Silicon tetrachloride (SiCl4) is an inorganic compound that is used in commercial applications to produce highly pure silicon or silica. Various silicon compounds such as ferrosilicon, silicon carbide, or mixtures of silicon dioxide and carbon can be chlorinated to prepare SiCl4.
SiCl4 is a colorless volatile liquid, which produces fumes when kept in the moist air. A violent reaction between SiCl4 and water produces white-colored solid silicon dioxide and steamy fumes of HCl. Due to this, the water vapor present in moist air generates fumes of liquid SiCl4.
This article describes the polarity of SiCl4 and the factors that affect it.
So, is SiCl4 polar or nonpolar? SiCl4 is a non-polar compound because of its linear and symmetrical shape. The bonds in the molecule are polar because the chlorine atom is more electronegative than the silicon atom but due to linear and opposite directions of both bonds, the dipoles of both bonds in SiCl4 cancel out each other. Hence, the net dipole moment comes out to be zero, and thus SiCl4 is non-polar.
Let us study the fundamentals of Polarity in more detail.
Why is SiCl4 Nonpolar in nature?
In order to check the polarity of any inorganic compound, three major points have to be analyzed:
- Lewis structure of the compound
- Shape or symmetricity of the compound
- The net dipole moment of the compound
Lewis Structure of SiCl4
Lewis structures, also known as electron-dot structures or electron-dot diagrams, illustrate the bonding between atoms of a molecule, and lone electron pairs that may be present in the molecule.
Lewis structures can be developed for molecules with covalent bonding, as well as for coordination compounds.
In SiCl4, silicon is the center atom of the molecule, and the four valence electrons of the silicon share a single bond with four chlorine atoms around it.
Therefore, there are no lone pairs of electrons on the silicon atom.
Lewis structures provide insight into how an atom will bond and how many bonds it will form.
Eventually, this knowledge can help us to understand the shapes of molecules and their chemical properties.
Shape and Symmetricity of SiCl4
The shape and structure of a molecule also determine the polarity of a compound.
There is a plethora of experimental evidence to support this claim, ranging from their physical properties to their chemical reactivity. Small molecules, or molecules with a single central atom, have predictable shapes.
Valence shell electron pair repulsion (VSEPR) is the fundamental concept in molecular shapes. It is claimed that electron pairs, which are made up of negatively charged particles, repel each other in order to get as far away from each other as possible.
This provides a tetrahedral shape to SiCl4 which has a coordination number of 4.
The presence of symmetry operations performed with respect to symmetry elements determines a molecule’s symmetry.
The symmetry element is a line, a plane, or a point in or through an object about which a rotation or reflection results in an orientation that is indistinguishable from the original.
The Symmetricity of a molecule also plays a major role in determining the polarity of a compound.
In SiCl4, chlorine atoms are placed at an equal distance from each other providing to figure out the clear shape of the molecule.
As the Cl atoms are at an equal distance from each other and from the center atom silicon, they are symmetrical in nature.
Basically, when there is symmetry in molecules, they are predicted to be non-polar in nature. But, in order to confirm, the net dipole moment of the molecule has to be analyzed.
The Net Dipole Moment of SiCl4
The dipole moment is a measure of the polarity of the molecule, that occurs in the presence of charge separation.
The distance between the charge separations also influences the size of the dipole moment.
They occur in ionic bonds or covalent bonds due to the differences in electronegativity. The dipole moment grows in proportion to the difference in electronegativity.
In SiCl4, the electronegativity of the silicon (Si) atom is 1.9 whereas the chlorine (Cl) atom is 3.16. The electronegativity difference between Si and Cl atoms is about 1.26 which is greater than 0.4.
Therefore the single bond between Si-Cl is determined to be polar.
When looking at the dipole moment of the molecule, the four single bonds between the Si-Cl atom are acting in the opposite direction to each other.
Hence, the net dipole moment becomes to be zero which means there are no poles on this compound. Thereby, SiCl4 is regarded as the NON-POLAR compound.
What are Polar and Nonpolar Molecules?
Chemical compounds use various types of bonds to connect their atoms to form the molecule. Ionic, hydrogen, covalent, and metallic molecules are formed by the formation of various types of bonds.
