Which electron configuration correctly represents a neutral lithium atom (atomic number 3) in its ground state?

• A. $1s^{2}2p^1$
• B. $1s^{2}2s^1$
• C. $1s^{1}2s^2$
• D. $1s^{2}2s^2$

Answer: (B)

Verified step by step guidance

1. Identify the atomic number of lithium, which is 3. This means a neutral lithium atom has 3 electrons.
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.
3. Fill the 1s orbital first, which can hold up to 2 electrons. Since lithium has 3 electrons, 2 will go into the 1s orbital.
4. Place the remaining 1 electron in the next available lowest energy orbital, which is the 2s orbital.
5. Write the electron configuration by showing the number of electrons in each orbital: \$1\text{s}^2 2\text{s}^1$.