Chemical formulas are used to represent elements and compounds in chemical equations.
Each element can be represented by a unique chemical symbol, which is shown in the periodic table. A chemical symbol is always one or two letters. It starts with a capital letter and the following letter (if present) is lowercase.
For example, the chemical symbol for magnesium is ‘Mg‘.
The chemical formula for most elements is just their symbol. For example:
There are non-metal elements that exist as molecules, with two atoms joined together. They are represented by adding a subscript ‘2’ after the chemical symbol. For example:
Compounds can be represented by chemical formulae. The chemical formula of a compound includes:
For example, the chemical formula for carbon dioxide is CO2. This formula shows that the compound contains one carbon atom and two oxygen atoms. The subscript ‘2’ is used to show that there are two oxygen atoms.
Here are some examples of common compounds and their chemical formulae:
|Name of compound||Chemical Formula|
We can work out the formulae of simple ionic compounds if we know the charges of the ions. The charge of an ion is shown in superscript. Here are some examples of common ions and their charges.
|Name of ion||Charge|
We can predict the chemical formula of an ionic compound by using the formulae of the ions it contains. The positive and negative charges in the compound must balance, resulting in an overall charge of 0.
For example, if we want to determine the chemical formula of an ionic compound formed from the combination of sodium (Na+) and chloride (Cl–) ions, we can write the chemical formula as NaCl. The positive and negative charges in this compound balance, resulting in an overall charge of 0.
What is the chemical formula of magnesium chloride?