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Year 8 - Science

Chemical formulae

Atoms, elements and compounds

Unit Summary

This unit explores the basic atomic model, the differences between atoms, elements, and compounds, and the varying physical and chemical properties of elements. It covers chemical symbols, formulae, SI units, and IUPAC nomenclature, emphasising their use in describing elements and compounds.

Lesson Summary

You will learn to use chemical symbols to write down chemical formulae for elements and compounds.

Key Notes

  • The symbols for each element (each type of atom) a substance contains, appear in its chemical formula.
  • Numbers (subscripts) next to chemical symbols in a formula show the numbers of each type of atom in a compound.
  • Each compound contains a different combination of elements.
  • Some compounds contain the same elements as other compounds, but in a different ratio.

Vocabulary To Learn

  • chemical symbol: One or two letters used to represent a chemical element. The first letter is always a capital letter, e.g. Br represents bromine.
  • chemical formula: A representation of either the number of atoms or ratio of atoms of each element in a substance, e.g. H₂O is water = 2 x hydrogen + 1 x oxygen

Common Mistakes To Avoid

  • Writing subscript values as superscript values.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key points.

The symbols for each element (each type of atom) a substance contains, appear in its chemical formula. Numbers (subscripts) next to chemical symbols in a formula show the numbers of each type of atom in a compound.

2. Define this scientific word and use it in context. 'chemical symbol'

One or two letters used to represent a chemical element. The first letter is always a capital letter, e.g. Br represents bromine. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Writing subscript values as superscript values. Correction: Subscript values show the number of the atoms, while superscript in maths is used to square a value and so does not apply to chemical formulae.

More Lessons In This Unit

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