Writing Chemical Formulas: Elements, Valencies, and Examples

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Learn how to write chemical formulas by understanding the symbols of elements, their valencies, and following specific steps. Examples for writing formulas of compounds like ammonia and aluminum sulfate are provided to help you grasp the concept easily.

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Uploaded on Apr 19, 2025 | 1 Views

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Fomula 1

To write a Formula - the symbols of the elements/groups it is made up of, and -the valencies of the elements/groups it is made up of 2/10 TOPIC/COURSECODE-NAME/FACULTY/DEPT/COLLEGE 5/26/2020

The steps involved are as follows: 1.Write the symbols of the elements/groups side by side. Write their valencies on top as superscripts of their symbols. 2.Divide by any common factor in their valencies. 3.Interchange the numbers obtained and write them at the base (as subscripts) to get the formula. Let us understand this with the help of the following examples. 3/10 5/26/2020 TOPIC/COURSECODE-NAME/FACULTY/DEPT/COLLEGE

Writing the formula for ammonia 1.The elements in ammonia are nitrogen and hydrogen. The valency of nitrogen is 3 and that of hydrogen is 1. So, we write them as N3H1. 2.There is no common factor in the valencies 3 and 1. So, we move on to the third step. Interchanging the valencies and writing them as subscripts we get the formula of ammonia as NH3. 4/10 TOPIC/COURSE CODE-NAME/FACULTY/DEPT/COLLEGE 5/26/2020

Writing the formula for aluminium sulphate 1.It is made up of aluminium and sulphate. The valency of aluminium is 3 and that of the sulphate is 2. So, we write Al3(SO4)2. 2.The formula is Al2(SO4)3. 3.Notice that if a group contains two or atoms, then the group is put in brackets and the number is written as a subscript on the right of the bracket. 5/10 TOPIC/COURSE CODE-NAME/FACULTY/DEPT/COLLEGE 5/26/2020