Crisscross method
The crisscross method is a method of finding out the chemical formula of a metal and non-metal that combine to form an ionic bond.[1]
To use this method, the absolute value of the oxidation number of the first ion is used as the subscript of the second, and vice versa. The subscripts are then reduced by the greatest common factor. For instance, to find the formula for aluminium oxide:
- The oxidation number of Al is +3 and oxygen is -2. Crisscross the absolute values to give Al2O3
To find the formula for magnesium oxide:
- The oxidation number of Mg is +2 and oxygen is -2. Crisscross the absolute values to give Mg2O2
- In this example there is a common factor of 2 so divide by 2 to give MgO
This method is often used to convert between ionic compounds and chemical formulas
References[edit]
- ↑ Sharon Bewick; Jonathan Edge; Therese Forsythe; Richard Parsons (2011). CK12 Chemistry. CK-12 Foundation. pp. 348–349. GGKEY:J8HDA9JYCCN. Retrieved 25 March 2011. Search this book on
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