Multiple Choice
Which of the following elements has the electron configuration 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5?
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10. Periodic Properties of the Elements
The Electron Configuration
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How many electrons are present in the second energy level (n = 2) of a neutral lithium atom?
A
2
B
1
C
3
D
0
Verified step by step guidance1
Identify the atomic number of lithium, which tells us the total number of electrons in a neutral lithium atom. Lithium has an atomic number of 3, so it has 3 electrons.
Recall the order in which electrons fill energy levels (shells). The first energy level (n = 1) can hold up to 2 electrons, and the second energy level (n = 2) can hold up to 8 electrons.
Fill the first energy level (n = 1) with electrons first, since electrons occupy the lowest energy levels available. For lithium, place 2 electrons in the first energy level.
Subtract the electrons in the first energy level from the total number of electrons to find how many remain for the second energy level: 3 (total electrons) - 2 (in n=1) = 1 electron.
Conclude that the number of electrons in the second energy level (n = 2) of a neutral lithium atom is 1.
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