Atom

atom

basic unit of matters, consists of nucleus surrounded by a cloud of negatively charged electrons

where is the nucleus?

is at the centre of the atom and contains the protons and neutrons

nucleons

protons and neutrons are collectively known as the nucleons

the mass of the atom

is concentrated in the nucleus

nuclide

group of atoms with the same protons number and the same nucleon number

isotopes

group of atoms with the same protons number but different nucleon numbers