Draw Lewis Structure for ASO3 3

To draw the Lewis structure for ASO₃^3-, we begin by determining the total number of valence electrons available.

1. **Count the Valence Electrons**:

• Arsenic (As) has 5 valence electrons.
• Oxygen (O) has 6 valence electrons and there are three oxygen atoms, contributing a total of 18 valence electrons (3 × 6).
• Since the molecule has a 3- charge, we add 3 more electrons.

This gives us a total of: 5 (As) + 18 (3 O) + 3 (charge) = 26 valence electrons.

2. **Sketch the Skeleton Structure**:

Place arsenic (As) at the center and connect it to the three oxygen atoms with single bonds.

3. **Distribute Remaining Electrons**:

Initially, we used 6 electrons for the three As-O bonds, leaving us with 20 electrons to place. We start by fulfilling the octet rule for the oxygen atoms, adding 6 electrons (3 lone pairs) to each of the three O atoms. This utilizes 18 electrons, leaving us with 2 electrons.

4. **Form Double Bonds**:

Since arsenic can expand its octet, we can use the remaining 2 electrons to form a double bond between arsenic and one of the oxygen atoms. This ensures that one oxygen atom shares a total of 4 electrons with arsenic, achieving a stable octet for both atoms.

5. **Add Formal Charges**:

After arranging the electrons, check the formal charges. Oxygen with a double bond will have a formal charge of 0, while the other two oxygens with 3 lone pairs will have formal charges of -1 (for each). The arsenic will also have a formal charge of +1, which is acceptable for the molecule’s overall charge of -3.

6. **Final Structure**:

The final Lewis structure of ASO₃^3- looks like this:

       O        O        O
        ||      ..       ..
        As  -  O  -  O

In conclusion, the Lewis structure for ASO₃^3- exhibits double and single bonds that cater to the valence requirements and charge of the molecule.