Section 7 - Alkenes

Question 1

How are alkenes different to alkanes?

Answer 1

The difference is in the presence of a carbon-carbon double covalent bond (C=C) somewhere in the carbon chain.

Question 2

In alkenes, not all possible single bonds have been made. What does this mean?

Answer 2

These molecules are unsaturated

Question 3

What are the first three alkene molecules?

Answer 3

Ethene, propene, butene,

Question 4

What are isomers?

Answer 4

Molecules with the same molecular formula but different structures

Question 5

In alkenes, why is the C=C bond called a ‘rigid’ bond?

Answer 5

The C=C bond does not allow the same free rotation and flexibility around itself as a C-C bond.

Question 6

In alkenes, although there is a rigid C=C bond, the rest of the carbon chain is the same as in an alkane molecule. What does this mean?

Answer 6

Rotation is allowed around the single bonds

Question 7

The presence of the C=C bond dictates the chemical properties of alkenes. What are these properties? (3)

Answer 7

1) They are reactive compounds, undergoing many different types of chemical reactions.
2) They are used extensively to form polymers, e.g. poly(ethene).
3) They do not burn clearly, giving very yellow flames and lots of soot.

Question 8

How can you test whether a compound is an alkene?

Answer 8

By adding it to bromine water. Alkenes decolourise bromine water, turning it from orange to colourless.