Molecular Geometry, Hybridization, and Polarity of SiF4 Lewis Structure

The covalent molecule SIF4 is made up of silicon and fluorine atoms. Tetrafluorosilane, or silicon tetrafluoride, is the chemical name for it.

Silicon tetrafluoride has a melting and boiling point of -95.0 °C and -90.3 °C, respectively, and so exists as a gas at normal temperature.

Silicon tetrafluoride has a distinct odour and is colourless, poisonous, corrosive, and non-flammable. In the laboratory, silicon tetrafluoride is made by decomposing BaSiF6 at temperatures above 300 °C.

BaSiF6    —–>     SiF4 (volatile)   +   BaF2 (residue)

Because of the volatile nature of silicon tetrafluoride, its applications are limited to organic synthesis and microelectronics.

SiF4 has a density of 1.66 g/cm3, making it heavier than air. It has a molar mass of 104 grammes per mol.

In this article, we’ll look at the chemical bonding of silicon tetrafluoride by looking at its Lewis structure, molecular geometry, and central atom hybridization. Then we’ll look at SiF4’s polarity, or whether it’s a polar or nonpolar molecule.

Lewis Structure of SiF4

To begin, it is necessary to comprehend the Lewis structure of silicon tetrafluoride in order to examine its chemical bonding.

The Lewis structure is a two-dimensional depiction of a molecule in which the atoms are surrounded by valence electrons. The valence electrons, or atoms’ outermost shell electrons, are depicted as dots, giving rise to the phrase “electron dot structure.”

Let’s make a diagram of silicon tetrafluoride’s Lewis structure.

Step 1: Determine how many valence electrons are present in silicon tetrafluoride.

One silicon atom and four fluorine atoms make up silicon tetrafluoride. The atoms of silicon and fluorine are in groups 14 and 17, respectively. As a result, the silicon atom has four valence electrons while the fluorine atom has seven.

As a result, silicon tetrafluoride has a total of 4 + (7*4) = 32 valence electrons.

Step 2: Identify the silicon tetrafluoride centre atom.

Silicon is the less electronegative of the silicon and fluorine atoms, making it the centre atom in silicon tetrafluoride. The silicon atom will be surrounded by four fluorine atoms.

Step 3: Using the octet rule, organise all valence electrons in silicon tetrafluoride.

Every element in the periodic table (excluding Hydrogen and Helium) tends to have a noble gas configuration when forming a chemical bond with another atom, according to the octet rule.

The 32 valence electrons in silicon tetrafluoride have been grouped in the following diagram:

Both silicon and fluorine have eight electrons in their outermost shell, indicating that they have completed their octet.

Let us now compute the formal charge on the silicon and fluorine atoms in SiF4, which is:

Number of valence electrons – 1/2(bonding electrons) – nonbonding electrons = formal charge

Si = 4 12(8) 0 = 0 is the formal charge on the Silicon atom.

F = 7 12(2) 6 = 0 is the formal charge on the fluorine atom.

As a result, in the Lewis structure of silicon tetrafluoride, the silicon and fluorine atoms have no charge. In silicon tetrafluoride, two electrons shared by the silicon and fluorine atoms create a single link. As a result, the best Lewis structure for silicon fluoride in bond notation is:

Silicon tetrafluoride’s Lewis structure reveals that the silicon atom forms four single bonds with four fluorine atoms.

The Lewis structure is the cornerstone of any molecule’s chemical bonding. We can predict the molecular geometry of silicon tetrafluoride using Lewis structure and Valence shell electron pair repulsion (VSEPR) theory.

Molecular Geometry of SiF4

The molecular geometry and hybridization of the silicon atom in silicon tetrafluoride must be understood in order to cast further light on the chemical bonding of nitryl fluoride.

A three-dimensional depiction of the molecule is called molecular geometry or form. With the help of the Lewis structure, VSEPR theory determines it.

The form of the molecule is determined by repulsion between the valence shell electrons, which might be bonding or non-bonding electrons, according to VSEPR theory.