Ionic and covalent bonds are the most common and strong types of bonds.
1. Ionic bond: An ionic bond is formed when two atoms with opposite charges combine to form a molecule.
Two oppositely charged atoms stabilize each other in this case. These bonds are typically used when there is a significant difference in the electronegativities of two atoms.
In such bondings, electrons are completely transferred.
2. Covalent bond: These bonds form when two or more atoms share electrons in order to stabilize one another.
These bonds can be single, double, or triple depending on the number of electrons involved. These bonds may be polar or nonpolar.
Polar Molecule: When the charge distribution of two atoms forming a bond is unequal, the bond is said to be polar.
In such a case, one of the atom’s partial ionic charges increases.
This occurs when there is a large difference in electronegativity between the two atoms.
As a result, a partial ionic charge is formed, with one atom charged highly negatively and another charged highly positively resulting in a polar molecule.
NF3 is one of the best examples of a polar compound. Have a look at the article on the polarity of NF3.
NonPolar Molecule: When two atoms form a covalent bond with symmetry and with an equal ionic charge on both atoms, the resulting molecule is known as a nonpolar molecule.
When the electronegativities of both atoms are the same, a non-polar bond is formed. One example of such a compound is BeH2.
Check out the article on the polarity of BeH2.
1. SiCl4 is used to produce semiconducting silicon.
2. It is used to synthesize silica gel, silicic esters, and a binder for ceramic materials.
3. It is used in producing smoke screens in warfare due to its fuming nature.
4. It plays a major role in manufacturing transistors.
5. It is used in the manufacturing of highly pure silica for solar cells and fused silica glass.
6. It is used as an adhesive and sealant chemical in industries.
7. It is used as a reactant or raw material in the polysilicon manufacturing process.
8. SiCl4 is the synthesizing material for the manufacture of optical fibers.
SiCl4 General Facts
1. The molecular weight of SiCl4 is 169.9
2. It is a clear, colorless, mobile, and fuming liquid with a suffocating odor.
3. The boiling point of SiCl4 is 135.7 °F (57 °C) whereas, the melting point is -94°F (-70 °C)
4. The hybridization of the SiCl4 molecule is sp3
5. The bond angle of SiCl4 is 109.5°
6. It will self-ignite at a temperature above 650 °C
7. SiCl4 is regarded as an irritant to the skin, eye, and the respiratory system
8. Silicon Tetrachloride is a great source of crystalline silicon that is water-soluble.
9. In the early 1980s, the direct production of silicon tetrachloride by the reaction of chlorine on silicon was discontinued all over the world.
10. It is neither explosive nor oxidizing.
Manufacturing of SiCl4
(i) SiCl4 can be prepared by reaction of silicon with chlorine and under irradiation with ultra-violet light
SiHCl3 + Cl2 → SiCl4 + HCl
SiO2 (s) + 2Cl2 (g) → SiCl4 (g) + O2 (g)
(ii) SiCl4 can also be obtained by reaction of silicon carbide with hydrogen chloride.
SiC + 4HCl → SiCl4 + CH4
(iii) Byproduct in the production of zirconium tetrachloride.
ZrSiO 4 + 4C + 4 Cl 2 = ZrCl 4 + SiCl 4 + 4CO
In all the forms, the covalent bonds between Si and Cl are polar due to the greater electronegativity difference between them.
The greater the electronegativity, the greater is the dipole moment
The compound as a whole is non-polar because of the cancellation of dipole moment in the opposite direction.
I hope, this article has helped you to know in detail about the polarity of SiCl4 and other attributes of this compound.
Other Related Questions
Why is SiCl4 a liquid and has low boiling and melting point?
As SiCl4 is a covalent compound, they are held together by weak intermolecular forces. Therefore these molecules require less energy to break their bond.
This can be attained at a very low boiling and melting point.
How does SiCl4 react with water?
Silicon tetrachloride reacts with water to produce orthosilicic acid and hydrogen chloride.
SiCl4 + 4H2O ——> Si(OH)4 + 4HCl
How can it be stored and handled safely?
It can be stored safely in the absence of air as it has no possible action on iron, steel, or the common metal alloys and can be handled using metal equipment without danger.