Isotopes are the different forms of the same element, which have the same atomic number but different mass numbers.
Name |
Symbol |
Atomic number |
Mass number |
Relative abundance |
Nature radioactive or non-radioactive |
Protium or Hydrogen |
11H or H |
1 |
1 |
99.985% |
Non-radioactive |
Deuterium |
21H or D |
1 |
2 |
0.015% |
Non-radioactive |
Tritium |
31H or T |
1 |
3 |
10–15% |
Radioactive |
Physical constants of H2 , D2 and T2
Property |
H2 |
D2 |
T2 |
Molecular mass |
2.016 |
4.028 |
6.03 |
Melting point (K) |
13.8 |
18.7 |
20.63 |
Boiling point (K) |
20.4 |
23.9 |
25.0 |
Heat of fusion (kJ mol–1)
|
0.117 |
0.197 |
0.250 |
Heat of vaporisation (kJ mol–1)
|
0.994 |
1.126 |
1.393 |
Bond energy (kJ mol–1)
|
435.9 |
443.4 |
446.9 |
Isotopic effect : In general chemical properties of isotopes are same but quantiative differences are noticed amongst them. For example, the reaction between H2
and Cl2
is 13.4 times faster between D2
and Cl2
under similar conditions. Such differences in chemical properties, which are due to difference in the mass numbers of isotopes is known as isotopic effect. |
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