Question

How is the atomic number of an element defined?

Answer 1

As we know that the atomic number of an element is represented by the symbol $'Z'$ and it is related to the number of protons and electrons present in an atom. An atomic number of any element is written at the lower script such as $_Z^AX$ where $A$ is mass number and $Z$ is atomic number.

Complete step-by-step answer:
We already know that the atomic number of unit positive charges on the nucleus of an atom of the element is known as the atomic number. So we can say the atomic number is equivalent to the number of protons which in turn is equivalent to the number of electrons present in an atom. An element is represented by its chemical symbol where the mass number is written on the superscript and atomic number is written on the subscript as shown $_Z{X^A}$.

We also know that there are also some more terms related to atomic numbers such as isotopes which are defined as the atoms of the same elements possessing the same number of protons, different mass numbers but they have similar atomic numbers. For instance: the three isotopes of hydrogen which are $_1^1H,_1^2D,_1^3T$.

The other term related to atomic number is called Isobars which are defined as the atoms of different elements possessing the same mass number but their atomic number is different. For example: the Argon, Potassium and calcium possessing same atomic number given as: $_{18}^{40}Ar,_{19}^{40}K,_{20}^{40}Ca$

Note: Always remember that the atomic number and mass number are two different terms where mass number is defined as the sum of total number of protons and neutrons of an atom whereas number of protons is equal to the atomic number of an atom.