Multiple Choice
Which atomic symbol represents the noble gas with 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 magnesium (atomic number 12)?
A
1s^2 2s^2 2p^6 3s^1 3p^1
B
1s^2 2s^2 2p^6 3d^2
C
1s^2 2s^2 2p^6 3p^2
D
1s^2 2s^2 2p^6 3s^2
Verified step by step guidance1
Step 1: Identify the atomic number of magnesium, which is 12. This means magnesium has 12 electrons to place in its electron configuration.
Step 2: Recall the order in which electron orbitals are filled according to the Aufbau principle: $1s$, $2s$, $2p$, $3s$, $3p$, $4s$, $3d$, etc.
Step 3: Begin filling the orbitals with electrons, starting from the lowest energy level: fill $1s$ with 2 electrons, $2s$ with 2 electrons, and $2p$ with 6 electrons. This accounts for 10 electrons so far.
Step 4: Place the remaining 2 electrons in the next available orbital, which is $3s$. So, $3s$ will have 2 electrons.
Step 5: Write the full electron configuration for magnesium as $1s^2 2s^2 2p^6 3s^2$, confirming that this matches the total of 12 electrons and follows the correct filling order.
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