How many lone pairs of electrons are on the As atom in the Lewis dot structure of AsF₃?

• A. 3 lone pairs
• B. 1 lone pair
• C. 0 lone pairs
• D. 2 lone pairs

Answer: (B)

Verified step by step guidance

1. Step 1: Begin by identifying the total number of valence electrons available for the molecule AsF₃. Arsenic (As) is in group 15 of the periodic table, which means it has 5 valence electrons. Fluorine (F) is in group 17, so each fluorine atom has 7 valence electrons. Since there are three fluorine atoms, the total number of valence electrons from fluorine is 3 × 7 = 21.
2. Step 2: Add the valence electrons from arsenic and fluorine to find the total number of valence electrons in AsF₃. This is 5 (from As) + 21 (from 3 F atoms) = 26 valence electrons.
3. Step 3: Construct the Lewis structure by placing the arsenic atom in the center and arranging the three fluorine atoms around it. Connect each fluorine atom to the arsenic atom with a single bond. Each bond uses 2 electrons, so 3 bonds use 6 electrons.
4. Step 4: Distribute the remaining electrons to satisfy the octet rule for each atom. Start by completing the octets for the fluorine atoms. Each fluorine atom needs 8 electrons, including the bonding pair. Since each fluorine already has 2 electrons from the bond, place 6 more electrons (3 lone pairs) around each fluorine atom.
5. Step 5: After placing electrons around the fluorine atoms, check the number of electrons used. You have used 6 electrons for bonds and 18 electrons for the lone pairs on fluorine, totaling 24 electrons. The remaining 2 electrons are placed as a lone pair on the arsenic atom, completing its octet.