Draw the Lewis Structure for SOCl2: Is It Necessary to Employ an Expanded Valence Shell?

To draw the Lewis structure for sulfur dichloride oxide (SOCl₂), we need to follow a few steps to ensure we correctly represent the molecules’ bonds and valence electrons.

1. **Count the Valence Electrons:** Sulfur (S) has 6 valence electrons, oxygen (O) has 6 valence electrons, and each chlorine (Cl) has 7 valence electrons. Therefore, the total number of valence electrons for SOCl₂ is:

6 (S) + 6 (O) + 2 × 7 (Cl) = 26 valence electrons.

2. **Arrange the Atoms:** Sulfur will be the central atom because it can form multiple bonds. Chlorine and oxygen will surround it. A possible arrangement is S in the center, with O and two Cl atoms attached to it.

3. **Connect the Atoms with Bonds:** Let’s start by forming single bonds between sulfur and each chlorine atom, and a double bond with oxygen. This gives us:

  Cl-S=O
    |  
    Cl

4. **Distribute the Remaining Electrons:** After forming the bonds, we must allocate the remaining electron pairs to complete the outer shells of the atoms. Each Cl has 6 electrons around it in the form of 3 lone pairs (3 pair = 6 electrons), while O has 2 electrons in the bond with S and 2 lone pairs. The final count of electron distribution will look like this:

   ..  ..
   :Cl:  :Cl:
    |     |
  .. S=O ..
   ..  ..

5. **Check for Octets:** Each atom in the molecule should have a full outer shell or octet where applicable. The structure above gives us an octet for the Cl and O atoms, while sulfur has 12 electrons around it. This leads to the next part of the question.

Regarding the necessity of an expanded valence shell, sulfur is in Period 3 of the periodic table and can expand its valence shell beyond the octet rule due to the availability of d-orbitals. Therefore, it is not only acceptable but also necessary to use an expanded valence shell for S in SOCl₂ to accommodate the additional electrons when forming the structure. This is a common characteristic seen in molecules where the central atom is from the third period or below.

In conclusion, the Lewis structure for SOCl₂ can be successfully drawn without needing to expand the octet for the surrounding atoms (Cl and O) but must do so for sulfur to satisfy all bond configurations.