Multiple Choice
How many unpaired electrons are present in a ground state atom 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 a neutral phosphorus (P) atom?
A
1s^2 2s^2 2p^6 3s^2 3p^3
B
1s^2 2s^2 2p^6 3s^2 3p^5
C
1s^2 2s^2 2p^6 3s^2 3p^1
D
1s^2 2s^2 2p^6 3s^2 3p^6
Verified step by step guidance1
Step 1: Determine the atomic number of phosphorus (P), which tells you the number of electrons in a neutral atom. Phosphorus has an atomic number of 15, so it has 15 electrons.
Step 2: Recall the order in which electron orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, and so on.
Step 3: Fill the orbitals with electrons following the maximum capacity of each: 1s can hold 2 electrons, 2s can hold 2, 2p can hold 6, 3s can hold 2, and 3p can hold 6.
Step 4: Assign the 15 electrons to the orbitals in order: 2 electrons in 1s, 2 in 2s, 6 in 2p, 2 in 3s, and the remaining 3 electrons in 3p.
Step 5: Write the electron configuration using the notation $1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{3}$, which matches the distribution of all 15 electrons in phosphorus.
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