Multiple Choice
Which set of four quantum numbers represents the last electron added to the Zn atom according to the Aufbau principle?
9. Quantum Mechanics
Quantum Numbers: Principal Quantum Number
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How many electrons are in the n = 3 shell of a magnesium ion (Mg²⁺)?
A
8
B
0
C
2
D
6
Verified step by step guidance1
Understand the electron configuration of a neutral magnesium atom. Magnesium (Mg) has an atomic number of 12, meaning it has 12 electrons in its neutral state. The electron configuration is: 1s² 2s² 2p⁶ 3s².
Identify the electron configuration of the magnesium ion (Mg²⁺). When magnesium forms a Mg²⁺ ion, it loses two electrons. These electrons are removed from the outermost shell, which is the 3s orbital.
Determine the electron configuration of Mg²⁺ after losing two electrons. The configuration becomes: 1s² 2s² 2p⁶.
Recognize that the n = 3 shell corresponds to the third energy level, which includes the 3s and 3p orbitals. Since Mg²⁺ has lost its 3s electrons, there are no electrons left in the n = 3 shell.
Conclude that the number of electrons in the n = 3 shell of a Mg²⁺ ion is 0, as all electrons in this shell have been removed to form the ion.
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