Multiple Choice
Which of the following represents the correct electron configuration for a neutral oxygen 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^5 5s^2
B
[Kr] 4d^6 5s^1
C
[Kr] 4d^5 5s^2 5p^1
D
[Kr] 4d^5 5s^2
Verified step by step guidance1
Step 1: Identify the atomic number of technetium (Tc), which is 43. This means Tc has 43 electrons to be placed in orbitals according to the Aufbau principle.
Step 2: Write the electron configuration of the noble gas preceding technetium, which is krypton (Kr), with atomic number 36. This serves as the core configuration: $[\mathrm{Kr}]$.
Step 3: After krypton, electrons fill the 5s and 4d orbitals. According to the Aufbau principle, the 5s orbital fills before the 4d orbitals. So, place 2 electrons in 5s: $5s^2$.
Step 4: Distribute the remaining electrons (43 - 36 - 2 = 5) into the 4d orbitals. The 4d subshell can hold up to 10 electrons, so place 5 electrons as $4d^5$.
Step 5: Combine the core and valence electrons to write the full electron configuration: $[\mathrm{Kr}] 4d^5 5s^2$. Check that the total number of electrons sums to 43 and that the configuration follows the Aufbau principle and Hund's rule.
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