(4.23-4.28) Alkenes

What is an alkene?

unsaturated hydrcarbons

What does ‘unsaturated’ mean?

the carbon atoms do not only have single bonds

What is the functional group of alkenes?

C=C

What is the general formula of alkenes?

C_nH_2n

What does it mean when a compound is called, for example, but-1-ene?

The double bond is on the ‘first’ carbon, which can be counted from L→R or R→L

Describe and explain the reactivity of alkenes.

Alkenes are more reactive than alkanes as:

• they have a double bond

• which can ‘open up’ and allow for more single bonds to be formed

• so they are more reactive

What kind of reactions occurs between alkenes and bromine?

Addition reactions

Describe the reaction between alkenes and bromine.

As with any halogen and alkene,

the double bond opens up

and each bromine atom binds to a carbon atom

forming a dibromoalkane

What is the bromine water test used for?

To test whether a substance is an alkane or an alkene

Describe the bromine water test.

Bromine water is an orange solution

When an alkane is added, no reaction occurs so it remains an orange solution.

When an alkene is added, the bromine binds to the carbons

there are no free bromine

so it decolourises.