To determine the electron configuration for lithium, we need to understand the distribution of electrons in an atom. Lithium has an atomic number of 3, which means it has 3 electrons.
The electron configuration of atoms follows a specific order dictated by the Aufbau principle, Hund's rule, and the Pauli exclusion principle. Electrons fill orbitals starting from the lowest energy level to higher energy levels.
1. Energy levels and sublevels: The first energy level (n=1) has only one sublevel, which is the 1s orbital, and can hold a maximum of 2 electrons:
[tex]\[
1s^2
\][/tex]
2. Filling the next energy level: After filling the 1s orbital, we move on to the second energy level (n=2), which starts filling with the 2s orbital. The 2s orbital can also hold a maximum of 2 electrons, but since we only have one electron left after filling 1s, it goes into the 2s orbital:
[tex]\[
2s^1
\][/tex]
Combining these, the electron configuration for lithium is:
[tex]\[
1s^2 2s^1
\][/tex]
Given the options, the correct electron configuration for lithium is:
[tex]\[
\textbf{3. } \ 1s^2 2s^1
\][/tex]
Thus, the correct electron configuration for lithium is option 3: [tex]\( 1s^2 2s^1 \)[/tex].
