GCSE · Chemistry · AQA · Spec 8462

Atoms, elements and compounds

Element or compound?

ElementvsCompound

Start with the distinction that everything else on the page depends on.

Focus

What it contains

Element

An element is represented through its atoms and their chemical symbol.

Compound

A compound contains two or more elements chemically combined in fixed proportions.

The insight

An element and a compound are not interchangeable: a compound contains chemically combined elements.

How it is represented

Element

Atoms of an element are represented by a chemical symbol, such as O or Na.

Compound

A compound can be represented by a formula using the symbols of its atoms.

How compounds arise

Element

Elements are the starting substances from which compounds can be formed.

Compound

Compounds are formed from elements by chemical reactions.

Separating back to elements

Element

The element is already an element.

Compound

A compound can only be separated into its elements by chemical reactions.

From atoms to chemical equations

Follow the language of chemistry from the smallest idea to a complete reaction.

  1. Start with atomsAll substances are made of atoms, and an atom is the smallest part of an element that can exist.
  2. Give elements symbolsEach element is represented by a chemical symbol, allowing atoms and elements to be written compactly.
  3. Combine elements chemicallyChemical reactions form compounds from elements and always produce one or more new substances.
  4. Write compound formulaeFormulae use element symbols to represent compounds whose elements are chemically combined in fixed proportions.
  5. Represent the reactionReactions can be written as word equations or using formulae in balanced chemical equations.
  6. Extend at Higher TierHigher Tier students also write balanced half equations and ionic equations where appropriate.

The chemistry skills ladder

Different representations ask you to do different jobs.

Core language

These definitions hold the topic together.

Predict, then check

Decide what the information actually tells you before revealing the explanation.

You are shown a formula containing symbols for two different elements. What can you conclude if it represents a compound?

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Build from atoms and symbols to compounds, reactions and chemical equations.

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