Heteroatoms and functional groups

The idea

An element that replaces hydrogen in a hydrocarbon chain is a heteroatom; heteroatoms and groups containing them give a compound specific properties regardless of the length and nature of its carbon chain, and are called functional groups.

A replacement

In propane, every valency of carbon is satisfied by carbon and hydrogen atoms. Now one hydrogen atom is taken out and an atom of another element, such as chlorine, takes its place.

Is the valency of carbon still satisfied?

• Yes, the valency of carbon remains satisfied
• No, carbon is left with a free valency
• Carbon now has five valencies

Replace a hydrogen

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Heteroatoms give the properties

The carbon chain can be short or long. What gives the compound its specific properties is the heteroatom or the group that holds it.

An element that replaces hydrogen in a hydrocarbon chain is a heteroatom. Heteroatoms and groups containing them give a compound specific properties regardless of the length and nature of its carbon chain, and are called functional groups.

Notes

An element that replaces hydrogen in a hydrocarbon chain is a heteroatom. Heteroatoms and the groups containing them give specific properties regardless of the carbon chain, and are called functional groups.

Check yourself

What is an element that replaces hydrogen in a hydrocarbon chain called?

What are heteroatoms and the groups containing them called, when they give a compound specific properties?

A chlorine atom replaces one hydrogen atom in a hydrocarbon. What happens to the valency of carbon?

In CH₃CH₂Cl, which atom is the heteroatom?

• A heteroatom — correct. Yes!
• A hydrocarbon. A hydrocarbon is a compound of only carbon and hydrogen. An element that replaces hydrogen is a heteroatom.
• An isomer. Isomers are compounds with the same formula and different structures. An element that replaces hydrogen is a heteroatom.
• Saturated groups. Saturated describes a compound with only single bonds between carbon atoms. These atoms and groups are called functional groups.
• Functional groups — correct. Yes!
• Carbon skeletons. The skeleton is the chain of carbon atoms. The heteroatoms and groups containing them are called functional groups.
• A free valency is left on the carbon. Chlorine bonds in the place of hydrogen, so the valency of carbon remains satisfied.
• Carbon gets a fifth bond. Carbon keeps four bonds. Chlorine takes the place of hydrogen.
• It remains satisfied — correct. Yes!
• Chlorine — correct. Yes!
• Hydrogen. Hydrogen is the atom that is replaced. The atom that replaces it is the heteroatom.
• Carbon. Carbon makes the chain. The atom that replaces a hydrogen is the heteroatom, here chlorine.