Multiple Choice
How many valence electrons does an oxygen atom have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Phosphorus has an atomic number of 15. How many valence electrons does a neutral phosphorus atom possess?
A
7
B
8
C
5
D
3
Verified step by step guidance1
Identify the atomic number of phosphorus, which is 15. This means a neutral phosphorus atom has 15 electrons.
Determine the electron configuration of phosphorus by filling the orbitals in order: 1s, 2s, 2p, 3s, and 3p.
Write the electron configuration: $1s^2 2s^2 2p^6 3s^2 3p^3$.
Recognize that valence electrons are the electrons in the outermost shell (highest principal quantum number). For phosphorus, this is the third shell (3s and 3p orbitals).
Count the electrons in the 3s and 3p orbitals: $3s^2$ has 2 electrons and $3p^3$ has 3 electrons, so total valence electrons = 2 + 3 = 5.
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