Isotopes and Isobars
Isotopes are defined as the atoms of the same element, which have the same atomic number but different mass numbers. For example, take the case of hydrogen atom, it has three atomic species, namely protium ( 11H ), deuterium ( 1 2H or D) and tritium (11H or T ).The atomic number of each one is 1, but the mass number is 1, 2 and 3, respective. Other such examples are (1) Carbon 612C and 614C, (2) Chlorine, 1735Cl and 1737Cl, etc.
Many elements consist of a mixture of isotopes. Each isotopes of an element is a pure substance. The chemical properties of isotopes are similar but their physical properties are different. Chlorine occurs in nature in two isotopic forms, with masses 35u and 37u in the ratio of 3:1.
The mass of an atom of any natural element is taken as the average mass of all the naturally occuring atoms of that element. If an atom has no isotopes, then the mass of its atom would be the same as the sum of protons and neutrons in it, then we have to know the percentage of each isotopic form and then the average mass is calculated.
(35*75/100 +37*25/100)
= 105/4 + 37/4
= 142/4 = 35.5u
So, it will contain both isotopes of chlorine and the average mass is 35.5u.
APPLICATION: Chemical properties of all the isotopes of an element are the same, some of them are as follows:-
- An isotope of uranium is used as a fuel in nuclear reactions.
- An isotope of cobalt is used in the treatment of cancer.
- An isotope of iodine is used in the treatment of goitre.
Isobars
The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of nucleus is the same in the atoms of this pair of elements. Atoms of different atomic numbers, which have the same mass number, are known as isobars.
