Organic chemistry is the study of carbon compounds, and in IGCSE Chemistry it starts with a small set of families and a few rules for reading them. Once you can spot the functional group, count bonds and use the general formulae, most structure questions become routine.
Questions range from naming a structure to deciding whether two molecules are isomers or explaining a test result.
What should you know before starting?
You need covalent bonding, especially that carbon forms four bonds, which bonding and structure covers. You also need to read and write formulae with subscripts, which formulas and equations develops. The equation balance reasoning trainer is a quick way to rebuild the atom-counting habit.
An orienting example
Take the structure CH₃CH₂CH₂OH. It contains carbon, hydrogen and one oxygen in an -OH group, so it belongs to the alcohol family. It has three carbons, so the stem is prop and the name is propanol.
Counting atoms gives 3 carbons, 3 + 2 + 2 + 1 = 8 hydrogens and 1 oxygen, so the molecular formula is C₃H₈O. A second structure, CH₃CH(OH)CH₃, has the same formula with the -OH on the middle carbon, so the two are isomers.
One structure gave a family, a name, a formula and a link to another molecule. Each lesson below takes one of those steps slowly.
In what order should you study the lessons?
- Identify a functional group in a structure: learn what to scan for, C=C, -OH or -COOH.
- Distinguish homologous family from isomer: separate two ideas that are often mixed up.
- Draw a small molecule with correct bonding: use the bond counts to draw displayed formulae.
- Recognise saturated and unsaturated structures: link the double bond to the formula pattern.
- Convert between formula representations within scope: move between molecular, structural and displayed forms.
Then test yourself with the organic families and naming practice set.
What are the common traps?
- Calling CH₃COOH an alcohol because it ends in OH. The C=O on the same carbon makes it a carboxylic acid.
- Calling two molecules isomers because they are in the same family. Isomers need the same molecular formula.
- Drawing a carbon with five bonds, or leaving out a hydrogen.
- Forgetting the hydrogen in -OH or -COOH when counting.
- Saying unsaturated means “more hydrogens”. It means a C=C and fewer hydrogens.
- Assuming a formula gives one structure. One molecular formula can fit more than one isomer.
How should you use the practice set?
Work through the practice questions on paper and draw each structure rather than only reading it. Mark each error by type, not by question number. The mistake log and retest queue helps you track which slip keeps returning.
The mole and equation-ratio tutor supports later calculations that use these formulae. The next module, organic reactions, builds directly on the families named here.
Some students can recite the definitions but lose marks on drawings and wording. Online one-to-one Chemistry tuition gives a teacher the chance to read your own structures and explanations and respond to exactly what you wrote.