Atomic number: The number of unit positive charges (or protons) present in the nucleus of an atom of a particular element is called the atomic number of that element. Furthermore, the number of protons is exactly equal to the number of electrons present in a neutral atom. Atomic number is represented by Z. Thus Atomic Number (Z) = Number of Protons = Number of Electrons, in a neutral atom The atomic number is represented by putting ‘Z’ in subscript on the left-hand side of the symbol of the element, for e.g., 2He for helium as He has only two protons in its nucleus. Similarly, for the atomic number of potassium is 19, it means that the potassium atom has 19 protons and 19 electrons in its neutral atom and is depicted by K.
