# Organic Chemistry

> CIE IGCSE Chemistry · CIE IGCSE Chemistry (0620)
> Source: https://www.owlsprep.com/study/cie-0620-u11-overview/
> Weight: 15-20% of total exam marks (across MCQ, structured and alternative to practical papers)

This unit covers core organic chemistry concepts including homologous series, naming rules, key hydrocarbon groups, organic reactions, fuels, and synthetic polymers, a high-weight exam topic.

**Prerequisites:** [Covalent bonding and structure (Unit 4)](https://www.owlsprep.com/study/cie-0620-u4-overview/)

## Learning objectives

- Classify organic compounds by homologous series, name simple compounds using IUPAC rules, and draw their displayed, molecular and empirical formulae
- Explain the fractional distillation of crude oil and describe the properties, uses and environmental impacts of common hydrocarbon fuels
- Compare the structures, physical properties and characteristic reactions of alkanes, alkenes, alcohols and carboxylic acids
- Describe the formation, uses and environmental impacts of addition and condensation polymers

## Unit at a glance

We begin with foundational knowledge of organic compound classification, standard naming conventions, and different formula types used to represent organic molecules, before exploring the source of most industrial organic chemicals: crude oil, and how its useful fractions are separated via fractional distillation.

Next, we break down the structure, properties and characteristic reactions of the four core homologous series required for your syllabus, before concluding with the chemistry of synthetic and natural polymers, their production, uses and associated environmental challenges.

Work through the following subtopics in order to build your knowledge progressively:
- [Organic Families, Formulae and Naming](https://www.owlsprep.com/study/cie-0620-u11-organic-families-formulae-and-naming/) — Learn to classify organic compounds by homologous series, write multiple formula types, and name simple organic molecules using standard IUPAC rules.
- [Fuels and Fractional Distillation](https://www.owlsprep.com/study/cie-0620-u11-fuels-and-fractional-distillation/) — Explore the composition of crude oil, how fractional distillation separates its usable fractions, and the properties and uses of common hydrocarbon fuels.
- [Alkanes and Alkenes](https://www.owlsprep.com/study/cie-0620-u11-alkanes-and-alkenes/) — Compare the structure, bonding, properties and characteristic reactions of saturated alkanes and unsaturated alkenes, including addition reactions.
- [Alcohols and Carboxylic Acids](https://www.owlsprep.com/study/cie-0620-u11-alcohols-and-carboxylic-acids/) — Study the structure, properties and key reactions of alcohols and carboxylic acids, including the esterification reaction.
- [Polymers](https://www.owlsprep.com/study/cie-0620-u11-polymers/) — Discover how addition and condensation polymers form, their common real-world uses, and the environmental issues linked to plastic waste.

## Common pitfalls

- **Wrong:** Mixing up displayed, molecular and empirical formulae for organic compounds in exam answers
  - Why it fails: All three formula types are regularly assessed, and using the wrong type leads to avoidable lost marks
  - Correct: Practice writing all three formula types for every homologous series you study, and label them clearly in answers
- **Wrong:** Assuming all hydrocarbons will decolourise bromine water
  - Why it fails: Only unsaturated hydrocarbons with C=C double bonds (alkenes) undergo addition reactions with bromine; saturated alkanes do not react under standard conditions
  - Correct: Use the presence or absence of C=C double bonds to predict if a hydrocarbon will react with bromine water
- **Wrong:** Confusing addition and condensation polymerisation reactions
  - Why it fails: Both polymer types are examined, and their monomer structures and reaction products are distinct
  - Correct: Remember addition polymers form from alkene monomers with no by-products, while condensation polymerisation produces small by-products like water

## Cheatsheet

| Concept/Formula | Subtopic Reference | Key Use |
| --- | --- | --- |
| General alkane formula: $C_nH_{2n+2}$ | Alkanes and Alkenes | Predict molecular formula of any alkane from its carbon count |
| General alkene formula: $C_nH_{2n}$ | Alkanes and Alkenes | Predict molecular formula of any alkene from its carbon count |
| Alcohol functional group: -OH | Alcohols and Carboxylic Acids | Identify alcohol series and predict their characteristic reactions |
| Carboxylic acid functional group: -COOH | Alcohols and Carboxylic Acids | Identify carboxylic acid series and predict their characteristic reactions |
| Fractional distillation separates crude oil fractions by boiling point | Fuels and Fractional Distillation | Explain how useful industrial organic feedstocks are obtained from crude oil |
| Addition polymers form from alkene monomers with no by-products | Polymers | Predict polymer structure from given monomer and vice versa |

## What's next

Now that you understand the scope and structure of this Organic Chemistry unit, start with the first subtopic to learn how organic compounds are classified, named and represented using standard chemical formulae. Mastering these foundational rules will make it much easier to understand the reactions and properties of the different homologous series covered later in the unit. After completing all subtopics here, you will progress to the Chemical Analysis unit.

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