Chemistry

Structure of the Atom

1. Isotopes of Hydrogen.

The hydrogen element has three isotopes having the same atomic number of 1 but different mass numbers of 1, 2 and 3 respectively. The three isotopes of hydrogen can be represented as :

A = \begin{matrix} 1 \\ 1 \end{matrix}

A = \begin{matrix} 2 \\ 1 \end{matrix}

H and

A = \begin{matrix} 3 \\ 1 \end{matrix}

H
The three isotopes of hydrogen, ]H, ?H and have been given the special names of protium, deuterium and tritium respectively.
(i) Protium is the ordinary hydrogen isotope of mass number 1. Protium is represented as

A = \begin{matrix} 1 \\ 1 \end{matrix}

H .Protium does not have a special symbol.
(ii) Deuterium is the heavy hydrogen isotope of mass number 2.Deuterium is represented as

A = \begin{matrix} 2 \\ 1 \end{matrix}

H.The special symbol of deuterium is D.
(iii) Tritium is the very heavy hydrogen isotope of mass number 3.Tritium is represented as

A = \begin{matrix} 3 \\ 1 \end{matrix}

H.The special symbol of tritium is T.
Thus,we can now say that hydrogen element has three isotopes :protium,deuterium and tritium,having the same atomic number of 1 but different mass numbers of 1, 2 and 3 respectively.
The complete composition of the three isotopes of hydrogen is given below :

Name	Isotope	Protons	Neutrons	Electrons
Protium Deuterium Tritium	$A = \begin{matrix} 1 \\ 1 \end{matrix}$ H $A = \begin{matrix} 2 \\ 1 \end{matrix}$ H $A = \begin{matrix} 3 \\ 1 \end{matrix}$ H	1 1 1	0 1 2	1 1 1

It is clear from the above table that all the isotopes of hydrogen contain 1 proton and 1 electron each but they contain 0,1 and 2 neutrons respectively. Please note that the ordinary hydrogen isotope (protium) does not contain any neutron ; the heavy hydrogen isotope (deuterium) contains 1 neutron ; whereas the very heavy hydrogen isotope (tritium) contains 2 neutrons.
The diagrams of the three isotopes of hydrogen are given below :

Notes

Structure of the Atom - Notes

1. Drawback of Rutherford’s Model of the Atom