Consider the hydrocarbon below.

H H

/ /

C===C

/ /

H H

What is the name of this hydrocarbon?

propene

pentene

butene

ethene

Answer: ethene

Explanation:

The representation of the hydrocarbon is:

H H

/ /

C = C

/ /

H H

So, the double C bond means it is an alkene.

The number of carbon atoms in the molecule is named with the proper prefix:

propa - is used for 3 carbon atoms

penta - is used for 5 carbon atoms

but - is used for 4 carbon atoms

etha - is use for 2 carbon atoms.

Therefore that alkene is name ethene

It is an Alkene because it has a double bond, so it’ll have "ene" at the end. The simplest Alkene has 2 carbons.

2 carbons = "eth"

Look at that! Two carbons! It must be "ethene"