Is SiO2 a polar or nonpolar substance?

Silicon Silicon dioxide, sometimes known as silica, is the oxide of Silicon. It’s also known by other names, such as quartz and dioxo silane. It comes in crystalline and amorphous varieties.

Various polymorphs have different melting points. It’s abundant in the earth’s crust and even in the green leafy crops we eat. SiO2 is the most common type of glass used in windows and tableware. It’s odourless and tasteless, and it’s white or colourless.

In this post, we will analyse the polarity of SiO2 and the factors that influence it. We’ll also look at the differences between polar and non-polar molecules, as well as silicon dioxide’s features, applications, and risks.

Is SiO2 polar or nonpolar, then? Because of its symmetrical and linear form, SiO2 is a non-polar molecule. The bonds in the molecule are polar because the oxygen atom is more electronegative than the silicon atom, but the dipoles of both bonds in SiO2 balance out due to the linear and opposite orientations of both links. As a result, the net dipole moment is zero, and SiO2 is non-polar.

Silicon is in the +4 oxidation state, while O is in the +2 oxidation state. O is a non-metal, while Si is a metalloid. As a result, the bond between them is covalent. 60.084 grammes is the molar mass.

Polar and Non-Polar Molecules: What’s the Difference?

Basis Polar molecules Non-polar molecules
Charge separation Non-uniform Uniform
Net dipole moment Non zero Zero
Intermolecular forces Stronger intermolecular forces Relatively weaker  intermolecular forces
Electricity conduction Conducts electricity in solution It does not conduct electricity
Melting and boiling  pointRelatively higher Relatively lower
Polar bonds Present Can be present or absent
Symmetry Not symmetrical Generally symmetrical
Example H2O, NH3, SO2, etc. CO2, BF3, SF6, etc.

I’ve also written on BF3 in the context of polar compounds. Take a look at BF3’s polarity.

Factors Affecting a Compound’s Polarity

Polar molecules are those that have both a positive and a negative end, which can be induced or natural.

Because this definition can be unclear at times, the dipole moment idea for identifying polarity is more dependable.

  1. Dipole moment (): The product of the charge and the distance between the two poles of a dipole is the dipole moment ().

Debye is the SI unit for it. It occurs as a result of a variation in electronegativity.

(Cm) = Q (C) * r r r r r r r r r r r r (m)

where the dipole moment is, and

The magnitude of charges is denoted by Q, and

The separation distance between two charges is denoted by r.

  1. Charge Separation: The dipole moment is determined by the charge and charge separation, as shown in the formula.

Induction can be used to create a partial charge. The charge separation and dipole moment have a linear relationship.

Charge distribution is non-uniform for polar molecules and uniform for non-polar ones. SiH4 is an example of a nonpolar chemical. Check see the article on SiH4 polarity.

  1. Electronegativity Difference: As they draw the shared pair of electrons towards themselves, more electronegative atoms develop a partial negative charge, while less electronegative atoms develop a partial positive charge.

As a result, the size of these charges is determined by the difference in electronegativities. The greater the difference, the greater the dipole moment.

As a result, the difference in electronegativity between two atoms is a significant determinant in the creation of dipole moment.

  1. Molecule Geometry- This is also important for molecules with more than two atoms. Diatomic molecules are always linear, and a polar bond, and hence a polar molecule, is formed simply by a difference in electronegativity.

The vector sum of bonds is taken into account for larger molecules. The form would have been twisted and the net dipole moment would not have been zero if core atom Si had lone pairs (hypothetical).

The dipole moment is cancelled by the symmetric arrangement.

Why is SiO2 a non-polar material?

The existence or absence of a net dipole moment determines a compound’s polarity.

The dipole moment, as we all know, is a vector quantity, meaning it is impacted by both magnitude and direction. Because the electronegativity of silicon and oxygen is 1.9 and 3.44, respectively, the bonds are polar and covalent.

If the electronegativity difference is greater than 2, the compound is ionic, and if it is less than 2, it is covalent. The difference is 1.54 over here, indicating that SiO2 is a covalent molecule (the difference is less than 2).

Dipole moment vectors are directed from the less electronegative atom to the more electronegative atom.

As a result, the vectors in SiO2 are in the opposite direction, and the associated dipole moment is zero due to the symmetry of molecular geometry.

SiO2 Molecular Structure

The formula is simple. SiO2 is an empirical formula that does not accurately reflect the structure. It’s a solid made up of macromolecular molecules.

