Multiple Choice
Which one of the following species has the electron configuration 1s^2 2s^2 2p^6?
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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 gallium (Ga)?
A
1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^1
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^1
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 4p^1 3d^{10}
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^9 4p^2
Verified step by step guidance1
Identify the atomic number of gallium (Ga), which is 31. This tells us the total number of electrons to place in the electron configuration.
Recall the order of filling orbitals according to the Aufbau principle, which generally follows the sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.
Fill the orbitals in order, making sure to add electrons to each subshell until the total number of electrons equals 31. Remember that 4s fills before 3d because it is lower in energy.
Write the electron configuration by listing the orbitals in the order of increasing energy, with the correct number of electrons in each subshell, using the notation $n\ell^{x}$ where $n$ is the principal quantum number, $\ell$ is the subshell type (s, p, d), and $x$ is the number of electrons.
Compare the given options to the correct order and electron count, noting that the 4s subshell is filled before the 3d subshell, so the correct configuration places $4s^2$ before $3d^{10}$ and then $4p^1$.
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