Which of the following is the correct electron configuration for fluorine (atomic number 9)?

• A. 1s^2 2s^2 2p^4
• B. 1s^2 2s^2 2p^5
• C. 1s^2 2s^2 2p^6
• D. 1s^2 2s^2 2p^3

Answer: (B)

Verified step by step guidance

1. Step 1: Identify the atomic number of fluorine, which is 9. This means fluorine has 9 electrons to be placed in atomic orbitals according to the Aufbau principle.
2. Step 2: Recall the order of filling orbitals: 1s, 2s, then 2p. The 1s orbital can hold up to 2 electrons, so fill 1s with 2 electrons: \$1s^{2}$.
3. Step 3: Next, fill the 2s orbital, which can also hold 2 electrons: \$2s^{2}$. Now, 4 electrons have been placed (2 in 1s and 2 in 2s).
4. Step 4: The remaining electrons (9 total - 4 placed = 5 electrons) go into the 2p orbitals. Since 2p can hold up to 6 electrons, place 5 electrons as \$2p^{5}$.
5. Step 5: Combine all parts to write the full electron configuration for fluorine: \$1s^{2} 2s^{2} 2p^{5}$. This matches the correct electron configuration.