Draw the Lewis structure for silicon disulfide, SiS2. How many bonding electron pairs are in a silicon disulfide molecule?
The Correct Answer and Explanation is :
To determine the Lewis structure of silicon disulfide (SiS₂), follow these steps:
- Count the total valence electrons:
- Silicon (Si) has 4 valence electrons.
- Sulfur (S) has 6 valence electrons.
- Total for SiS₂ = 4 + (6 × 2) = 16 valence electrons.
- Arrange the atoms:
- Silicon (Si) is the central atom, as it is less electronegative than sulfur.
- Place the two sulfur atoms on either side of silicon.
- Form bonds between Si and S atoms:
- Start by placing a single bond (2 electrons) between silicon and each sulfur atom. This uses 4 electrons, leaving 12.
- Complete the octets for the sulfur atoms:
- Each sulfur atom requires 6 more electrons to complete its octet. Adding these uses 12 electrons, which exhausts the total 16 available valence electrons.
- Check the octet rule:
- Silicon has only 4 electrons from the single bonds. To satisfy its octet, move lone pairs from sulfur to form double bonds. Both sulfur atoms will form a double bond with silicon.
- Verify formal charges:
- All atoms have a formal charge of zero, confirming the most stable structure.
Final Lewis Structure:
- Silicon forms two double bonds with the sulfur atoms (S=Si=S).
- There are no lone pairs on silicon, while each sulfur atom has two lone pairs.
Number of Bonding Electron Pairs:
- Each double bond contains 4 bonding electrons, or 2 bonding pairs.
- Total bonding pairs in SiS₂ = 2 (from each double bond) × 2 = 4 bonding electron pairs.
Explanation (300 words):
Silicon disulfide (SiS₂) is a covalent molecule in which silicon forms two double bonds with sulfur atoms. Silicon, in group 14, tends to form four bonds to complete its octet. Sulfur, in group 16, forms two bonds to achieve an octet. By distributing electrons, we prioritize completing the octets of the more electronegative sulfur atoms, adjusting to form multiple bonds as needed to balance silicon’s octet.
Each double bond in SiS₂ consists of two bonding pairs of electrons, and the molecule has a linear shape because of its sp hybridization around the silicon atom. Understanding the Lewis structure helps explain chemical bonding, molecular geometry, and reactivity for silicon disulfide.