An element has the electron configuration [Kr] 4d^10 5s^2 5p^3. Which of the following statements about this element is correct?
Show the answer and explanation
Correct answer
B. It has 5 valence electrons.
Principle or equation
The valence electrons are those in the outermost shell (highest principal quantum number). For this configuration, the outermost shell is n=5, containing 2 (5s) + 3 (5p) = 5 electrons.
Why this answer is correct
The configuration ends with 5s^2 5p^3, so the element is in period 5, group 15 (pnictogen). It has 5 valence electrons. It is not a transition metal because the 4d subshell is completely filled; transition metals have partially filled d subshells. It is in period 5, not 6. It is not a noble gas because the p subshell is not full.
Example
Phosphorus has [Ne] 3s^2 3p^3, with 5 valence electrons. Similarly, this element has 5 valence electrons.
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