Multiple Choice
Which noble gas is used as the core in the electron configuration of ruthenium (Ru)?
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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 barium (Ba)?
A
[Xe] 4f14 5d10 6s2
B
[Xe] 5d2
C
[Xe] 6s2
D
[Kr] 5s2 4d10 5p6 6s2
Verified step by step guidance1
Identify the atomic number of barium (Ba), which is 56. This tells us how many electrons need to be arranged in the electron configuration.
Recall the electron configuration of the noble gas preceding barium, which is xenon (Xe) with atomic number 54. Using the noble gas shorthand, start the configuration with [Xe].
Determine the orbitals that come after xenon to accommodate the remaining 2 electrons (since 56 - 54 = 2). These electrons will fill the 6s orbital next, according to the Aufbau principle.
Write the electron configuration after [Xe] by adding the electrons in the 6s orbital: [Xe] 6s2.
Verify that no electrons are added to the 4f or 5d orbitals for barium, as these orbitals start filling in elements with higher atomic numbers (lanthanides and transition metals).
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