ethane C2H6
gas
Propane C3H8
gas
Butane C4H10
C CCC
HH
H
HH
H
H
H
H
H
gas

2. The alkanes are very unreactive when added to common chemicals
such as acids and alkalis. This is because the C-C and C-H bonds
are unreactive with chemicals in solution.
Alkanes do burn so they are used as fuels. Petrol has C8H18
molecules in it and wax is made up of C20H42 molecules. Methane
(CH4) is the gas you have for cooking and heating at home. When
the alkanes burn in a good supply of air, carbon dioxide and water
are the products.
CH4 + 2O2  CO2 + 2H2O
C3H8 + 5O2  3CO2 + 4H2O
The C-H bond is
unreactive towards
chemicals in solution
The C-C bond is
unreactive towards
chemicals in solution