Multiple Choice
When an electron transitions from a higher energy level to a lower energy level in an atom, which of the following occurs?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the correct electron configuration for a neutral lithium (Li) atom?
A
1s^2 2s^1
B
1s^1 2s^2
C
1s^2 2p^1
D
1s^2 2s^3
Verified step by step guidance1
Step 1: Determine the atomic number of lithium (Li), which tells us the number of electrons in a neutral atom. Lithium has an atomic number of 3, so it has 3 electrons.
Step 2: Recall the order in which electron orbitals are filled according to the Aufbau principle: electrons fill orbitals starting from the lowest energy level to higher ones. The order begins with 1s, then 2s, then 2p, and so on.
Step 3: Fill the electrons into the orbitals following the Pauli exclusion principle and Hund's rule. The 1s orbital can hold up to 2 electrons, so place 2 electrons there first.
Step 4: Place the remaining 1 electron in the next available lowest energy orbital, which is the 2s orbital.
Step 5: Write the electron configuration by listing the orbitals and the number of electrons in each, resulting in $1s^{2} 2s^{1}$ for a neutral lithium atom.
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