Multiple Choice
Which of the following is the correct electron configuration for strontium (Sr, atomic number 38)?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the correct abbreviated electron configuration for nickel (atomic number 28)?
A
[Ar] 4s2 3d8
B
[Ne] 3s2 3p6 4s2 3d8
C
[Kr] 4d10 5s2
D
[Ar] 4s1 3d9
Verified step by step guidance1
Identify the atomic number of nickel, which is 28. This tells us nickel has 28 electrons to place in orbitals according to the Aufbau principle.
Recall the electron configuration order: electrons fill orbitals starting from the lowest energy level to higher ones, typically following the sequence 1s, 2s, 2p, 3s, 3p, 4s, 3d, and so on.
Determine the noble gas preceding nickel to use as the abbreviated core. The noble gas before nickel (Z=28) is argon (Ar), which has 18 electrons. So, the abbreviated configuration starts with [Ar].
Distribute the remaining electrons (28 - 18 = 10) into the 4s and 3d orbitals. According to the Aufbau principle, 4s fills before 3d, so place 2 electrons in 4s and the remaining 8 electrons in 3d.
Write the abbreviated electron configuration as $[\mathrm{Ar}]\ 4s^{2}\ 3d^{8}$, which matches the correct answer.
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