Multiple Choice
Which of the following is a requirement for an atom to have an expanded valence shell (expanded octet)?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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How many valence electrons does a copper (Cu) atom have?
A
1
B
2
C
10
D
8
Verified step by step guidance1
Identify the electron configuration of a neutral copper (Cu) atom. Copper has an atomic number of 29, so it has 29 electrons.
Write the electron configuration for copper: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^{10}$.
Recall that valence electrons are the electrons in the outermost shell (highest principal quantum number, n). For copper, the outermost shell is the 4th shell, which contains the $4s^1$ electron.
Note that the $3d^{10}$ electrons are in the third shell and are considered part of the transition metal's d-subshell, which can sometimes contribute to valence behavior, but typically only the $4s$ electron is counted as valence for copper.
Conclude that copper has 1 valence electron, corresponding to the single electron in the $4s$ orbital.
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