Multiple Choice
Which element has the following ground state electron configuration: 1s^2 2s^2 2p^6 3s^2 3p^4?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the correct electron configuration for the Co^{2+} ion?
A
[Ar] 3d^6
B
[Ar] 3d^7
C
[Ar] 3d^5 4s^2
D
[Ar] 3d^6 4s^1
Verified step by step guidance1
Step 1: Determine the atomic number of cobalt (Co). Cobalt has an atomic number of 27, which means a neutral cobalt atom has 27 electrons.
Step 2: Write the electron configuration for the neutral cobalt atom. The full configuration is $1s^2 2s^2 2p^6 3s^2 3p^6 3d^7 4s^2$, which can be abbreviated as $[Ar] 3d^7 4s^2$.
Step 3: Understand that when forming the $Co^{2+}$ ion, two electrons are removed from the neutral atom. Electrons are removed first from the outermost shell, which is the 4s orbital before the 3d orbitals.
Step 4: Remove two electrons from the $4s$ orbital of the neutral cobalt configuration $[Ar] 3d^7 4s^2$. This results in the configuration $[Ar] 3d^7$ for $Co^{2+}$.
Step 5: Compare the given options with the derived configuration $[Ar] 3d^7$ to identify the correct electron configuration for the $Co^{2+}$ ion.
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