Organic Compounds

  • Organic chemistry is the study of the structure, properties, and reactions of organic compounds. 
  • Organic compounds are those which contain carbon
  • For conventional reasons metal carbonates, carbon dioxide and carbon monoxide are not included in organic compounds.
  • The names of organic compounds have two parts: the prefix or stem and the suffix or end part.
  • The prefix tells you how many carbon atoms are present in the longest continuous chain in the compound.
  • The suffix tells you what functional group is on the compound.

Organic compounds naming table, Edexcel GCSE Chemistry

Further Rules for Naming Compounds

  • When there is more than one carbon atom where a functional group can be located it is important to distinguish exactly which carbon the functional group is on. 
  • Each carbon is numbered and these numbers are used to describe where the functional group is.
  • Numbering begins at the end of the molecule that produces the smallest number in the name.
  • E.g. below are two molecules of butene with the C=C bond at different ends of either chain.
  • Numbering assigns the double bond to the carbon atom that produces the lowest number, hence both molecules are named but-1-ene.

But-1-ene (a), Edexcel GCSE Chemistry

Numbering begins on the left of this molecule

Numbering begins on the right of this molecule

  • When 2 functional groups are present di- is used as a prefix to the second part of the name. 
  • Branching also needs to be considered, the carbon atoms with the branches are described by their number.
  • When the location of functional groups and branches needs to be described the functional group takes precedence so the functional group has the lowest number.

Alkanes

Specification Point 9.10C:
  • Recall the formulae of molecules of the alkanes, methane, ethane, propane and butane, and draw the structures of these molecules, showing all covalent bonds
  • Alkanes are a homologous series of hydrocarbon compounds with the general formula:

CnH2n+2

  • E.g. an alkane with 6 carbon atoms therefore has (6 x 2) + 2 = 14 hydrogen atoms.
  • They can be represented by their molecular formula or displayed formula.
  • The lines in between the atoms in displayed formulae represent covalent bonds.
  • They are colourless compounds which have a gradual change in their physical properties as the number of carbon atoms in the chain increases.
  • Alkanes are generally unreactive compounds but they do undergo combustion reactions, can be cracked into smaller molecules and react with halogens in the presence of light.

Alkane formulae & covalent bond table, Edexcel GCSE Chemistry

Saturation in Hydrocarbons

Specification Point 9.11C:
  • Explain why the alkanes are saturated hydrocarbons
  • Alkanes contain only single bonds between the carbon atoms, there is no carbon carbon (C=C) double bond present.
  • This means that alkanes form bonds with as many atoms as they can, hence the term saturated, since no more atoms can be added to an alkane.

Need help?

Edexcel GCSE Chemistry Notes

Want to aim for a Level 9?

See if you’ve got what it takes. Test yourself with our topic questions.

Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.