Atomic Number: Atomic number of an element is equal to the number of protons present in the nucleus of an element.
Atomic number = number of protons in one atom of element.
Since the atom as a whole is neutral therefore atomic number is the same as the number of electrons around the nucleus of an atom. Atomic number of an element does not change during chemical reaction, it remains the same.
Mass number: The total number of protons and neutrons present in one atom of an element is known as its mass number.
Mass number = no. of protons + no. of neutrons.
