Multiple Choice
Which of the following is the correct electron configuration for arsenic (As)?
10. Periodic Properties of the Elements
The Electron Configuration
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What is the ground state electron configuration of a calcium ion (Ca²⁺)?
A
[Ar]
B
[Ar] 3d²
C
[Ar] 4s²
D
[Ne] 3s² 3p⁶
Verified step by step guidance1
Identify the atomic number of calcium (Ca), which is 20. This means a neutral calcium atom has 20 electrons.
Write the electron configuration for a neutral calcium atom. The configuration is: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².
Recognize that a calcium ion (Ca²⁺) has lost 2 electrons compared to the neutral atom. This means we need to remove 2 electrons from the outermost shell.
Remove the 2 electrons from the 4s orbital, as they are the outermost electrons in the neutral calcium atom. This leaves us with the electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶.
Notice that the remaining electron configuration is the same as that of the noble gas argon (Ar), which is [Ar]. Therefore, the ground state electron configuration of Ca²⁺ is [Ar].
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