STUDENT SPACE · TOPIC 1

Formulae and organic families

Recognise organic families and draw compounds with correct carbon valency.

The essentials

C₂H₆O counts atoms. CH₃CH₂OH shows their arrangement. A displayed formula shows every atom and bond.
Alkanes have C–C single bonds. Alkenes contain C=C. Alcohols contain –OH. Carboxylic acids contain –COOH.
Alkanes: CₙH₂ₙ₊₂. Alkenes with one C=C: CₙH₂ₙ. Alcohols: CₙH₂ₙ₊₁OH.
Members share a functional group and general formula. Consecutive members differ by CH₂.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

How do neighbouring members of a homologous series differ?

Need a hint for Question 1?

Count atoms before judging whether two formulae describe the same molecule.

Check Question 1

By one CH₂ unit.

Draw the displayed formula of ethanol and circle its functional group.

Need a hint for Question 2?

Check carbon valency and identify the oxygen-containing group.

Check Question 2

Ethanol is CH₃CH₂OH. Show every C–H, C–C, C–O and O–H bond. Circle –OH.

Write the formula of the five-carbon alkane. Explain why ethanol is not a hydrocarbon.

Need a hint for Question 3?

Use CₙH₂ₙ₊₂; a hydrocarbon contains only two elements.

Check Question 3

C₅H₁₂. Ethanol contains oxygen as well as carbon and hydrogen.

Use Lesson 1 in your worksheet for written practice. Your teacher will discuss those answers in class.