Essentially, atoms are the most basic unit of matter, comprising of a proton, neutron and an electron. Protons and neutrons together form a nucleus. The electrons revolve around the nucleus. Protons, as the name suggests, are positively charged, electrons are negatively charged and neutrons are neutral subatomic particles.
Atomic radius is measured in nanometres.
1/109 m = 1 nm
1 m = 109 nm