To determine the correct electron configuration for lithium (Li) with an atomic number of 3, we need to distribute the three electrons across the available atomic orbitals following the principles of quantum mechanics and electron configuration rules.
1. Identify the total number of electrons: Lithium has an atomic number of 3, which means it has 3 electrons.
2. Distribute electrons according to the Aufbau principle:
- The Aufbau principle states that electrons fill atomic orbitals in order of increasing energy levels. The order is generally: 1s, 2s, 2p, 3s, 3p, etc.
3. Fill the 1s orbital first:
- The 1s orbital can hold a maximum of 2 electrons.
- Place the first 2 electrons in the 1s orbital: [tex]\( 1s^2 \)[/tex]
4. Move to the next available orbital, 2s:
- After filling the 1s orbital, we have 1 electron left.
- Place this remaining 1 electron in the 2s orbital: [tex]\( 2s^1 \)[/tex]
By following the electron configuration rules, the electrons are arranged as follows:
[tex]\[ 1s^2 2s^1 \][/tex]
5. Verify against the given options:
- Option 1: [tex]\( 1s^2 \)[/tex]
- Option 2: [tex]\( 2s^3 \)[/tex] (This configuration is not possible since the 2s orbital can hold a maximum of 2 electrons.)
- Option 3: [tex]\( 1s^2 2s^1 \)[/tex] (This matches our derived configuration.)
- Option 4: [tex]\( 1s^1 2s^2 \)[/tex] (This configuration does not match the distribution for lithium.)
Therefore, the correct electron configuration for lithium is:
[tex]\[ 1s^2 2s^1 \][/tex]
And the correct answer from the given options is:
[tex]\[ \boxed{1s^2 2s^1} \][/tex]
