Isotopes of some common elements are:

Practically every element consists of a mixture of several isotopes. The relative abundance of different isotopes differs from element to element. For example chlorine is composed of two isotopes. Their relative abundances are 75.4 and 24.6 percent respectively. The isotope can occur either naturally or can be produced artificially in the laboratory.

 Characteristics of Isotopes:

• The nuclei of these atoms have same number of protons but different number of neutrons.
• All isotopes of an element have the same number of valence electrons thus have identical chemical properties.
• The physical properties of the isotopes are different due to the difference in the number of neutrons in their nuclei.

Stability of Isotopes:

Many elements have isotopes but for most elements only one or two isotopes are stable. Stability of isotopes is affected by the ratio of neutrons to protons.

For stable isotopes of light elements, the number of neutrons will be almost equal to the number of protons. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which modifies this trend. Thus, there are no stable nuclei with equal proton and neutron numbers above atomic number Z = 20 (calcium); and as Z increases toward the heaviest nuclei, the ratio of neutrons per proton required for stability increases to about 1.5. The element tin (Sn) has the most stable isotopes with 10.