An element has the electron configuration [Ar] 3d^5 4s^1. Which of the following statements about this element is correct?
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Correct answer
C. It is a transition metal with 1 valence electron.
Principle or equation
The electron configuration determines the block and group. For transition metals, the valence electrons are typically the s electrons in the highest principal energy level, while d electrons are inner-shell. The element with [Ar] 3d^5 4s^1 is chromium (Cr), a transition metal in group 6, with one 4s electron.
Why this answer is correct
The configuration [Ar] 3d^5 4s^1 indicates that the 4s subshell is partially filled (1 electron) and the 3d subshell has 5 electrons. Elements with partially filled d orbitals are transition metals. The valence electrons are those in the highest energy level (n=4), which is only the 4s^1 electron. Thus, it has 1 valence electron.
Example
For [Ar] 3d^10 4s^1 (copper), the valence electron is the 4s^1 electron, making it a transition metal with 1 valence electron.
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