nucleon number = mass number. This term indicates the total number of protons and neutrons combined in any elements.
Isotopes are elements that have the same number of protons but different number of neutrons.
Key ideas
From periodic table, the period number indicates the number of electron shells that an element will have. Elements in the same group will have the same number of electrons in the outer shell. These electrons are known as valence electrons.
In the context of electronic configuration, first shell needs 2 electrons, second shell needs 8 electrons and third shell also needs 8 electrons to be considered as full.