• SiO2 belongs to the silicate family of chemicals. A SiO4 tetrahedral molecule is the fundamental unit of silicates.

• In SiO2, all four O-atoms of SiO4 are shared with another Si, forming Si-O-Si bridges, as seen in the picture.

• Because of the symmetry, the dipole moments of the bonds cancel out each other in this molecular structure, and the molecule as a whole is non-polar.

• Thus, at first glance, the Lewis structure of SiO2 is sufficient to explain a variety of features, but this is not the case.

• Si-O bonds are more powerful than Si=O bonds, and double bonds are uncommon.

• The molecular solid’s Lewis structure is depicted.

• This basic structure of SiO4 is present in all crystalline forms of silica, and those polymorphs (one compound appearing in numerous crystalline forms) are interconvertible according to the flowchart below.

• Quartz is the most stable silica polymorph. Quartz is a crystalline material, while quartz glass is amorphous.

• As the liquid silica cools, it condenses into an amorphous glass with a random SiO4 structure (and hence non-crystalline). Because it meets the necessary criteria, SiO2 is one of the oxides that can create Glass.

Properties of SiO4

  1. Materials: sand, quartz purification, and food (green beans, bananas, brown rice, etc.)
  2. Preparation- SiO2 is made by exposing elemental Si to oxygen. The wet approach, as given in the equation below, is used to make amorphous silica in laboratories.

3SiO2 + Na2SO4 + H2O = Na2Si3O7 + H2SO4 + H2O

  1. Density (g cm-3): 2.648 (much more than water)
  2. Melting and boiling points- Due to silica’s strong network and high stability, the temperatures required for boiling (1713°C) and melting (2950°C) are relatively high.
  3. Solubility – “What goes around comes around.” In polar and non-polar solvents, polar and non-polar molecules can be dissolved, respectively.

Under normal circumstances, SiO2 is not soluble in water. Because the network is so robust, bonds do not break when submerged in water.

  1. HF Reaction – HF is a powerful mineral acid that can dissolve Si-O bonds. It has the ability to dissolve silica.

Gravimetric analysis with HF is used to estimate the amount of silica in a sample.

SiF4 + 2H2O = SiO2 + 4HF

2H2SiF6 + H4SiO4 = 3SiF4 + 4H2O

  1. Conducting characteristics — Because of its high dielectric strength, silica is utilised as an insulator in microelectronics. It’s a very stable substance.
  2. Silica nanoparticles are created and, due to their non-toxic nature, are particularly effective as a transport mechanism for genes, plasmid cells, and other genetic material.

Uses of SiO2

One of the most abundant oxides on the earth is silicon dioxide. It can be found in a variety of forms in nature and is also quite useful in industry. It can be found in:

  1. Pharmaceuticals – sedatives, pills, etc.
  2. Flavor enhancer, anti-caking agent in the food industry (its function is to make powdered ingredients less sticky) malt beverage defoaming, conditioning, fining, and chill proofing agents, packaging material, filtration
  3. Construction – producing concrete, cement, enamel, ceramics, and glass, among other things.
  4. Other applications include hydraulic fracturing, the manufacturing of elemental Silicon, and toothpaste additives. Microelectronics is the fifth item on the list.
  5. Telecommunications optical fibres
  6. Chemical industry – adhesives, adsorbents, corrosion inhibitors, sealants, porcelain, paint, and colour additives are all manufactured in this industry.
  7. Dementia is less likely when there is silica in the water. Silica supplements are used to treat concerns such as weak bones, heart disease, hair loss, and digestive problems.

Interesting fact

It’s not uncommon for ancient window glass to become milky.

One of the key components of the glass is silica (quartz polymorph). It becomes heated up from constant contact to the sun, and when exposed to a chilly atmosphere at night, it converts to a partially crystalline state, giving it a milky appearance.

Conclusion

• SiO2 is a macromolecular solid whose basic unit is SiO4. It’s a simple molecule that comes in a variety of crystalline and amorphous forms, each with its own set of features.

• Because of the electronegativity difference between Si and O, the covalent bonds between them are polar in all forms.

• Due to the cancellation of the dipole moment in the opposite direction, the compound as a whole is non-polar.

• SiO2 is a valuable and stable compound that has a wide range of applications. I hope you enjoyed learning about silica chemistry!

Read more: Is CH2F2 a polar or nonpolar substance?

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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