1.14Unit 1. Structure, Bonding and Introduction to Organic Chemistry

Introductory Organic Chemistry — IAL Edexcel Modular (Chemistry) Revision Notes & Topical Questions

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Lesson summary

1.14 Introductory Organic Chemistry — IAL EDEXCEL MODULAR (CHEMISTRY) notes: Distinguish hazard from risk, recognise homologous series and functional groups, name and classify organic compounds, and identify structural isomers.Hazard = the inherent potential of a substance to cau…

Hazard symbols
Risk assessment
Control measures
Flammable substances
Procedure-specific precautions
Molecular formula

Section 1 of 10Hazard and risk

Hazard

Hazard the inherent potential of a substance to cause harm

Ethanol is flammable and hydrochloric acid is corrosive.

Risk

Risk the chance that the hazard causes harm in the way it is used

Eye protection does not change the hazard but it reduces the risk.

Hazard symbols

Hazard symbols flammable, corrosive, toxic, irritant or health hazard, oxidising, explosive, gas under pressure and dangerous to the environment

Section 2 of 10Risk assessments and control measures

1Risk assessment

Risk assessment identifies the hazards, considers how the substances are used, then states control measures
Factors include the amount used, whether it is heated, and the need for ventilation.

2Control measures

Control measures small quantities, fume cupboards for toxic vapours, eye protection, gloves, and keeping caps on bottles

3Flammable substances

Flammable substances heated with an electric heater or water bath and kept away from naked flames

4Procedure-specific precautions

Procedure-specific precautions stated for the actual step, for example HCl gas is produced so a fume cupboard is needed

Section 3 of 10Homologous series and functional groups

Homologous series and functional groups

Homologous series

Homologous series compounds with the same functional group and general formula, each member differing by CH₂

Members have similar chemical properties.
Physical properties change gradually, with boiling point rising with chain length.

Functional group

Functional group the atom or group of atoms that determines the chemical properties of the molecule

Family	General formula	Functional group	Suffix or prefix
Alkane	C_nH_2n+2	C–C	-ane
Alkene	C_nH_2n	C=C	-ene
Halogenoalkane	C_nH_2n+1X	C–X	chloro-, bromo-, iodo-
Alcohol	C_nH_2n+1OH	–OH	-ol
Aldehyde	—	–CHO	-al
Ketone	—	C=O inside the chain	-one
Carboxylic acid	—	–COOH	-oic acid

Section 4 of 10Types of formula

Types of formula

Molecular formula

Molecular formula the actual number of atoms of each element, for example C₂H₆O

Empirical formula

Empirical formula the simplest whole-number ratio of atoms

Structural formula

Structural formula shows the arrangement of atoms, for example CH₃CH₂OH

Displayed formula

Displayed formula shows every atom and every bond

Skeletal formula

Skeletal formula shows the carbon skeleton as lines, with functional groups labelled and hydrogens on carbon omitted

Section 5 of 10IUPAC nomenclature

Find the longest continuous carbon chain containing the functional group.

Choose the stem from the number of carbons: meth, eth, prop, but, pent, hex, hept, oct, non, dec.

Add the suffix for the principal functional group.

Number the chain from the end that gives the lowest numbers.

Name and number side chains as alkyl prefixes (-yl) in alphabetical order.

Use di-, tri- or tetra- for repeated groups, commas between numbers and hyphens between numbers and words.

Examples of names
- CH₃CH(CH₃)CH₂OH is 2-methylpropan-1-ol.
- CH₂=CHCH₂CH₃ is but-1-ene.

Section 6 of 10Classification of alcohols and halogenoalkanes

Classification of alcohols and halogenoalkanes

Primary

Primary the carbon bearing the functional group is attached to one other carbon

Secondary

Secondary the carbon bearing the functional group is attached to two other carbons

Tertiary

Tertiary the carbon bearing the functional group is attached to three other carbons

Effect on reactions

Effect on reactions tertiary alcohols resist oxidation
Butan-2-ol is secondary and 2-methylpropan-2-ol is tertiary.

Section 7 of 10Structural isomers

Structural isomers

Structural isomers compounds with the same molecular formula but different structural formulae

Chain isomerism

Chain isomerism the longest carbon chain differs because of branching
Pentane and 2,2-dimethylpropane are chain isomers.
C₄H₁₀ has 2 structural isomers and C₅H₁₂ has 3.

Positional isomerism

Positional isomerism the functional group is on different carbon atoms
Butan-1-ol and butan-2-ol are positional isomers.

Functional group isomerism

Functional group isomerism the isomers have different functional groups
Examples are an alcohol and an ether, an aldehyde and a ketone, and an alkene and a cycloalkane.

Branching and boiling point

Branching and boiling point branched isomers boil at lower temperatures
Less surface contact between molecules gives weaker London forces.

Section 8 of 10More from the specification

1Laboratory hazard mitigation of risks

Laboratory hazard mitigation of risks evaluating toxicity and using protective equipment mitigates chemical exposure risks during organic synthesis.

2Oxygen

A gas that relights a glowing splint.

Section 9 of 10Key terms

Term	Meaning
Hazard	A property of a substance that can cause harm.
Risk	The likelihood that a hazard will cause harm under the conditions of use.
Homologous series	A family of compounds with the same functional group and general formula, differing by CH₂.
Functional group	The atom or group of atoms responsible for the characteristic reactions of a compound.
Displayed formula	A formula showing every atom and every bond.
Skeletal formula	A formula showing the carbon skeleton as lines with functional groups shown.
Structural isomers	Compounds with the same molecular formula but different structural formulae.
Alkyl group	A side chain named by adding -yl to the alkane stem.

Section 10 of 10Exam technique

Confusing hazard with risk — the hazard is the property, and the risk depends on how the substance is used

Giving 'wear a lab coat and goggles' as a precaution — a precaution must be specific to the procedure

Numbering the chain from the wrong end — the functional group must get the lowest number

Listing side chains in numerical rather than alphabetical order

Counting rotation about a C–C bond as isomerism — structural isomers have different connectivity

Last updated: 15 October 2026