Multiple Choice
Which of the following statements summarizing valence bond theory is correct?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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How many valence electrons does an iron atom (Fe) have?
A
6
B
8
C
2
D
4
Verified step by step guidance1
Identify the electron configuration of an iron (Fe) atom. Iron has an atomic number of 26, so it has 26 electrons. Write the electron configuration using the Aufbau principle: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6$.
Recall that valence electrons are the electrons in the outermost shell (highest principal quantum number, n) that participate in bonding. For transition metals like iron, valence electrons include the electrons in the outermost s orbital and the d orbitals of the penultimate shell.
Determine the outermost shell for iron. The 4s orbital (n=4) is the outermost shell, and it contains 2 electrons. The 3d orbitals (n=3) are also considered valence electrons for transition metals because they are involved in bonding.
Count the valence electrons by adding the electrons in the 4s and 3d orbitals: $4s^2$ and $3d^6$ gives a total of 8 valence electrons.
Understand that in some contexts, especially in simple bonding models, only the 4s electrons are counted as valence electrons for iron, which is why the answer might be 2. Clarify the context of the question to decide which counting method applies.
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