Question

(a) What are isotopes?
(b) State modern periodic law.
(c) Name two noble gas.

Answer 1

A. In a given element, the number of neutrons can be different from each other, while the number of protons is not. These different variants of the same element are called isotopes. Isotopes are atoms with the same number of protons but that have a different number of neutrons. Since the atomic number is equal to the number of protons and the atomic mass is the sum of protons and neutrons, we can also say that isotopes are elements with the same atomic number but different mass numbers.

B. The modern periodic law states that the physical and chemical properties of the elements are the periodic function of their atomic numbers. It means that if the elements are arranged in order of increasing atomic numbers, the elements with similar properties recur after regular intervals.

C. $Helium\left(He\right),$ $Argon\left(Ar\right)$ $and$ $Neon\left(Ne\right),etc.$