Determining ionic formulae
I can deduce the formulae of ionic compounds (including oxides, hydroxides, halides, nitrates, carbonates and sulfates) given the formulae of the constituent ions.
Determining ionic formulae
I can deduce the formulae of ionic compounds (including oxides, hydroxides, halides, nitrates, carbonates and sulfates) given the formulae of the constituent ions.
Lesson details
Key learning 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.
- 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.
Common misconception
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.
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.
Keywords
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).
Equipment
None required.
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Video
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Starter quiz
6 Questions
The electrostatic force of attraction between oppositely charged ions.
The regular arrangement of atoms or ions in a 3D space.
Atom or molecule with a charge due to the gain or loss of electrons.
Exit quiz
6 Questions
Simplest whole number ratio of atoms of each element in a compound.
Shows the actual number of atoms of each element in a compound.
Ions made of more than one type of atom.
Name ending for a compound with a metal and singular non–metal.
Name ending for a compound with 3 or more elements, one being oxygen.
