Question

Define the terms nucleus, nucleons, atomic number, mass number, nuclide, isotopes, isobars, isotones and isomers.

Answer 1

Nucleus: A nucleus consists of protons and neutrons and the size of nucleus is about 10^-14 m. The protons and neutrons inside the nucleus go on interchanging to each other and hence called nucleons (i.e. protons or neutrons).

Nucleons: Protons and neutrons inside the nucleus of an atom are called nucleons.

Atomic number (Z): The number of protons in the nucleus is called atomic number of the element.

Mass number (A): Total number of nucleons in the nucleus is called mass number i.e. A = Z + N, so number of neutrons in the nucleus N = A - Z.

Nuclide: A nuclide is a specific nucleus of an atom characterised by its atomic number Z and mass number A Symbolically, nuclide is represented by _ZX^A

Isotopes: The atoms of an element which have same atomic number but different mass number are called isotopes, e.g. ₈O¹⁶, ₈O¹⁷,₈O¹⁸ are three isotopes of oxygen and ₁₇Cl³⁵, ₁₇Cl³⁷ are two isotopes of chlorine.

Isobars: The atoms having the same mass number but different atomic number are called isobars e g. ₁₈Ar⁴⁰, ₂₀Ca⁴⁰ and ₁H³, ₂H³. Isobars have the same numbers of nucleons.

Isotones: Atoms whose nuclei have the same number of neutrons are called isotones e.g. ₁₇Cl³⁷ and ₁₉Cl³⁹.

Isomers: The nuclei have the same atomic number and same mass number but in different energy states are called isomers e.g. a nucleus in its ground state and the identical nucleus in metastable excited state are isomers.