Multiple Choice
Which of the following best describes valence electrons and explains their significance in chemistry?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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How many valence electrons are present in the ground-state electron configuration of a nitrogen atom?
A
5
B
2
C
3
D
7
Verified step by step guidance1
Identify the atomic number of nitrogen, which is 7. This means a nitrogen atom has 7 electrons in total.
Write the ground-state electron configuration of nitrogen by filling the orbitals in order of increasing energy: 1s, 2s, then 2p. The configuration is $1s^2 2s^2 2p^3$.
Recall that valence electrons are the electrons in the outermost shell (highest principal quantum number, n). For nitrogen, the outermost shell is the second shell (n=2).
Count the electrons in the 2s and 2p orbitals: $2s^2$ has 2 electrons and $2p^3$ has 3 electrons, so total valence electrons = 2 + 3.
Conclude that the number of valence electrons in nitrogen is the sum of electrons in the 2s and 2p orbitals.
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