National 5 Chemistry
Unit 2 Nature’s Chemistry
Summary Notes
, Topic 1
Homologous Series
2
, Learning Outcomes
Systematic carbon chemistry
A homologous series is a family of compounds with the same general formula and similar chemical
properties.
Patterns are often seen in the physical properties of the members of a homologous series.
The subsequent members of a homologous series show a general increase in their melting and
boiling points. This pattern is attributed to increasing strength of the intermolecular forces as the
molecular size increases. The type of intermolecular force does not need to be identified.
Hydrocarbons are compounds containing only hydrogen and carbon atoms.
Compounds containing only single carbon–carbon bonds are described as saturated.
Compounds containing at least one carbon–carbon double bond are described as unsaturated.
It is possible to distinguish an unsaturated compound from a saturated compound using bromine
solution. Unsaturated compounds decolourise bromine solution quickly.
The structure of any molecule can be drawn as a full or a shortened structural formula.
Isomers:
- are compounds with the same molecular formula but different structural formulae
- may belong to different homologous series
- usually have different physical properties
Given a structural formula for a compound, an isomer can be drawn.
Isomers can be drawn for a given molecular formula.
Alkanes
Are a homologous series of saturated hydrocarbons
Are commonly used as fuels
Are insoluble in water
Can be represented by the general formula CnH2n+2
Straight-chain and branched alkanes can be systematically named from structural formulae
containing no more than 8 carbons in the longest chain.
Molecular formulae can be written and structural formulae can be drawn, from the systematic
names of straight-chain and branched alkanes, containing no more than 8 carbons in the longest
chain.
3
, Cycloalkanes
Are a homologous series of saturated, cyclic hydrocarbons
Are used as fuels and solvents
Are insoluble in water
Can be represented by the general formula CnH2n
Cycloalkanes (C3–C8) can be systematically named from structural formulae. Branched cycloalkanes
are not required.
Molecular formulae can be written and structural formulae can be drawn from the systematic
names of un-branched cycloalkanes.
Alkenes
Are a homologous series of unsaturated hydrocarbons
Are used to make polymers and alcohols
Are insoluble in water
Contain the C=C double bond functional group
Can be represented by the general formula CnH2n
Straight-chain and branched alkenes can be systematically named indicating the position of the
double bond, from structural formulae containing no more than 8 carbon atoms in the longest
chain.
Molecular formulae can be written and structural formulae can be drawn, from the systematic
names of straight-chain and branched alkenes, containing no more than 8 carbons in the longest
chain.
Chemical equations can be written for the addition reactions of alkenes, using molecular or
structural formulae.
Alkenes undergo addition reactions:
- with hydrogen forming alkanes, known as hydrogenation
- with halogens forming dihaloalkanes
- with water forming alcohols, known as hydration
4
Unit 2 Nature’s Chemistry
Summary Notes
, Topic 1
Homologous Series
2
, Learning Outcomes
Systematic carbon chemistry
A homologous series is a family of compounds with the same general formula and similar chemical
properties.
Patterns are often seen in the physical properties of the members of a homologous series.
The subsequent members of a homologous series show a general increase in their melting and
boiling points. This pattern is attributed to increasing strength of the intermolecular forces as the
molecular size increases. The type of intermolecular force does not need to be identified.
Hydrocarbons are compounds containing only hydrogen and carbon atoms.
Compounds containing only single carbon–carbon bonds are described as saturated.
Compounds containing at least one carbon–carbon double bond are described as unsaturated.
It is possible to distinguish an unsaturated compound from a saturated compound using bromine
solution. Unsaturated compounds decolourise bromine solution quickly.
The structure of any molecule can be drawn as a full or a shortened structural formula.
Isomers:
- are compounds with the same molecular formula but different structural formulae
- may belong to different homologous series
- usually have different physical properties
Given a structural formula for a compound, an isomer can be drawn.
Isomers can be drawn for a given molecular formula.
Alkanes
Are a homologous series of saturated hydrocarbons
Are commonly used as fuels
Are insoluble in water
Can be represented by the general formula CnH2n+2
Straight-chain and branched alkanes can be systematically named from structural formulae
containing no more than 8 carbons in the longest chain.
Molecular formulae can be written and structural formulae can be drawn, from the systematic
names of straight-chain and branched alkanes, containing no more than 8 carbons in the longest
chain.
3
, Cycloalkanes
Are a homologous series of saturated, cyclic hydrocarbons
Are used as fuels and solvents
Are insoluble in water
Can be represented by the general formula CnH2n
Cycloalkanes (C3–C8) can be systematically named from structural formulae. Branched cycloalkanes
are not required.
Molecular formulae can be written and structural formulae can be drawn from the systematic
names of un-branched cycloalkanes.
Alkenes
Are a homologous series of unsaturated hydrocarbons
Are used to make polymers and alcohols
Are insoluble in water
Contain the C=C double bond functional group
Can be represented by the general formula CnH2n
Straight-chain and branched alkenes can be systematically named indicating the position of the
double bond, from structural formulae containing no more than 8 carbon atoms in the longest
chain.
Molecular formulae can be written and structural formulae can be drawn, from the systematic
names of straight-chain and branched alkenes, containing no more than 8 carbons in the longest
chain.
Chemical equations can be written for the addition reactions of alkenes, using molecular or
structural formulae.
Alkenes undergo addition reactions:
- with hydrogen forming alkanes, known as hydrogenation
- with halogens forming dihaloalkanes
- with water forming alcohols, known as hydration
4
