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Question
State and explain Pauli’s exclusion principle.
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Solution
Pauli’s exclusion principle:
- Statement: “No two electrons in an atom can have the same set of four quantum numbers”. OR “Only two electrons can occupy the same orbital and they must have opposite spins.”
- The capacity of an orbital to accommodate electrons is decided by Pauli’s exclusion principle.
- According to this principle, for an electron belonging to the same orbital, the spin quantum number must be different since the other three quantum numbers are the same.
- The spin quantum number can have two values: `+1/2` and `-1/2`.
- For example, consider helium (He) atom with electronic configuration 1s2.
For the two electrons in 1s orbital, the four quantum numbers are as follows:
Thus, in an atom, any two electrons can have the same three quantum numbers, but the fourth quantum number must be different.Electron number Quantum number Set of values of quantum numbers n l m s 1st Electron 1 0 0 `+1/2` `(1,0,0,+1/2)` 2nd Electron 1 0 0 `-1/2` `(1,0,0,-1/2)` - This leads to the conclusion that an orbital can accommodate a maximum of two electrons and if it has two electrons, they must have opposite spin.
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