Multiple Choice
How many valence electrons does cesium (Cs) have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which of the following represents the valence electron configuration for a phosphorus (P) atom?
A
3s^2 3p^5
B
4s^2 4p^3
C
3s^2 3p^3
D
2s^2 2p^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.
Determine the electron configuration by filling orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, etc., until all 15 electrons are placed.
Recognize that the valence electrons are those in the outermost shell, which for phosphorus is the third shell (n=3).
Write the valence electron configuration by noting the electrons in the 3s and 3p orbitals after filling the lower energy orbitals completely.
Compare the valence electron configurations given in the options to the correct valence configuration for phosphorus, which should be $3s^2 3p^3$.
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