Very often in the study of science, you shall come across many elements and compounds that are represented by letters and numbers. These symbols are written in a definite way to tell us what the elements and compounds are made up of. They also tell us the various amounts of atoms in any substance.
Every element has a symbol. For example — Fe stands for Iron, O stands for Oxygen and C stands for carbon. It is very important to know the correct symbols of all the elements, because if they are not written properly, they change the entire meaning of it.
For example CO means one element of carbon and one element of oxygen together. This is Carbon Monoxide. It is NOT the same as Co, which is the symbol for cobalt.
The small numbers below the symbols tell us how many atoms of that element are in the molecule. 'O' means one atom of oxygen. means 2 atoms of hydrogen. , means two atoms of Hydrogen and one atom of oxygen. This is a water molecule.
When molecules react with other molecules, they form more complex compounds, with complex chemical formulae.
Here is an example:
The symbol for Sulphur is S, the symbol sodium is Na and that for Oxygen is O. If the atoms of these three elements react, they form a compound such as (Sodium sulphate) This compound has 2 atoms of Na, 1 atom of S and 4 atoms of O. Compounds with this formulae will be exactly the same anywhere on earth because of its unique composition. The same can be said of (water molecule). If we use the chemical formulae , it will be the same anywhere on earth, BUT if we say water, it will not be the same anywhere on earth because water is generic and may contain other atoms of other elements in it.