The silicon atom is the core element in silicon tetrafluoride, and it forms four sigma bonds with four fluorine atoms, as seen in its Lewis structure. Because the silicon atom has no lone pair of electrons, the following table can be used to determine its molecular geometry or shape:

General formulaNumber of bond pairsMolecular shape/geometry
AX1Linear
AX22Linear
AX33Trigonal planar
AX44Tetrahedral
AX55Trigonal bipyramidal
AX66Octahedral

A is the centre atom in the table above, and X is the surrounding atom that is connected to the central atom. Because all of the X atoms, namely the fluorine atom, are the same, the silicon tetrafluoride molecule will have optimal tetrahedral geometry.

Two Si-F bonds are in a plane in silicon tetrafluoride’s tetrahedral geometry, one Si-F bond is above the plane, and another Si-F bond is below the plane.

The F-Si-F bond angle of silicon tetrafluoride is 109.5 degrees due to its tetrahedral shape. The Si-F bond has a length of 154 pm.

Let’s go on to studying about the silicon atom’s hybridization in silicon tetrafluoride.

Hybridization of SiF4

The Valence Band Theory is important to understand the hybridization of the silicon atom in silicon tetrafluoride (VBT).

This theory provides information about the molecule’s core atom’s hybridization. The core atom’s hybrid orbitals, generated by merging atomic orbitals of similar energy, overlap with the atomic orbitals of another atom, according to VBT. The development of a covalent bond is caused by the orbitals overlapping.

Let’s use VBT to figure out how the silicon atom, Si, in the SiF4 molecule hybridises.

The electrical configuration of the silicon atom in its ground state will be [Ne] 3s23p2. In the ground state, there are two unpaired electrons. However, according to the Lewis structure of silicon tetrafluoride and the VSEPR theory, the silicon atom forms four sigma bonds.

As a result, one of the electrons from the 3s orbital excites the silicon atom’s 3p orbital, resulting in four unpaired electrons enabling the creation of four sigma bonds with four fluorine atoms. It results in the [Ne] 3s13p3 excited state configuration of the silicon atom.

With a bond angle of 109.5 degrees, these four sp3 hybrid orbitals form a tetrahedral shape. Four sp3 hybrid orbitals will collide with four fluorine atoms’ 2p orbitals, forming four Si F covalent bonds.

As a result, in silicon tetrafluoride, the silicon atom undergoes sp3 hybridization with tetrahedral geometry.

The steric number can also be used to determine the silicon atom’s hybridization and the geometry of the silicon tetrafluoride. The steric number is calculated as follows:

Number of atoms linked to the centre atom + number of lone pairs coupled to the central atom equals steric number.

Four fluorine atoms are linked to the silicon atom in SiF4, and the silicon atom has no lone pair.

As a result, the steric number of silicon tetrafluoride is four, indicating SiF4’s tetrahedral geometry and the silicon atom’s sp3 hybridization.

Let us now look at how polarity works in silicon tetrafluoride.

Polarity of SiF4

Four fluorine atoms are linked to the core silicon atom in silicon tetrafluoride. The electronegativity values of silicon and fluorine atoms, according to the Pauling scale, are 1.90 and 3.98, respectively. The Si-F bond has an electronegativity differential of 3.98 – 1.90 = 2.08.

The electron pair is highly attracted to the fluorine atom, as evidenced by the large electronegativity difference. As a result, the Si-F bond is extremely polar, acting as a dipole with a partial negative charge on the fluorine atom and a partial positive charge on the silicon atom, respectively.

Silicon tetrafluoride has a tetrahedral molecular geometry, according to VBT and VSEPR theory. Because the tetrahedral geometry is symmetrical, the Si-F bond’s polarities balance out. It causes the silicon tetrafluoride to have a net dipole moment of zero.

Despite the extremely polar character of the Si F link, silicon tetrafluoride is a nonpolar molecule.

Conclusion

The chemical bonding of silicon tetrafluoride or tetrafluorosilane has been learnt here.

In silicon tetrafluoride, the silicon atom is the core element, and it forms four sigma bonds with four fluorine atoms. The molecular geometry of silicon tetrafluoride is tetrahedral, with sp3 hybridization at the central silicon atom. Silicon tetrafluoride is a nonpolar compound due to its symmetrical molecular structure.

Thank you very much.

Take pleasure in learning.

Read more: Is KNO3 a Base or an Acid?

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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