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Earlier scientists only believed that atom contained only positively charged protons and negatively charged electron
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Later in 1932
J.Chadwick
found out that there was another subatomic particle, this had
mass nearly equal to proton (1u)
however, it
did not have any charge
.
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This was later known as
Neutron
.
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This Neutron was
present in the nucleus of the atom along with protons
.
- Hence, the mass of a nucleus is given as a sum of mass of protons and mass of neutrons.
Note: Both protons and neutrons are present in the nucleus .
Hence, they are collectively called nucleons .
A neutron is represented by ‘ n ’.
Neutrons are present in the nucleus of all atoms except Hydrogen .
|
Protons |
Electrons |
Neutrons |
|
Protons are positively charged. |
Electrons are negatively charged. |
Neutrons do not have any charge. |
|
Atomic mass is 1u. |
Negligible atomic mass. |
Atomic mass is 1u . |
|
Located inside the nucleus. |
Located outside the nucleus in orbits/shells . |
Located inside the nucleus. |
|
Charge of a proton is +1 |
Charge of an electron is -1 |
Charge of a neutron is 0 |
Examples -
In text Question - Page 49 Q1, Q2
NCERT Back Exercise - Q1, 14(ii)
