how to calculate the chemical formulas of compounds
Hi Kartik,
Chemical formula of a compound is the symbolic representation of its atomic constituents. In other words, a chemical formula represents the composition of a molecule in terms of the symbols of the elements present in that molecule.
To write the chemical formula of a compound, one should have prior knowledge of two things: 1. The symbols of the constituent elements, and 2. The combining capacity of each atom constituting the compound |
The number of atoms of other elements with which one atom of an element combines is decided by the valency of that element.
For example, both hydrogen and chlorine have a valency of 1. Therefore, one atom of hydrogen reacts with one atom of chlorine to form one molecule of hydrogen chloride.
The valency of an ion is equal to the charge on it.
While writing the chemical formula, certain rules need to be kept in mind. These rules are given below:
i. The valencies or charges on the ions must be balanced.
ii. In case of a compound consisting of a metal and a non-metal, the symbol of the metal is written first. For example, in calcium chloride (CaCl2) and zinc sulphide (ZnS), calcium and zinc are metals, so they are written first, whereas chlorine and sulphur are non-metals.
(iii) In case of compounds consisting of polyatomic ions, the polyatomic ions are enclosed in a bracket before writing the number to indicate the ratio. For example, in aluminium sulphate
[Al2 (SO4)3], the polyatomic sulphate ion is enclosed in a bracket before writing the subscript 3.
For example:
Formula of calcium oxide
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Thus, the chemical formula of calcium oxide is CaO.
Hope it is clear to you.
Best Wishes!