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Year 10 - Science

Determining ionic formulae

Structure and bonding

Unit Summary

This unit explores changes of state, particle kinetics, and energy transfers in relation to chemical bonding, including ionic, covalent, and metallic bonds. It examines carbon's unique bonding properties, leading to organic compounds and materials like diamond, graphite, fullerenes, and graphene.

Lesson Summary

You will learn to deduce the formulae of ionic compounds (including oxides, hydroxides, halides, nitrates, carbonates and sulfates) given the formulae of the constituent ions.

Key Notes

  • An empirical formula is the simplest whole number ratio of atoms of each element in a compound.
  • The formula of an ionic compound is an empirical formula, as there is no definite quantity of each ion.
  • Ionic compounds ending with "–ide" only contain a metal and a non–metal ion.
  • Polyatomic ions are ions that are made up of more than one type of atom.
  • Ionic compounds ending with "–ate" always contain at least three elements, one of which is oxygen.

Vocabulary To Learn

  • empirical formula: The simplest whole number ratio of atoms of each element in a compound.
  • polyatomic ions: Ions that are made up of more than one type of atom.
  • "–ide": The name ending for a compound with a metal and non–metal present, for example, potassium iodide (KI).
  • "–ate": The name ending for a compound with three or more elements present (one of which is oxygen), for example, potassium sulfate (K₂SO₄).

Common Mistakes To Avoid

  • Using ionic charges to determine the empirical formulae, especially with polyatomic ions. Standard notation is difficult and confusing, e.g. when to use superscripts, subscripts or brackets.

3 Quick Questions (With Answers)

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

An empirical formula is the simplest whole number ratio of atoms of each element in a compound. The formula of an ionic compound is an empirical formula, as there is no definite quantity of each ion.

2. Define this scientific word and use it in context. 'empirical formula'

The simplest whole number ratio of atoms of each element in a compound. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Using ionic charges to determine the empirical formulae, especially with polyatomic ions. Standard notation is difficult and confusing, e.g. when to use superscripts, subscripts or brackets. Correction: At this stage, pupils will need to just learn the the formulae of the polyatomic ions and accept that a full explanation will come later in their chemistry learning. Provide pupils with plenty of practice of writing and using ionic formulae.

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