Multiple Choice
What is the ground-state electron configuration of gallium (Ga, atomic number 31) using noble-gas shorthand?
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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 selenium (Se, ) using noble-gas shorthand?
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Verified step by step guidance1
Identify the atomic number (Z) of selenium, which is 34. This means selenium has 34 electrons to place in its electron configuration.
Start with the noble gas that precedes selenium in the periodic table to use as shorthand. The noble gas before selenium is argon (Ar), which has 18 electrons. So, begin the configuration with [Ar].
After [Ar], add the electrons in the 4s orbital. The 4s orbital can hold 2 electrons, so write 4s\^2.
Next, fill the 3d orbitals. The 3d subshell can hold 10 electrons, so add 3d\^10.
Finally, place the remaining electrons in the 4p orbitals. Since selenium has 34 electrons total, and 18 (Ar) + 2 (4s) + 10 (3d) = 30 electrons accounted for, the remaining 4 electrons go into 4p, written as 4p\^4.
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