Question

Define the following terms :

(a) Atomic number

(b) Mass number

(c) Nucleons

(d) Valence shell

Answer 1

(a) Atomic number: Atomic number refers to the number of protons present in an atom. It is denoted by
Z. Example: An atom of oxygen contains 8 proton Therefore its atomic number is 8.
(b) Mass number: Mass number refers to the sum of the number of protons and neutrons present in
the nucleus of an atom and denoted by A Mass number = Number of protons + Number of neutrons.
(c) Nucleons: The protons and neutrons collectively are known as nucleons.
(d) Valence Shell: The outermost shell of an atom is known as its valence shell.