Multiple Choice
Which of the following is the correct number of valence electrons in the element gallium (Ga)?
10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which electrons are considered valence electrons in the electron configuration of cobalt (Co)?
A
Only the 3d electrons
B
Only the 4s electrons
C
The 4s and 3d electrons
D
The 3p and 4s electrons
Verified step by step guidance1
Recall that valence electrons are the electrons in the outermost shell of an atom that are involved in chemical bonding and reactions.
Write the electron configuration of cobalt (Co), which has an atomic number of 27. The configuration is: $1s^2 2s^2 2p^6 3s^2 3p^6 3d^7 4s^2$.
Identify the highest principal energy level (n) in the configuration. For cobalt, the highest n is 4, which corresponds to the 4s electrons.
Recognize that transition metals like cobalt also use their (n-1)d electrons as valence electrons because these electrons participate in bonding and chemical behavior.
Conclude that both the 4s electrons (from the highest energy level) and the 3d electrons (from the penultimate shell) are considered valence electrons in cobalt.
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