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Hydrocarbons are compounds containing only carbon atoms and hydrogen atoms.

They are represented by the general molecular formula C xHy.

There are different types of hydrocarbons:

CH4 Methane Alkane

C2H4 Ethene Alkene

C6H6 Benzene Arene

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Alkanes are saturated hydrocarbons.

Saturated means they contain the maximum number of hydrogen atoms possible.

They have single bonds and no double bonds.

The general molecular formula of alkanes is CnH2n+2.

The table below shows the names and formulae of some simple alkanes:

N Molecular Formula Name
1 CH4…

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Structure of Alkanes
This is the full structural formula of heptane.

It shows all the atoms and all the bonds in the molecule.

The line represents a covalent bond, formed by sharing a pair of electrons, one from each

Its shortened structural formula is:

CH3 ­ CH2 ­ CH2…

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Branched Alkanes
Alkanes may have straight or branched chains.

It is often possible to draw more than one structural formula for a given molecular formula,

There is often a straight-chain compound and one or more branched-chain compounds with
the same molecular formula.

For C4H10, there are two possible structural formulae:…

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Alkane molecules with cyclic structures are called cycloalkanes.

They have the general formula CnH2n.

They have two fewer hydrogen atoms than the corresponding alkane, because there are no
­CH3 groups at the ends of the chain.

This table shows different ways of representing cycloalkanes.

The skeletal formula shows only…

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Shapes of Alkanes
The best way to show a molecular structure on paper is to use the following:

Represents a bond in the
plan of the paper

Represents a bond in a
direction behind the
plane of the paper

Represents a bond in a
direction in front of the

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What are Alkanes Like?

Whether an alkane is a solid, liquid or gas at room temperature depends on the size of its

The first four members of the series are colourless gases.

Higher members are colourless liquids and the remainder are white waxy solids.

At room temperature and pressure:…

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Chemical Reactions of Alkanes
Alkanes are very unreactive towards many laboratory reagents.

They are unaffected by polar reagents such as acids and alkalis, or oxidising agents such as
potassium manganate.

When they do react, it is usually in the gas phase and energy must be supplied to get the

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Alkenes have the general formula CnH2n.

They are made out of carbon and hydrogen so they are hydrocarbons.

They have at least one double covalent bond.

They are unsaturated because they can make more bonds with extra atoms in addition

Name Formula Skeletal Formula
Propene CH3-CH=CH2

But-1-ene CH3-CH2-CH=CH2…

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Cycloalkenes have 2 less hydrogen atoms than an open-chain alkene.

Properties of Alkenes
The boiling points of alkenes increase as the number of carbon atoms increases.

Ethene, propene and the butenes are gases.

After this, they are liquids and eventually solids.

Shapes of Alkenes
Ethene is a flat molecule…


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