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Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
Answer
(i) Atomic number
- It is the number of protons present in the nucleus of an atom
- It is denoted by Z
Example - 1
- For Hydrogen, Z = 1
- It means that in a hydrogen atom, there are 1 proton present in the nucleus.
Example - 2
- For Carbon, Z = 6
It means that in a carbon atom, there are 6 protons in the nucleus.
ii) Mass number
- Mass number is the total number of protons and neutrons present in the nucleus of an atom.
- It is denoted by A .
Example - 1
- Carbon atom has 6 protons and 6 neutrons
- So, Mass number is 6 + 6 = 12
- A = 12
Example - 2
- An aluminium atom has 13 protons and 14 neutrons
- So, Mass number = 13 + 14 = 27
- A = 27
iii) Isotopes
- Isotopes are elements having the same atomic number but different mass numbers.
- That is, they’ve equal number of protons/electrons but different numbers of neutrons.
- Because they’ve same number of electrons, their electronic configuration is the same.
- Example, and .
- Atomic number of both the elements is 17 but mass numbers are different.
iv) Isobars
- Isobars are elements having different atomic numbers but same mass numbers.
- That is, they’ve same number of nucleons (protons+neutrons) but different numbers of protons/electrons.
- Because they’ve different numbers of electrons, their electronic configuration is different.
- For example, and .
- Mass number of both the elements is 40 but atomic numbers are different.
