Overview
This lecture covers part two of IGCSE Organic Chemistry, focusing on how to name organic compounds and how to interpret their chemical and displayed formulas.
Naming Organic Compounds
- Organic compound names tell you the homologous series and the number of carbon atoms.
- Homologous series include alkanes, alkenes, alcohols, and carboxylic acids.
- Names ending in "-ane" are alkanes (e.g., ethane).
- Names ending in "-ene" are alkenes (e.g., ethene).
- Names ending in "-ol" are alcohols (e.g., ethanol).
- Names ending in "-oic acid" are carboxylic acids (e.g., ethanoic acid).
Carbon Atom Prefixes
- "Meth-" indicates 1 carbon atom.
- "Eth-" indicates 2 carbon atoms.
- "Prop-" indicates 3 carbon atoms.
- "But-" indicates 4 carbon atoms.
- "Pent-" indicates 5 carbon atoms.
- "Hex-" indicates 6 carbon atoms.
Recognizing Compounds from Formulas
- Alkanes: contain only single carbon-carbon bonds and no functional group.
- Alkenes: have a carbon-carbon double bond as a functional group.
- Alcohols: have an -OH (hydroxyl) group.
- Carboxylic acids: have a -COOH (carboxyl) group.
Examples of Naming and Drawing Formulas
- CH₄: One carbon, all single bonds, so "methane" (alkane).
- C₂H₄: Two carbons, double bond, so "ethene" (alkene).
- C₃H₇O: Three carbons, contains -OH, so "propanol" (alcohol).
- C₄H₇CO: Four carbons, contains -COOH, so "butanoic acid" (carboxylic acid).
Writing Displayed Formulas
- Methane (CH₄): one carbon, four hydrogens, only single bonds.
- Ethane (C₂H₆): two carbons, single bond between them, six hydrogens.
- Ethene (C₂H₄): two carbons, double bond, four hydrogens.
- Ethanol (C₂H₅OH): two carbons, five hydrogens, one -OH group.
- Ethanoic acid (CH₃COOH): two carbons, three hydrogens attached to one carbon, one -COOH group.
Key Terms & Definitions
- Homologous Series — A family of organic compounds with the same functional group and similar chemical properties.
- Functional Group — A specific group of atoms responsible for the characteristic reactions of a compound.
- Displayed Formula — A diagram showing all atoms and bonds in a molecule.
Action Items / Next Steps
- Practice naming and drawing displayed formulas for given organic compounds.
- Review the formulas for alkanes (CnH2n+2), alkenes (CnH2n), and alcohols (CnH2n+1OH).
- Prepare for next topic in organic chemistry.