# CH1 - Formulae and equations

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• Created by: zopetre_
• Created on: 12-04-17 18:40

## How to work out an ionic compound?

1) Write the symbols of the ions in the compound

2) Balance the ions so that the total number of + ions and - ions add to 0.

3) Write the formula without charges, put the number of ions of each element as a small number following/below the element symbol.

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## Rules of oxidation numbers

The oxidation number of an uncombined element is 0

The sum of the oxidation numbers in a compound is 0, in an ion it equals the overall charge

In compounds the oxidation numbers of Group 1 metals is +1 and Group 2 metals is +2

The oxidation number of oxygen is -2 in compounds except with fluorine or in peroxides

The oxidation number of hydrogen is 1 in compounds, except with metal hydrides

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## How to balance an equation?

1) Write a word equation

2) Write the symbols/formulae for the reactants and products

3) Balance the equation by multiplying formulae (if necessary)