Draw the electron dot formula for silicon disulfide, sis2. How many nonbonding electron pairs are in a silicon disulfide molecule?
The Correct Answer and Explanation is:
To draw the electron dot formula (also known as the Lewis structure) for silicon disulfide (SiS₂), we start by determining the total number of valence electrons. Silicon (Si) is in group 14 of the periodic table and has four valence electrons. Each sulfur (S) atom, found in group 16, has six valence electrons. Thus, for SiS₂:
- Silicon contributes: 4 valence electrons
- Sulfur contributes: 2 × 6 = 12 valence electrons
Adding these together gives us a total of ( 4 + 12 = 16 ) valence electrons.
Drawing the Lewis Structure
- Arrange the Atoms: In SiS₂, silicon is the central atom since it can form more bonds, while the sulfur atoms will be on either side. The initial structure is:
[
S – Si – S
] - Form Bonds: Each S atom forms a single bond with the Si atom. Each bond consists of two electrons, so two bonds account for ( 2 \times 2 = 4 ) valence electrons. After forming the bonds, we have ( 16 – 4 = 12 ) valence electrons left.
- Distribute Remaining Electrons: Place the remaining electrons around the sulfur atoms. Each sulfur needs a total of 8 electrons to complete its octet. Each sulfur already has 2 electrons from the bond with silicon. Thus, we need to add 6 more electrons to each sulfur. This can be done by placing 3 lone pairs around each sulfur atom:
[
\begin{array}{cccc}
:S: & – & :Si: & – & :S: \
: & & : & & : \
: & & : & & :
\end{array}
] - Final Structure: The final Lewis structure for SiS₂ shows the central Si atom bonded to two S atoms, each with three lone pairs, ensuring all atoms have a complete octet.
Nonbonding Electron Pairs
In silicon disulfide (SiS₂), each sulfur atom has three lone pairs of electrons. Since there are two sulfur atoms, the total number of nonbonding electron pairs in a SiS₂ molecule is:
[
2 \text{ (S)} \times 3 \text{ (lone pairs)} = 6 \text{ nonbonding electron pairs}
]
Thus, silicon disulfide contains 6 nonbonding electron pairs. This structure illustrates the importance of octet completion for stability and how the arrangement of electrons affects the molecule’s geometry and reactivity. The presence of nonbonding pairs can influence molecular shape and polarity, making these considerations crucial in understanding chemical behavior.