Multiple Choice
Which of the following is the best method to determine the number of valence electrons for a main-group element using the periodic table?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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How many unpaired electrons are present in a ground-state phosphorus (P) atom?
A
5
B
0
C
1
D
3
Verified step by step guidance1
Identify the atomic number of phosphorus (P), which is 15. This means a neutral phosphorus atom has 15 electrons.
Write the electron configuration for phosphorus in its ground state. The order of filling orbitals is 1s, 2s, 2p, 3s, and then 3p. So, the configuration is $1s^2 2s^2 2p^6 3s^2 3p^3$.
Focus on the outermost electrons, which are in the 3p subshell. The 3p subshell can hold up to 6 electrons, but phosphorus has 3 electrons in this subshell.
Apply Hund's rule to the 3p subshell: electrons will occupy separate orbitals singly before pairing up. Since there are 3 electrons, each will occupy its own 3p orbital, resulting in 3 unpaired electrons.
Conclude that the number of unpaired electrons in a ground-state phosphorus atom is 3.
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