Since sodium (Na) is in period three of the periodic table, which of the following statements is correct about its electron configuration?

• A. It has a completely filled 3p subshell.
• B. Its highest energy electrons are in the 2p orbital.
• C. It has two valence electrons.
• D. Its valence electrons are in the 3s orbital.

Answer: (D)

Verified step by step guidance

1. Identify the atomic number of sodium (Na), which is 11, meaning it has 11 electrons to arrange in its electron configuration.
2. Recall the order of filling orbitals according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, etc.
3. Write the electron configuration for sodium by filling orbitals in order until all 11 electrons are placed: 1s² 2s² 2p⁶ 3s¹.
4. Note that the highest energy electron for sodium is in the 3s orbital, not in the 2p or 3p orbitals, and the 3p subshell is empty.
5. Recognize that the valence electrons are those in the outermost shell, which for sodium is the 3s orbital with one electron, not two valence electrons.