Which of the following statements correctly describes the Lewis dot structure of the ammonium ion (NH_4^+)?

• A. Nitrogen is double-bonded to one hydrogen and single-bonded to three hydrogens.
• B. Nitrogen is surrounded by four single bonds to hydrogen atoms and carries a positive formal charge.
• C. Nitrogen is bonded to three hydrogen atoms and has one lone pair.
• D. Each hydrogen atom in NH_4^+ has a lone pair of electrons.

Answer: (B)

Verified step by step guidance

1. Recall that the ammonium ion (NH_4^+) consists of one nitrogen atom bonded to four hydrogen atoms with an overall positive charge.
2. Draw the nitrogen atom in the center and connect it to four hydrogen atoms using single bonds, since nitrogen typically forms three bonds but can expand its bonding in ions like NH_4^+.
3. Count the total valence electrons: nitrogen has 5 valence electrons, each hydrogen has 1, so for NH_4, total is 5 + 4(1) = 9 electrons. Since the ion has a +1 charge, subtract one electron, resulting in 8 electrons to place in the structure.
4. Distribute these electrons as bonding pairs between nitrogen and each hydrogen, resulting in four single bonds. There are no lone pairs left on nitrogen because all electrons are used in bonding.
5. Assign formal charges: nitrogen shares all its valence electrons in bonds, but because of the positive charge on the ion, nitrogen carries a +1 formal charge, and each hydrogen is neutral.