3. Atoms & Molecules
All the matter is made up of atoms. An atom is the smallest particle of an element that can take part in a chemical reaction. Atoms of most of the elements are very reactive and do not exist in the free state. They exist in combination with the atoms of the same element of another element.
Atoms are very, very small in size. The size of an atom is indicated by its radius which is called ‘atomic radius’. Atomic radius is measured in ‘nanometres’. The symbol of a nanometre is nm.
1 nanometre =
or 1 nm =
or 1 nm = 10–9
Hydrogen atom is the smallest atom of all. They cannot be viewed by simple optical microscopes. However, through modern techniques such as scanning tunneling microscope it is possible to produce magnified images of surfaces of elements showing atoms.