The 3rd electron shell can hold either 8 or 18 electrons, depending on whether you are considering just the lower energy s and p orbitals, or also including the higher energy d orbitals.
Explanation:
Electron shells represent the energy levels of electrons in an atom. Each shell can hold a specific number of electrons. This capacity is determined by the number of orbitals within each shell. Each orbital can hold up to 2 electrons.
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Principal Quantum Number (n): The third shell corresponds to n=3.
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Orbitals in the 3rd Shell: The third shell contains the following orbitals:
- One s orbital (3s) which can hold up to 2 electrons.
- Three p orbitals (3p) which can hold up to 6 electrons.
- Five d orbitals (3d) which can hold up to 10 electrons.
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Electron Capacity:
- If we only consider the 3s and 3p orbitals, the third shell can hold 2 + 6 = 8 electrons. This is the configuration seen in elements like Argon (Ar) when filling orbitals according to the Aufbau principle.
- If we include the 3d orbitals, the third shell can hold 2 + 6 + 10 = 18 electrons.
In summary:
- The third shell, in its lowest energy state, typically holds 8 electrons (following the octet rule for many elements).
- The full capacity of the third shell, including the d orbitals, is 18 electrons.
This means the context of the question is critical to answering properly. If talking about electron configuration in the early periodic table, 8 is often a more useful answer. When discussing transition metals and larger atoms, 18 is more useful.
