Multiple Choice
How many valence electrons does the element lithium (Li) have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which of the following represents the valence electron configuration for a calcium (Ca) atom?
A
4s^2
B
4p^2
C
3d^2
D
3s^2 3p^6
Verified step by step guidance1
Identify the atomic number of calcium (Ca), which is 20. This tells us that a neutral calcium atom has 20 electrons.
Recall the order in which electron orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.
Write the full electron configuration for calcium by filling orbitals in order until all 20 electrons are placed: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2.
Determine the valence electrons by identifying the electrons in the outermost shell. For calcium, the outermost shell is the 4th shell, which contains the 4s^2 electrons.
Conclude that the valence electron configuration for calcium is $4s^2$, since the 3d and 4p orbitals are either empty or belong to inner shells for this element.
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