Multiple Choice
Which of the following is the correct electron configuration for calcium (atomic number 20)?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following represents the electron configuration for the valence electrons in a chlorine atom?
A
3s^2 3p^6
B
2s^2 2p^5
C
4s^2 4p^5
D
3s^2 3p^5
Verified step by step guidance1
Identify the atomic number of chlorine, which is 17. This means a chlorine atom has 17 electrons in total.
Recall that valence electrons are the electrons in the outermost shell (highest principal quantum number, n) of an atom.
Determine the electron configuration of chlorine by filling orbitals in order: 1s, 2s, 2p, 3s, and 3p, until all 17 electrons are placed.
Recognize that the valence shell for chlorine is the third shell (n=3), so the valence electrons are those in the 3s and 3p orbitals.
Write the valence electron configuration by combining the electrons in the 3s and 3p orbitals, which results in $3s^2 3p^5$.
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