Organic Formulae (Cambridge (CIE) IGCSE Chemistry): Revision Note

Exam code: 0620 & 0971

Alexandra Brennan

Written by: Alexandra Brennan

Reviewed by: Stewart Hird

Updated on

Displayed formulae

  • Organic Chemistry is the scientific 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

  • Many of the structures you will be drawing are hydrocarbons

  • A hydrocarbon is a compound that contains only hydrogen and carbon atoms

  • Organic compounds can be represented in a number of ways:

    • Displayed Formulae

    • General Formulae

    • Structural Formulae

The displayed formula shows the spatial arrangement of all the atoms and bonds in a molecule

  • For example:

    The Structural Formulae of-2-methylbutane, downloadable IB Chemistry revision notes
  • This displayed formula tells us several things about the compound

    • It has 5 carbon atoms

    • It has 12 hydrogen atoms

    • It has only single bonds 

Structural formulae

Extended tier only 

  • In structural formulae, enough information is shown to make the structure clear, but most of the actual covalent bonds are omitted

  • Only important bonds are always shown, such as double and triple bonds

  • Identical groups can be bracketed together

  • Side groups are also shown using brackets

  • Straight chain alkanes are shown as follows:

Representing Condensed Structrual Formulae of Straight Chains, downloadable IB Chemistry revision notes

 

11-1-1-ethene-displayed-and-structural-formula

Structural isomers

  • Structural isomers are compounds that have the same molecular formula but different structural formulae

  • The molecular formula is the actual number of atoms of each element in a compound

  • Compounds with the same molecular formula can have different structural formulae due to the different arrangement of their atoms in space

  • Two examples of structural isomers are shown below 

Table showing structural isomerism in C4H10

11-1-1-structural-isomerism-table-c4h10

Table showing structural isomerism in C4H8

corrected-butene-isomers-rn-table

Examiner Tips and Tricks

Remember: Only double and triple bonds are shown in structural formulae.

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry Content Creator

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

Stewart Hird

Reviewer: Stewart Hird

Expertise: Chemistry Content Creator

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

Download notes on Organic Formulae