Edexcel IAL Chemistry · Unit 1
Introductory Organic Chemistry
Big idea: Every organic molecule is really just a carbon "skeleton" wearing a
small, specific tag called a functional group — and that tag is what decides
almost everything about how the molecule looks, reacts, and gets named.
Summary — What This Chapter Covers
Before we dive in, here's the map. This chapter builds the "vocabulary and grammar" of organic
chemistry — the naming rules, hazard awareness, and classification systems you'll use in
every single organic topic from here on. Get this chapter rock-solid and the rest of the
course gets dramatically easier.
Hazards & Risks
The difference between a hazard (fixed property) and a risk (how likely harm actually is), plus the standard hazard symbols.
Functional Groups & Homologous Series
Families of compounds that share a reactive "tag" and a predictable pattern as they grow.
Nomenclature & Classification
The IUPAC naming system — turning a structure into a name and a name back into a structure.
Structural Isomerism
Same molecular formula, different arrangement — chain isomers and positional isomers.
1. Hazards & Risks
This sounds like a "boring safety" topic, but examiners LOVE testing it because students
consistently mix up two words that sound almost identical: hazard and
risk. Get the distinction crystal clear and you'll never lose a mark on it again.
Hazard vs. Risk — the core distinction
Think of it like this: a shark in the ocean is a hazard — it has sharp teeth and could
hurt you, no matter where it is or what you're doing. Whether you're actually in danger from it
depends on the risk — are you swimming in that ocean right now, how close is it, are you
doing anything to protect yourself? Same shark, wildly different risk depending on the situation.
Definitions
Hazard = an inherent property of a substance that could cause harm (this never changes, no matter how you use it).
Risk = the chance that the hazard will actually cause harm, given how you're using it (this changes with your actions).
The textbook's own example is a great one: hydrochloric acid is corrosive — that's its
hazard, and it's true whether the acid is sealed in a cupboard or splashed
across a bench. Wearing eye protection doesn't make the acid any less corrosive (the hazard is
unchanged) — but it massively lowers the chance the acid actually reaches your eyes (the
risk goes down).
Quick way to remember
Hazard = "what could go wrong" (fixed). Risk = "how likely is it to actually go wrong, right now" (controllable).
Hazard warning symbols
You need to recognise these on sight — exams will show you the diamond symbol and expect you
to name the hazard and explain what it means in context.
| Symbol meaning | What it tells you |
|---|
| Health hazard (exclamation mark) | Can cause skin rashes, eye damage, or harm if ingested |
| Corrosive | Can cause skin burns and permanent eye damage |
| Flammable | Can catch fire if heated or exposed to a flame |
| Acute toxicity (skull & crossbones) | Can cause life-threatening effects even in small quantities |
| Oxidising | Can supply oxygen to fuel fires or cause explosions |
| Dangerous to the environment |
| Gas under pressure |
| Explosive |