Part 1 of organic chemistry notes for Edexcel IGCSE covering alkanes and their reactions, isomerism, fractional distillation and pollution. See part 2 for alkenes etc. and the rest of organic chemistry. Notes were made from the specification, so cover everything and have helped me achieve grade 9 -...
Organic Chemistry (Part 1 – Alkanes):
Homologous Series - a family of compounds represented by the same general formula
General formula - represents whole number ratios of atoms of different elements for a homologous series
Molecules in a homologous series contain the same functional group:
Functional group - atom or group of atoms that define the chemical properties of a homologous series
Hydrocarbon - compound contain hydrogen & carbon ONLY
Saturated - contains single bonds only
Unsaturated - contains double bond(s)
Crude oil - a mixture of hydrocarbons
Fraction - a mixture of hydrocarbons with similar boiling points
Structural isomerism – molecules with the same molecular formula and different displayed formula
Types of formula:
Type What it shows Example (of Butane)
General Whole number ratio of atoms in a homologous series CnH2n+2
Empirical Simplest whole number ratio of atoms of each element in a compound C2H5
Molecular Actual number of atoms of each element in a compound C4H10
Displayed Shows all bonds between atoms (diagram)
Structural Shows no bonds, but rather each compound, carbon by carbon CH3CH2CH2CH3
Prefixes based on the number of carbon atoms:
No. Of Carbon atoms 1 2 3 4 5 6 7 8 9 10
Prefix Meth- Eth- Prop- But- Pent- Hex- Hept- Oct- Non- Dec-
Features of a Homologous series:
• They display a gradual trend in physical properties
• Have similar chemical properties
• Represented by the same General Formula
• Contain the same Functional Group
• Differ by CH2 each time (shown by the structural formula)
ALKANES: a homologous series
• simplest family of hydrocarbons
• Saturated - atoms are connect by single covalent bonds
• General formula: CnH2n+2
• For every n number of carbon atoms, there are 2n+2 hydrogen atoms
• All alkane names end in '-ane'
• Burn in oxygen in combustion reactions
• Undergo substitution reactions (with halogens) in the presence of UV light
• The first 4 alkanes (Methane, ethane, propane, butane) are all gases at room temperature
No. Of carbon atoms Name Displayed formula Structural formula Molecular formula
1 Methane CH4 CH4
2 Ethane CH3CH3 C2H6
3 Propane CH3CH2CH3 C3H8
4 Butane CH3CH2CH2CH3 C4H10
, 5 Pentane CH3CH2CH2CH2CH3 C5H12
6 Hexane CH3CH2CH2CH2CH2CH3 C6H14
SUBSTITUTION REACTIONS:
E.g., Methane will react with Bromine in the presence of UV
light in a substitution reaction
Dot & cross diagram for Methane and bromine
- The structure type is simple molecular, with covalent
bonding
- In this reaction, a hydrogen atom in the alkane is replaced (substituted) by a halogen atom (in this case Bromine)
- The replaced hydrogen atom then forms a bond with the remaining halogen atom
In this example:
Another example: Reaction between Propane and chlorine in the presence of UV light.
NOMENCLATURE & ISOMERISM:
(structural) Isomers:
• Have the same number of atoms of each element
• 'iso' means 'same', like in 'isotopes'/'isometric
triangle'
• Can be described as a 'branched chain'
Carbon chains can be rearranged into structural isomers.
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