Question

which is the electron configuration for lithium?
○ 1s²
○ 2s³
○ 1s²2s¹
○ 1s¹2s²

Explanation:

Lithium has an atomic number of 3, meaning it has 3 electrons. The electron configuration follows the Aufbau principle. The 1s orbital can hold up to 2 electrons, and the remaining 1 electron goes to the 2s orbital. So the electron configuration should be \(1s^2 2s^1\). Let's analyze the options:

• \(1s^2\): This has only 2 electrons, which is for helium, not lithium.
• \(2s^3\): The s - orbital can hold a maximum of 2 electrons, so this is invalid.
• \(1s^2 2s^1\): This has 2 + 1=3 electrons, which matches the number of electrons in lithium.
• \(1s^1 2s^2\): This has a total of 3 electrons, but the filling order is wrong. The 1s orbital should be filled before the 2s orbital, so 1s should have 2 electrons first.

Answer:

\(1s^2 2s^1\) (the third option: \(1s^2 2s^1\))