chemical formula

The use of chemical formula is a shorthand way of showing

1. the number and type atoms in a compound and
2. the number of atoms in a molecular element The chemical symbols of the elements are shown in the Periodic table. For example the element hydrogen is given the chemical symbol H and the element oxygen the chemical symbol O.
   In a chemical formula the chemical symbol of each element is shown with subscript numbers which tell us the numbers or ratio of atoms in the compound or molecular element.
   For example the compound water has the chemical formula H₂O. This tells us water is made up of two elements, hydrogen and oxygen. The subscript 2 in H₂O tells us there are two parts hydrogen to one part oxygen. Note: The subscript 1 is never but taken for granted. That is why water has the formula H₂O and not H₂O₁
   Some elements also exist as molecules. Molecules are groups of atoms joined together by chemical bonds. Molecular elements like compounds also have a chemical formula. Examples of molecular elements include hydrogen, H₂ and ozygen O₂.
   Hydrogen atoms are too unstable to exist by themseleves as free atoms. They pair up to with other hydrogen atoms to form hydrogen molecules which are much more stable. The chemical formula of the hydrogen molecule is therefore H₂. This means two hydrogen atoms are joined together. The molecule O₂ is also much more stable than single oxygen atoms.
   The combining power or valency of an element determines the ratio that atoms will combine with one another. A knowledge of valencies can help us predict the chemical formula of a substance. Atoms achieve a stable outer shell of electrons by transferring or sharing electrons. They always combine with one another n simple whle number ratios.