Organic chemistry 1 - Chemistry - page 218

14 Organic chemistry 1

Alkanes
Naming the alkanes
Structural isomerism
The chemical behaviour of alkanes
The ozone hole problem
Methane - another greenhouse gas!
Other uses of alkanes

The chemical behaviour of alkenes
Addition reactions
A special addition reaction of alkene molecules
Other addition polymers
Thermosoftening and thermosetting plastics
Disposal of plastics

Checklist
Additional questions

Alkenes
Naming the alkenes
Where do we get alkenes from?

A lot of the compounds that are present in
living things have been found to be compounds
containing carbon (Figure 14.1). These are known
as organic compounds . All living things are made
from organic compounds based on chains of carbon
atoms which are not only covalently bonded to
each other but also covalently bonded to hydrogen,
oxygen and/or other elements. The organic
compounds are many and varied. Some scientists
suggest that there are more than ten million known
organic compounds.

● Alkanes
Most of the hydrocarbons in crude oil belong to the
family of compounds called alkanes . The molecules
within the alkane family contain carbon atoms
covalently bonded to four other atoms by single
bonds (Figure 14.2). Because these molecules possess
only single bonds they are said to be saturated , as
no further atoms can be added. This can be seen in
the bonding scheme for methane (Figure 14.3). The
physical properties of the first six members of the
alkane family are shown in Table 14.1.
You will notice from Figure 14.2 and Table 14.1
that the compounds have a similar structure and
similar name endings. They also behave chemically in
a similar way. A family with these factors in common
is called a homologous series .

All the members of a homologous series can also be
represented by a general formula. In the case of the
alkanes the general formula is:
C n H 2 n +2
where n is the number of carbon atoms present.
As you go up a homologous series, in order of
increasing number of carbon atoms, the physical
properties of the compounds gradually change.
For example, the melting and boiling points of the
alkanes shown in Table 14.1 gradually increase. This
is due to an increase in the intermolecular forces
(van der Waals' forces) as the size and mass of the
molecule increases (Chapter 3, p. 49).
Under normal conditions molecules with up to
four carbon atoms are gases, those with between five
and 16 carbon atoms are liquids, while those with
more than 16 carbon atoms are solids.

Figure 14.1 Living things contain organic compounds.

You saw in Chapter 6 that crude oil is made up of
a complex mixture of hydrocarbon compounds.
This mixture is a very important raw material in the
organic chemical industry. Our world would be a
very different place without these substances. Can
you imagine life without the substances from oil
and natural gas? There would be no oil-based fuels,
such as petrol and diesel, and the chemical industry,
particularly the plastics industry, would also suffer
since substances extracted from oil are used as raw
materials for many plastics.