Multiple Choice
Which is the correct ground-state electron configuration for phosphorus (P), atomic number 15?
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9. Electrons in Atoms and the Periodic Table
The Electron Configuration (Simplified)
Multiple Choice
What is the ground-state electron configuration of krypton (Kr) in noble-gas shorthand notation?
A
[Ne]
B
[Ar]
C
[Ar]
D
[Ar]
Verified step by step guidance1
Identify the atomic number of krypton (Kr), which is 36. This tells us krypton has 36 electrons in its neutral ground state.
Recall that noble-gas shorthand notation uses the electron configuration of the previous noble gas as a starting point. The noble gas before krypton is argon (Ar), with atomic number 18.
Write the electron configuration starting with [Ar], which accounts for the first 18 electrons. Then, add the electrons that come after argon to reach 36 electrons total.
Fill the orbitals in order of increasing energy: after [Ar], electrons fill the 4s orbital (2 electrons), then the 3d orbital (10 electrons), and finally the 4p orbital (6 electrons) to complete krypton's configuration.
Combine these to write the full noble-gas shorthand electron configuration for krypton as \([\mathrm{Ar}]\,4s^{2}\,3d^{10}\,4p^{6}\).
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