Multiple Choice
Which of the following is the correct electron configuration for a neutral sulfur atom?
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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 technetium (Tc, atomic number 43)?
A
[Kr] 4d^6 5s^1
B
[Kr] 4d^5 5s^2
C
[Kr] 4d^5 5s^2
D
[Kr] 4d^5 5s^2 5p^1
Verified step by step guidance1
Identify the atomic number of technetium (Tc), which is 43. This means Tc has 43 electrons to be arranged in its electron configuration.
Recall the electron configuration of the noble gas preceding technetium, which is krypton (Kr) with atomic number 36. This serves as the core configuration: $[\mathrm{Kr}]$.
Determine the order in which electrons fill the orbitals beyond krypton. The 5s orbital fills before the 4d orbitals, so electrons will fill 5s first, then 4d.
Distribute the remaining 7 electrons (43 - 36 = 7) into the 5s and 4d orbitals following the Aufbau principle, Hund's rule, and the Pauli exclusion principle. This means filling 5s with up to 2 electrons and then placing the rest in 4d orbitals.
Compare the given options with the expected electron configuration based on these rules. The correct configuration will have 2 electrons in 5s and 5 electrons in 4d, written as $[\mathrm{Kr}] 4d^{5} 5s^{2}$.
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