(d) Alkenes

4:23 know that alkenes contain the functional group >C=C<

Alkenes are a homologous series of hydrocarbons which contain a carbon-carbon double bond. This double bond is shown in formulae as a double line.

The names of alkenes end with “ene”.

An example is ethene, the structural formula for which is CH₂ = CH₂

For a molecule with more than two carbon atoms, the position of the double bond within the molecule can vary as indicated by the name and the structural formula.

4:25 explain why alkenes are classified as unsaturated hydrocarbons

Saturated:   A molecule containing only single bonds between carbon atoms. For example, alkanes as described as saturated molecules.

Unsaturated:   A molecule containing a carbon-carbon double or triple bond. For example, alkenes as described as unsaturated molecules.

4:26 understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers. Knowledge of cis/trans or E/Z notation is not required

The displayed formulae show all the atoms and bonds drawn out.

The molecular formulae just show the number of each type of atom in the molecule.

4:27 describe the reactions of alkenes with bromine, to produce dibromoalkanes

Alkenes react with bromine water. UV light is not required for this reaction.

The double bond is broken and the bromine atoms are added. This is an addition reaction.

During this reaction there is a colour change from orange to colourless.

For example:

This is how we can test for the presence of an alkene or another type of unsaturated molecule.



4:28 describe how bromine water can be used to distinguish between an alkane and an alkene

In the absence of UV light an alkane added to bromine water will not react: the bromine water will stay orange.

However, alkenes react with bromine water even without UV light. There will be a colour change of orange to colourless.




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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals

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