Molecular Geometry, Hybridization, and Polarity of SiS2 Lewis Structure

Silicon disulfide has the chemical formula SiS2, and it is an inorganic molecule that is polymeric in nature. It has sulphide bridges in the form of endless SiS4 tetrahedron chains that share their edges. Furthermore, despite how similar silicon disulfide and silicon dioxide (SiO2) are in appearance, their three-dimensional structures are vastly different.

The use of this chemical compound for energy storage has sparked controversy. It’s used to make cathodes for various solid-state batteries, including lithium-sulfur batteries, which are the way of the future.

Furthermore, because of its optical and photovoltaic qualities, silicon disulfide is employed in electronic and chemical applications, as well as solar power.

Silicon disulfide is compatible with sulphates and is water and acid soluble in large amounts. It can be made by heating silicon and sulphur together, or by exchanging silicon dioxide (SiO2) for aluminium sulphide (Al2S3).

Silicon sulphide hydrolyzes quickly to form hydrogen sulphide (H2S), a key gas in anaerobic digestion. It’s important to remember that, regardless of how dangerous silicon disulfide is, it’s readily available in submicron and nanopowder in large quantities. This emphasises the importance of learning about silicon disulfide’s Lewis structure and associated characteristics.

Electrons of Valence

The electrons in an atom’s outermost shell are known as valence electrons because they participate in bond formation. Because these electrons are the furthest from the nucleus, even the tiniest excitation causes them to exit their shell and establish bonds.

The octet rule states that an atom can contain a maximum of 8 valence electrons, although some elements defy this by expanding their outermost shell to accommodate more.

Sulfur is an example of a chemical element whose octet can be expanded to accommodate extra valence electrons.

Silicon disulfide has a Lewis structure (SiS2)

It is critical to examine the Lewis structures of the component atoms, Silicon and Sulfur, before examining the Lewis structure of Silicon disulfide. Silicon has an atomic number of 14 and an electrical structure of 1s2 2s2 2p6 3s2 3p2.

Because the p shell can only hold a maximum of 6 valence electrons, there is a shortage of 4 electrons, resulting in a total of 4 valence electrons in silicon.

Sulfur, on the other hand, has an atomic number of 16 and an electronic structure of 1s2 2p6 3s2 3p4. Because the p shell can only hold six electrons, there is a shortage of two, thus the electrons in the 3s and 3p shells combine to generate the total number of valence electrons, which is six.

The lewis dot structure of Silicon and Sulfur is shown separately below.

Let’s look at the steps that go into drawing the Lewis structure of Silicon disulfide (SiS2):

Step 1: Count how many valence electrons are available to draw one molecule of silicon disulfide: It is 16 because each silicon atom contributes 4 and each sulphur atom contributes 6.

Step 2: Count how many more electrons are needed to make a stable silicon disulfide molecule: It is eight because each silicon atom requires four valence electrons and each sulphur atom requires two.

Step 3: On one silicon disulfide molecule, look for the centre atom: The core atom is a chemical element that exists as a single entity. Because silicon is only one atom, it is the core atom and will be depicted in the middle.

Step 4: Examine the bond that is formed between the atoms involved: Only by forging shared double covalent connections between the involved atoms would the silicon disulfide be able to maintain its molecular structure.

Step 5: Combine all of the above steps and draw the Lewis diagram of Silicon disulfide as follows:

Silicon Disulfide Molecular Geometry (SiS2)

A three-dimensional representation of the atoms that make up a molecule is known as molecular geometry. Bond length, bond type, bond angle, and other geometrical factors can all be easily examined using molecular geometry.

The trigonal bipyramidal, linear, tetrahedral, trigonal planar, and octahedral are the five main forms of geometrical shapes, with the linear being the simplest.

Because the bond angle between the sulphur, silicon, and sulphur atoms is 180 degrees, the silicon disulfide is a triatomic molecule with a linear molecular geometry. This phenomenon can be analysed using the Valence Shell Electron Pair Repulsion (VSEPR) hypothesis, which states that both sulphur atoms have an identical amount of lone pairs of electrons, which create repulsion forces in the opposite direction.

Due to these equal strong repulsion forces exerting equal pressure in opposite directions with similar strength, the shape shifts from bent to linear.

It’s critical to realise that the crystal structure of silicon disulfide (SiS2) is made up of a series of edge-sharing SiS4 tetrahedrons held together by Van der Waals forces of attraction.

Silicon disulfide hybridization (SiS2)

Hybridization is a chemical concept that describes how atomic orbitals mix and overlap to form new hybrid orbitals with the same energy. The molecular shape and bonding characteristics of the new molecule are formed by these newly produced orbitals.

It’s mostly a diagrammatic representation of the orientation of different valence electrons during bonding creation and how they come together to form a new molecule.

In silicon disulfide (SiS2), the silicon atom is sp hybridised, which means that only one s and one p orbital in the same shell of an atom mix and overlap to form two new equivalent orbitals in terms of energy.

The best technique to determine our sp hybridization is to see if the molecule is linear with a 180° bond angle. The Valence Bond Theory predicts that newly created sp hybridised orbitals will have 50% s and p character each.

In addition, sp hybridization is often referred to as diagonal hybridization. It’s vital to remember that any centre atom in a molecule surrounded by two valence electron densities will always exhibit sp hybridization, as in silicon disulfide (SiS2).

Silicon disulfide polarity (SiS2)

The separation of electric charges within an atom is caused by polarity, a chemical feature. Within an atom, this results in the production of two ends, one positively charged and the other negatively charged.

Furthermore, the separation of charges makes an atom more reactive to its surroundings, where even the tiniest excitation causes bond formation, resulting in the synthesis of a new molecule with entirely different features.

To begin evaluating the polarity of Silicon disulfide (SiS2), it is necessary to first look for the presence of a lone pair of electrons. The silicon disulfide is primarily a double-bonded network of silicon and sulphur atoms. The silicon-sulfur (Si-S) bond is polar because each sulphur atom has two lone pairs of electrons.

However, because the silicon disulfide molecule is non-polar, it exhibits an abnormality. Because the polar connections formed are of identical intensity, their effects cancel out, resulting in a net dipole moment of zero. The silicon disulfide (SiS2) molecule is non-polar as a result of this.

Conclusion

The silicon disulfide (SiS2) molecule is a polymer that is both inorganic and organic. The Lewis structure is what governs the molecule’s physical and chemical properties, including why it is combustible in nature. In a higher energy state, the existence of lone pairs of electrons makes the molecule very active. These lone pairs of electrons also modify the molecule’s molecular geometry from bent to linear, resulting in a 180° bond angle.

Because the linear molecular shape encourages sp hybridization, silicon disulfide follows suit, despite the fact that the molecule’s polarity is non-polar.

Read more: Molecular Geometry, Hybridization, and Polarity of HNO2 Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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