Question

Name the atoms of a substance having same atomic number, but different mass numbers. Give one example of such a substance. How do the structures of such atoms differ?

1. What is the name given to atoms of a substance which have the same atomic number, but different mass number?
2. What is the difference in the atomic structure of such atoms?

Answer 1

Atoms of a substance having the same atomic number, but different mass numbers, are called isotopes.

Example: Hydrogen has three isotopes

1. Protium \[\ce{^1_1H}\]
2. deuterium \[\ce{^2_1H}\]
3. tritium \[\ce{^3_1H}\]

Difference in structure:

Parameter	Protium \[\ce{^1_1H}\]	Deuterium \[\ce{^2_1H}\]	Tritium \[\ce{^3_1H}\]
Value of Z and A	Z = 1; A =2	Z = 1, A = 3	Z = 1, A = 1
No. of protons	1	1	1
no. of neutrons	0	1	2
no. of electrons	1	1	1