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Lesson: Chapter 14 — Hydrocarbons and their derivatives

14.2. Alkenes and the derivatives of ethene 2 of 2

Chloroethene and tetrafluoroethene

Replace hydrogen atoms in ethene with other atoms and you get the derivatives of ethene.

Chloroethene

The compound formed when one hydrogen atom of ethene is replaced by a chlorine atom is called chloroethene. Its formula is C2H3Cl.

The structure of chloroethene: ethene with one hydrogen atom replaced by a chlorine atom.

Tetrafluoroethene

The compound formed when the four hydrogen atoms of ethene are replaced by four fluorine (F) atoms is called tetrafluoroethene. Its formula is C2F4.

The structure of tetrafluoroethene: ethene with all four hydrogen atoms replaced by fluorine atoms.

Ethene and the derivatives of ethene are used to make the polymers we use every day, such as polythene, styrofoam and Teflon.

Why the names say what was changed

Both names are built on ethene, and the front tells you what was swapped in. Chloro means one chlorine; tetra means four and fluoro means fluorine, so tetrafluoroethene has four fluorines. The double bond is untouched in both, so both are still able to open up and link into chains, just as ethene can — the reason they matter. Chloroethene is the monomer of PVC and tetrafluoroethene the monomer of Teflon. Chloroethene is also called vinyl chloride, which is where the name polyvinyl chloride, PVC, comes from.

A derivative is not a hydrocarbon

Chloroethene contains chlorine and tetrafluoroethene contains fluorine, so neither is a hydrocarbon. They are derivatives of the hydrocarbon ethene.

Swap hydrogens, keep the double bond

Chloroethene C2H3Cl has one H replaced by Cl; tetrafluoroethene C2F4 has all four replaced by F.