Multiple Choice
How many valence electrons does argon (Ar) have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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For a sodium atom (Na), in which principal energy level are the valence electron(s) found?
A
n = 3
B
n = 1
C
n = 2
D
n = 4
Verified step by step guidance1
Recall that the principal energy level, denoted by the quantum number $n$, corresponds to the main shell or energy level where electrons reside around the nucleus.
Determine the electron configuration of a sodium atom (Na), which has an atomic number of 11, meaning it has 11 electrons.
Write the electron configuration by filling orbitals in order of increasing energy: $1s^2$, $2s^2$, $2p^6$, and then $3s^1$.
Identify the valence electrons as those in the outermost principal energy level, which is the highest $n$ value occupied by electrons.
Since the last electron enters the $3s$ orbital, the valence electron(s) of sodium are found in the principal energy level $n = 3$.
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