When atoms of elements join together to form a compound, the resulting particles are molecules. Figure is an example of a molecule of water, consisting of 3 atoms put together.
The natural form of an element is known as the molecule of it. Therefore, an oxygen molecule is at times denoted by the symbol O2. The "O" represents oxygen, and the subscript 2 indicates that there are 2 atoms per molecule. The water molecule can be symbolized H2O, as there are 2 atoms of hydrogen and 1 atom of oxygen in each molecule.
Sometimes oxygen atoms are by themselves; then we denote the molecule as O. At times there are 3 atoms of oxygen grouped together. This is the gas called as ozone which has received much attention lately in environmental news. It is written O3.
All matter, whether it is liquid, solid, or gas, is made up of molecules. These particles are always keeps on moving. The speed with which they move is dependent on the temperature. The greater the temperature, the more quickly the molecules move around. In a solid, the molecules are interlocked in a sort of rigid pattern, although they continuously vibrate. In a gas, they are whizzing all over the place, bumping into each other and into solids and liquids adjacent to the gas.