An orbital can hold a maximum of two electrons.
This is a fundamental principle in chemistry and quantum mechanics. Let's break down why:
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Quantum Numbers and Orbitals: Each electron within an atom is described by a unique set of four quantum numbers. These numbers define the electron's energy level, shape of its orbital, spatial orientation, and spin.
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Pauli Exclusion Principle: The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of all four quantum numbers.
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Spin Quantum Number: For a given orbital (defined by the first three quantum numbers), there are only two possible values for the spin quantum number: +1/2 and -1/2. These are often referred to as "spin up" and "spin down."
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Implication: Since only the spin quantum number can differ for electrons occupying the same orbital, a maximum of two electrons, with opposite spins, can occupy any single orbital.
Examples:
- An s subshell has one orbital, so it can hold a maximum of 2 electrons.
- A p subshell has three orbitals, so it can hold a maximum of 6 electrons (2 electrons per orbital x 3 orbitals).
- A d subshell has five orbitals, so it can hold a maximum of 10 electrons.
- An f subshell has seven orbitals, so it can hold a maximum of 14 electrons.
| Subshell | Number of Orbitals | Maximum Number of Electrons |
|---|---|---|
| s | 1 | 2 |
| p | 3 | 6 |
| d | 5 | 10 |
| f | 7 | 14 |
In summary, the maximum number of electrons that can occupy a single atomic orbital is two, due to the Pauli Exclusion Principle and the two possible spin states for an electron.
