Multiple Choice
Which of the following is the correct electron configuration for helium (He)?
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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^2 2s^3
C
1s^1 2s^2
D
1s^2 2s^2
Verified step by step guidance1
Step 1: Determine the atomic number of lithium (Li), which tells you 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 the lowest energy orbitals first. The order starts with 1s, then 2s, then 2p, and so on.
Step 3: Fill the electrons into the orbitals starting from the lowest energy level. The 1s orbital can hold up to 2 electrons, so place 2 electrons there first.
Step 4: Place the remaining electron in the next available orbital, which is the 2s orbital. Since lithium has only 3 electrons, the third electron goes into 2s.
Step 5: Write the electron configuration by indicating the number of electrons in each orbital: 1s has 2 electrons, and 2s has 1 electron, resulting in the configuration $1\mathrm{s}^2\ 2\mathrm{s}^1$.
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