The nucleus of an atom contains three basic particles, the electron, the proton and the neutron.
The proton and neutron from the core of the atom called NUCLEUS
The mass of an atom is concentrated in the nucleus, and the diameter of the nucleus is about 10-15m in diameter
The neutron has no charge while the proton is positively charged with a mass of 1.67 x 10-27 kg
The proton number (Z) is the total number of protons present in the nucleus of an atom
The mass number (A) is the total number of protons and neutrons present in the nucleus of an atom. It is also called nucleon number
Nuclide: This is an atom with proton number and nucleon number specified. It is represented by \( \scriptsize _{A} ^{Z} \textrm {X} \)
Where X represents an element
   A = nucleon or mass numberÂ
   Z = atomic or proton number
Examples are \( \scriptsize _{2} ^{4} \textrm {H}, \; _{1} ^{3} \textrm {H}, \; _{8} ^{16} \textrm {0} \)
Isotopes
Isotopes are elements with the same atomic or proton number but different mass or nucleon number. Isotopes of the same elements have the same chemical properties due to the same number of protons.
Examples of isotopes are: \( \scriptsize _{6} ^{12} \textrm {C}, \; _{6} ^{14} \textrm {C}, \; _{8} ^{16} \textrm {0}, \; _{8} ^{17} \textrm {0}, \; _{17} ^{35} \textrm {Cl}, \; _{17} ^{37} \textrm {Cl} \)
Learnt a lot from here