Silicon disulfide (SiS2) is a covalent compound consisting of silicon (Si) and sulfur (S) atoms. To determine the number of pairs of non-bonding electrons in a silicon disulfide molecule, we can first calculate the total number of valence electrons in the molecule.
Silicon (Si) has 4 valence electrons, and sulfur (S) has 6 valence electrons each. Since there are two sulfur atoms in SiS2, that's a total of 2 x 6 = 12 valence electrons from sulfur.
Now, add the valence electrons from silicon and sulfur:
4 (Si) + 12 (S) = 16 valence electrons in total.
In a covalent compound like silicon disulfide, all the valence electrons are involved in bonding, either in forming bonds (shared electrons) or as non-bonding pairs.
Since SiS2 forms two covalent bonds (Si-S-Si), each involving two electrons, there are 4 electrons used for bonding (2 pairs of bonding electrons). Therefore, the remaining 16 - 4 = 12 electrons are non-bonding pairs.
So, there are 12 pairs of non-bonding electrons in a silicon disulfide (SiS2) molecule.