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What are Nucleons?
- We know that every atom contains protons, neutrons and electrons
- Out of this, Protons and Neutrons are present in the nucleus of an atom.
- They are together called Nucleons .
What is an atomic number?
- It is the number of protons present in the nucleus of an atom .
- It is denoted by Z .
Example - 1
- For Hydrogen, Atomic number (Z) = 1
- It means that in a hydrogen atom, there are 1 proton present in the nucleus.
Example - 2
- For Carbon, Atomic Number (Z) = 6
It means that in a carbon atom, there are 6 protons in the nucleus.
What is 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
- Mass number (A) = 12
Example - 2
- An aluminium atom has 13 protons and 14 neutrons
- So, Mass number = 13 + 14 = 27
- Mass number (A) = 27
How is Atomic and Mass Number Represented?
- Atomic Number is represented as Subscript
- Mass Number is represented as Superscript
Example
- Nitrogen has 7 Protons and 7 Neutrons
- Hence Atomic Number = Z = No of Protons = 7
Mass Number = A = Number of Protons + Number of Neutrons = 7 + 7 = 14
Examples -
In text Question -
NCERT Back Exercise - Q8 (i) (ii), Q19
