isotopes , isobars and isotones

Symbolic Representation 


In the representation of an isotope or isobar of a given element, the mass number (A) is shown as the superscript at the head of the symbol of the element while the atomic no. (Z) is shown as the subscript at its bottom.

The symbolic representation of an isotope of an element ‘X’ has been shown below:

A = Mass number (protons + neutrons)
X = Symbol of the element
Z = Atomic number = Protons = electrons
e.g. ₈O¹⁶

O  is symbol of oxygen atom

8  is atomic no. of oxygen atom

16  is mass no. of oxygen atom

Isotope

Different kinds of atoms of the same element which have the same atomic no. but different mass nos. or atomic mass (or atomic weights) are called isotopes of that element. In other words, it can also be defined as different atoms of the same element which have same no. of protons but different no. of neutrons in their respective nuclei. Isotopes have identical chemical properties and differ slightly in their physical properties like densities, melting and boiling points.

examples of isotopes

Isotopes of oxygen- ₈O¹⁶, ₈O¹⁷, ₈O¹⁸

same atomic no. but different mass nos.

Isobars

The atoms of different elements which have the same mass no. but different atomic number are called isobars. These can also be defined as atoms of different elements which have the same sum of protons and neutrons in the nucleus of each of these atoms but different atomic number.

for example ₁₈Ar⁴⁰, ₁₉K⁴⁰, ₂₀Ca⁴⁰

have the same mass no. but different atomic number

Isotones

The atoms of different elements which have the same no. of neutrons but different atomic numbers are called isotones.

Example – ₆C¹⁴, ₇N¹⁵, ₈O¹⁶