To determine the correct electron configuration for lithium, we need to remember that lithium has an atomic number [tex]\( Z = 3 \)[/tex], meaning it has 3 electrons. Electron configurations describe the arrangements of electrons in atomic orbitals, and we fill these orbitals following specific rules, including the Aufbau principle, Pauli exclusion principle, and Hund's rule.
1. Aufbau Principle: Electrons occupy orbitals starting from the lowest energy level.
2. Pauli Exclusion Principle: Each orbital can hold a maximum of 2 electrons with opposite spins.
3. Hund's Rule: When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with parallel spins.
We will fill the orbitals for lithium step by step:
1. First 2 electrons: The lowest energy orbital is the 1s orbital. According to the Aufbau principle, the first two electrons go into the 1s orbital:
[tex]\[
1s^2
\][/tex]
2. Next electron: After filling the 1s orbital, we move to the next lowest energy level, which is the 2s orbital. Since lithium has only one more electron to place, it goes into the 2s orbital:
[tex]\[
2s^1
\][/tex]
So, combining these, the electron configuration for lithium is:
[tex]\[
1s^2 2s^1
\][/tex]
Let's consider the options provided:
- [tex]\(1s^2\)[/tex]: This configuration is incomplete for lithium as it accounts for only 2 electrons.
- [tex]\(2s^3\)[/tex]: This configuration is not possible because the 2s orbital can only hold a maximum of 2 electrons.
- [tex]\(1s^2 2s^1\)[/tex]: This configuration correctly accounts for all 3 electrons of lithium.
- [tex]\(1s^1 2s^2\)[/tex]: This configuration incorrectly places 2 electrons in the 2s orbital before fully occupying the 1s orbital.
Therefore, the correct electron configuration for lithium is:
\[
1s^2 2s^1
\
