This chemical compound has been under scrutiny because of its usage for energy storage. It is used in the production of cathodes for different solid-state batteries because of which lithium-sulfur batteries are becoming the future. Moreover, silicon disulfide is used in electronic and chemical products along with, solar power because of having great potential due to its optical and photovoltaic properties. Silicon disulfide has good compatibility with sulfates where it is substantially soluble in water and acid. It can be produced by heating silicon and sulfur or through the exchange reaction between silicon dioxide (SiO2) and aluminum sulfide (Al2S3). Silicon sulfide readily hydrolyzes to produce hydrogen sulfide (H2S) which is an important gas in anaerobic digestion. It is crucial to realize that irrespective of how toxic this compound is, silicon disulfide is available in submicron and nanopowder in high volumes. This makes it even more important to read about the Lewis structure of silicon disulfide and its associated properties.
Valence Electrons
As the outermost shell of an atom participates in the bond formation, the electrons present in it are called valence electrons. As these electrons are farthest from the nucleus, they readily leave their shell even with the slightest excitation to undergo bond formation. As per the octet rule, the maximum number of valence electrons an atom can have is 8, whereas some elements do not follow it by accommodating more by expanding their outermost shell. One example of a chemical element that can expand its octet to accommodate more valence electrons is Sulfur.
Lewis structure of Silicon disulfide (SiS2)
Before studying the Lewis structure of Silicon disulfide, it is crucial to analyze the Lewis structures of participating atoms which are Silicon and Sulfur. The atomic number of Silicon is 14, and the electronic configuration is 1s2 2s2 2p6 3s2 3p2. As p shell can accommodate a maximum of 6 valence electrons, there is a dearth of 4 electrons because of which the total number of valence electrons in silicon is 4. On the other hand, the atomic number of sulfur is 16 and the electronic configuration is 1s2 2s2 2p6 3s2 3p4. As p shell can accommodate 6 electrons, there is a dearth of two electrons, the ones in the 3s and 3p shells together forms the total number of valence electrons which is 6. Below is the image of the lewis dot structure of Silicon and Sulfur separately.
Now let us study the steps involved to draw the Lewis structure of Silicon disulfide (SiS2): Step 1: Note down the total number of valence electrons available to draw one molecule of silicon disulfide: It is 16 as 4 are coming from silicon atom and 6 are coming from each sulfur atom. Step 2: Note down how many more electrons are required to form a stable one silicon disulfide molecule: It is 8 as 4 are needed by the silicon atom and two valence electrons are needed by each sulfur atom. Step 3: Look for the central atom on one silicon disulfide molecule: The chemical element present as a single entity is considered as the central atom. Silicon is present as a single atom so it is the central atom and will be drawn at the center. Step 4: Check the bond forming between the participating atoms: The shared double covalent bonds are forming between the participating atoms as only then the silicon disulfide will be able to stabilize its molecular structure. Step 5: Now assimilate all the aforementioned steps and draw the Lewis diagram of Silicon disulfide:
Molecular Geometry of Silicon disulfide (SiS2)
Molecular geometry is a dimensional drawing of the atoms that are forming a molecule. Through molecular geometry bond length, bond type, bond angle and other geometrical parameters can be studied easily. There are five main types of geometrical shapes called trigonal bipyramidal, linear, tetrahedral, trigonal planar, and octahedral where the linear is the simplest shape of all. The silicon disulfide is a triatomic molecule where its molecular geometry is linear as the bond angle between the sulfur-silicon-sulfur atoms is 180°. This behavior can be studied with the help of the Valence Shell Electron Pair Repulsion (VSEPR) theory which exerts that the presence of an equal number of lone pairs of electrons on both the sulfur atoms that create repulsion forces in the opposite direction to one another. These equal strong repulsion forces exert pressure in the opposite directions with equal intensity due to which the shape changes from the bent shape to the linear one.
It is crucial to understand that the crystal structure of silicon disulfide (SiS2) is made up of linear chains of edge-sharing SiS4 tetrahedrons which are held together with the help of Van der Waals forces of attraction.
Hybridization in Silicon disulfide (SiS2)
Hybridization is a concept in chemistry that determines how atomic orbitals mix and overlap with one another to produce new hybrid orbitals of equal energy. These newly formed orbitals form the molecular geometry and the bonding properties of the new molecule. It is mainly a diagrammatic representation showing the orientation of different valence electrons while bonding formation and how they are forming a new molecule altogether. The silicon atom in silicon disulfide (SiS2) is sp hybridized as only one s and one p orbital in the same shell of an atom mix and overlaps to produce two new equivalent orbitals in terms of energy. The best way to figure our sp hybridization is whether the molecule is linear with the bond angle of 180° or not. This hybridization behavior can be studied with the help of Valence Bond Theory which says the newly produced sp hybridized orbitals will have 50% s and p character each. Moreover, sp hybridization is also called diagonal hybridization. It is important to realize that any central atom surrounded by two valence electron density within a molecule with always exhibit sp hybridization, which is the case of silicon disulfide (SiS2).
Polarity in Silicon disulfide (SiS2)
Polarity is a chemical property by which the separation of electric charges occurs within an atom. This leads to the formation of two ends within an atom where one is positively charged and the other is negatively charged. Moreover, this separation of charges makes an atom more reactive to its surrounding atoms where even with the slightest excitement, they readily undergo bond formation to produce a new molecule having new properties altogether. To begin with, analyzing the polarity in Silicon disulfide (SiS2), it is first essential to see the presence of lone pair of electrons. The silicon disulfide is mainly a network of silicon and sulfur atoms bonded through double bonds. The silicon-sulfur (Si-S) bond is polar are there exist two lone pairs of electrons of each sulfur atom. However, the silicon disulfide molecule shows an anomaly as the molecule is non-polar in nature. It is because the polar bonds forming are of equal intensity which cancels out the effect of one another making the net dipole moment zero. Due to this the silicon disulfide (SiS2) molecule is non-polar in nature.
Conclusion
The silicon disulfide (SiS2) molecule is an inorganic compound that happens to be a polymer as well. The Lewis structure determines various physical and chemical properties of the molecule especially why it is flammable in nature. It is the presence of lone pairs of electrons that makes the molecule quite active in a higher energy state. These lone pairs of electrons further change the molecular geometry of the molecule from bent shape to linear making the bond angle 180°. As the linear molecular geometry promotes sp hybridization, so the silicon disulfide follows it whereas the polarity of the molecule is non-polar.
