Multiple Choice
Which statement best describes how electrons are organized in the electron cloud of an atom?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following represents the complete electron configuration of a neutral scandium (Sc) atom?
A
1s^2 2s^2 2p^6 3s^2 3p^6 3d^3
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^3
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^2
Verified step by step guidance1
Identify the atomic number of scandium (Sc), which tells you the total number of electrons in a neutral atom. Scandium has an atomic number of 21, so it has 21 electrons.
Recall the order in which electron orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
Write the electron configuration by filling orbitals in order until you reach 21 electrons: start with 1s^2 (2 electrons), then 2s^2 (2 electrons), 2p^6 (6 electrons), 3s^2 (2 electrons), 3p^6 (6 electrons), which sums to 18 electrons so far.
Next, fill the 4s orbital with 2 electrons (since 4s fills before 3d), bringing the total to 20 electrons, and then place the remaining 1 electron in the 3d orbital.
Combine all these to write the complete electron configuration for scandium: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1$.
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