What is the Homologous Series?
The homologous series consists of a family of organic compounds with the same general formula and similar chemical properties because they have the same functional group.
General characteristic of a Homologous Series
- Same functional group
- Similar chemical properties
- Each member of the series differ from the next by an additional —CH₂— unit
- There is gradual change in their physical properties as we go down the series from 1 member to the next.
Prefix for the number of carbon atoms
Meth- 1
Eth- 2
Prop- 3
But- 4
Suffix for homologous series
-ane: Alkane
-ene: alkene
-ol: alcohol
-oic acid: carboxylic acid
Alkanes
Hydrocarbons that contain only carbon-carbon single bonds and carbon hydrogen bonds. (Saturated hydrocarbons)
General characteristics of Alkanes
- No functional groups
- Generally have the general formula: CₙH₂ₙ₊₂
- Are called saturated hydrocarbons
Low melting and boiling points (Alkanes & Alkenes)
- Covalent compounds with simple molecular structure, little amount of energy is needed to overcome the weak intermolecular forces of attraction between alkane molecules. Hence low melt and boiling point.
- melting and boiling points increase as the molecular size of the alkanes increases. > forces of attraction between the alkanes molecules also increase
Viscosity of alkanes / alkenes
More viscous as the molecular size of the alkanes/ alkenes increases / number of carbon atom increases.
Solubility of alkanes
Insoluble in water.
Soluble in organic solvents
Flammability of alkanes /alkenes
Less flammable as the molecular size of alkanes/ alkenes increases
Smokier flame caused by incomplete combustion of alkanes/ alkene molecules
Chemical reaction of alkanes
Generally unreactive as they consist of strong carbon-carbon single bonds and strong CH bonds
Complete combustion reaction of alkane/ Alkene
Complete: alkanes/ alkene burn readily in excess air to produce carbon dioxide and water vapour
Incomplete combustion of alkane/ alkenes reaction
Insufficient oxygen = incomplete combustion.
Instead of co2, carbon monoxide and soot is produced
- However, alkenes are more likely to undergo incomplete combustion
Combustion of alkanes and alkenes are…
Highly exothermic
Alkanes react with halogens in the presence of…
Ultraviolet light
Order when balancing equation
Carbon
Hydrogen
Oxygen
Alkenes
Hydrocarbons that contain carbon-carbon double bonds (unsaturated hydrocarbons)
General characteristics of alkene
- Functional group is carbon-carbon double bond.
- General formula : CnH₂n
Solubility of alkene
Insoluble in water
Soluble in most organic solvents
