SiCl4 is the chemical formula of silicon tetrachloride. It is a colorless volatile liquid that fumes in the air. It is used to produce high-purity silicon and silica for commercial applications. SiCl4 has a molar mass of 169.9 g/mol.
If you have a query regarding the polarity of the silicon tetrachloride (SiCl4) molecule and want to know whether it is polar or non-polar, you are at the right place.
So, let’s get started.
Is SiCl4 polar or non-polar?
Silicon tetrachloride (SiCl4) is a non-polar molecule. It consists of one silicon (Si) atom and four chlorine (Cl) atoms. The silicon is kept at the central position while all four chlorine atoms occupy surrounding positions, making a perfectly symmetrical tetrahedral molecular shape and geometry.
An electronegativity difference of 1.26 units exists between the bonded atoms of silicon and chlorine in each Si-Cl bond in SiCl4. Thus, each Si-Cl bond is individually polar in SiCl4 and possesses a specific dipole moment value (symbol µ).
In the SiCl4 molecule, the highly electronegative chlorine atom more strongly attracts the shared electron cloud from each Si-Cl bond.
However, as no lone pair of electrons is present on the central silicon atom, thus, the charged electron cloud stays uniformly distributed overall.
Due to the symmetrical tetrahedral shape of the SiCl4 molecule, the dipole moments of individually polar Si-Cl bonds get canceled equally. As a result, the SiCl4 molecule is overall non-polar (net µ = 0).
A molecule is polar if there is a non-uniform charge distribution present in it.
If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
The electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now, let us discuss the effect of the above three factors one by one to prove that the silicon tetrachloride (SiCl4) is overall a non-polar molecule.
Factors affecting the polarity of SiCl4
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Silicon (Si) is present in Group 14 of the Periodic Table. The electronic configuration of silicon is 1s2 2s2 2p6 3s2 3p2. As per the electronic configuration, a Si-atom has a total of 4 valence electrons; it is thus short of 4 more electrons that are required so that the silicon atom can achieve a complete octet electronic configuration.
Conversely, chlorine (Cl) is present in Group 17 of the Periodic Table. The electronic configuration of a chlorine atom is 1s2 2s2 2p6 3s2 3p5. As per this electronic configuration, a Cl-atom has a total of 7 valence electrons; it is thus short of one valence electron that is required so that the chlorine atom can achieve a complete octet electronic configuration.
The Lewis dot structure of SiCl4 shows that there are four Si-Cl bonds. All four valence electrons of silicon used in covalent bonding denote there is no lone pair of electrons present on the central Si-atom in SiCl4.
Contrarily each terminal Cl-atom contains 3 lone pairs of electrons. In this way, all bonded atoms attain a completely stable octet electronic configuration via lone pairs and chemical bonding in SiCl4.
Due to the absence of any lone pair of electrons on the central Si-atom in SiCl4, there is no distortion in the symmetrical tetrahedral shape or geometry of the molecule.
Atom
Electronic configuration
Valence electrons
Silicon (14Si)
1s2 2s2 2p6 3s2 3p2
4
Chlorine (17Cl)
1s2 2s2 2p6 3s2 3p5
7
The electronegativity difference in SiCl4 between Si-atom (E.N= 1.90) and Cl-atom (E.N= 3.16) in each of the four Si-Cl bonds is 1.26 units.
Hence, the chlorine atom with relatively higher electronegativity gains a partial negative (Clδ-) charge while the silicon atom obtains a partial positive (Siδ+) charge (as shown below).
As a result, in SiCl4, all Si-Cl bonds are individually polar with an electronegativity difference of 1.26 units.
Dipole Moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.
So in polar bonds of SiCl4, the dipole moment of each Si-Cl bond points from Siδ+ to Clδ-(as shown below).
Molecular geometry
According to the valence shell electron pair (VSEPR) theory of chemical bonding, SiCl4 is an AX4E0 or simple AX4-type molecule. To one Si-atom at the center (A), four bonded atoms (X) are attached (four Cl-atoms), and the central Si-atom contains no lone pair of electrons (E).
The molecular geometry or shape of SiCl4 is tetrahedral, which is identical to its electron pair geometry. To minimize bond pair-bond pair repulsions and to attain stability in the tetrahedral structure, the bonded atoms of the SiCl4 molecule possess a mutual bond angle of (∠Cl-Si-Cl) 109.5°.
Due to the absence of any lone pair of electrons on the central Si-atom, SiCl4 has an identical molecular and electron geometry that is tetrahedral.
Highly electronegative Cl-atoms attract the shared cloud of each Si-Cl to a large extent. Hence, the Si-Cl bonds are individually polar.
Still, due to the symmetrical tetrahedral shape of SiCl4, the overall charged electron cloud stays uniformly distributed as the Si-Cl dipole moments get canceled equally in the molecule.
The net dipole moment of three downwards-pointing Si-Cl bonds gets canceled with the dipole moment of an upwards-pointing Si-Cl bond. Consequently, silicon tetrachloride (SiCl4) is overall a non-polar molecule (net µ = 0).
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), nitric oxide (NO), carbonyl sulfide (OCS or COS), etc.
SiCl4 has four Si-Cl bonds. The electronegativity difference between the bonded Si-atom (E. N= 1.90) and Cl-atom (E. N= 3.16) is 1.26 units. Therefore, the Cl-atom gains a partial negative (Clδ-) charge while the central Si-atom obtains a partial positive (Siδ+) charge.
Each Si-Cl bond thus possesses a particular dipole moment Hence, each Si-Cl bond in SiCl4 is individually polar.
However, it is due to the symmetrical tetrahedral shape of SiCl4 that the individual Si-Cl dipole moments get canceled. The electron cloud stays uniformly distributed in the molecule overall.
Thus, SiCl4 is overall a non-polar molecule with µ = 0.
SiCl4 contains polar bonds but is more soluble in a non-polar solvent. Why?
In SiCl4, each Si-Cl bond is polar due to an electronegativity difference of 1.26 units between the bonded Si-atom (E. N= 1.90) and Cl-atom (E. N= 3.16).
Still, as it has a symmetrical tetrahedral molecular geometry, the dipole moments of individually polar Si-Cl bonds get canceled, making SiCl4 molecule overall non-polar.
Hence, non-polar SiCl4 is soluble in non-polar solvents as per the concept of like dissolves like.
Which one out of these is a polar molecule?
i) CCl4 , ii) SiCl4 and iii) SiH4
All the above molecules arenon-polar.
i) Tetra chloromethane (CCl4) has four polar C-Cl bonds due to an electronegativity difference of 0.61 units between the bonded atoms.
ii) Silicon tetrachloride (SiCl4) has an electronegativity difference of 1.26 units between a silicon and chlorine atom.
iii) Silicon tetrahydride (SiH4) has a small electronegativity difference of 0.3 units between a silicon and a hydrogen atom.
However, all the above three molecules possess a symmetrical tetrahedral shape and geometry.
Thus the dipole moments of individually polar bonds get uniformly canceled on each side of the molecule.
The overall charged electron cloud stays uniformly spread, leading to a net dipole moment µ = 0.
Why is NH3 polar while SiCl4 is a non-polar molecule?
Thus the dipole moments of individually polar N-H bonds do not get canceled uniformly, and NH3 is overall polar (net µ = 1.46 D).
Contrarily, SiCl4 has a symmetrical tetrahedral shape and geometry. The dipole moments of individually polar Si-Cl bonds get canceled uniformly on each side of the molecule. It is thus overall non-polar (net µ = 0).
Is there a formal charge on the bonded atoms in the SiCl4 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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