Is SiO2 an Ionic or a Covalent Compound?

Metals, nonmetals, and metalloids are the three major categories of elements found in the periodic table. Every element seeks stability, which it achieves by bonding. Chemical bonds can be ionic, covalent, hydrogen bonds, or Vander Waal bonds, depending on the sorts of atoms interacting or connecting with each other.

Because of its bonding properties, SiO2 is frequently misunderstood. Silicon dioxide, sometimes known as “quartz” or “silica,” is a crystalline network solid formed primarily of polar covalent interactions between the elements silicon and oxygen. The earth’s crust contains a lot of these elements in the form of silicon dioxide.

Around 59 percent of the earth’s crust is made up of silicon dioxide. It’s most common in sands and rocks like granite. From acting as a medication addition to anti-caking agents in dietary supplements, it plays a vital role in our daily lives.

Is silicon dioxide, on the other hand, ionic or covalent? Silicon dioxide is a polar covalent compound in which each silicon atom in a crystal is covalently connected with four oxygen atoms and each oxygen atom is covalently bonded with two silicon atoms. Its covalent nature is due to a minor discrepancy of 1.5 between the electronegativities of silicon (E=1.9) and oxygen (E=1.5) (3.4). This difference must be more than 2.0 for a compound to be ionic. As a result, silica behaves similarly to a covalent molecule.

Let’s take a closer look at the ionic compounds, covalent compounds, and chemistry of silicon dioxide.

What is the definition of a covalent compound?

Covalent compounds are those in which electrons are shared between two atoms to form a covalent bond.

These “bonding pairs of electrons” are shared pairs of electrons that unite two atoms and are present in the valence shell (outermost shell) of atoms because they form bonds.

Covalent bonds are formed when the electronegativities of the involved atoms are almost identical. Because neither of them is powerful enough to pull the common pair of electrons towards themselves.

The difference between electronegativities must be less than 1.7 to produce a pure covalent bond.

Because one of the atoms has a little charge dominance, the molecule is polar covalent if the difference is between 1.7 and 2.0.

Case 1: When the valence electrons of two nonmetals are shared. Nitrogen monoxide (NO), for example, is made up of two nonmetals, nitrogen and oxygen, which have equal electronegativities.

Case 2: When the valence electrons of a metalloid and a nonmetal are shared. Silicon dioxide, for example (SiO2).

What is the definition of an ionic compound?

Ionic compounds are those in which one atom loses an electron and another gains an electron, and an ionic bond is the sort of link created between two atoms.

In contrast to covalent connections, ionic bonds do not share electrons.

Ionic bonds are formed when the electronegativities of the involved atoms differ enough that atoms with higher electronegativities can attract the valence electrons of atoms with lower electronegativities.

Ionic bonding result in the gain of electrons by one atom (high E) and the loss of electrons by another atom (low E).

A nonmetal and a metal create such bonds, with the metal acting as an electron donor and the nonmetal acting as an electron acceptor. The difference in electronegativity between them is more than 2.0. Sodium chloride, for example (NaCl).

Bonding between ions

Do you have any idea? The need for a complete octet in a molecule derives from the need for all atoms in the universe to remain stable.

Some molecules choose the covalent mode, which involves sharing electrons, while others choose the ionic mode, which involves removing or gaining electrons.

What causes Silicon Dioxide to form?

Silicon dioxide, commonly known as “quartz,” “silica,” “Kalii bromidum,” or “silicic oxide,” is a network solid made up of covalent bonds between silicon and oxygen, two of the most prevalent elements on the planet.

When isolated silicon is exposed to a large amount of oxygen, silicon dioxide is generated.

Each silicon atom in a crystal of silicon dioxide is covalently connected with four oxygen atoms, and each oxygen atom is covalently bonded with two silicon atoms, giving a tetrahedral structure as illustrated below.

Because the arrangement and orientation of atoms in the network are random, silicon dioxide is usually an amorphous crystalline solid. Aside from its amorphous structure, silicon dioxide comes in a variety of crystalline forms (polymorphs).

Silicon dioxide is found naturally in sand and rocks, and it is extracted by mining. Continuous acidification of a sodium silicate solution yields amorphous silicon dioxide at the industrial level.

Trisilicate and sulphuric acid are employed in the reaction described below.

Na2Si3O7   +   H2SO4   —–>   3SiO2   +    Na2SO4   +    H2O

What Makes Silicon Dioxide Covalent?

The electronegativities of silicon and oxygen differ by 1.5, allowing it to act as a polar covalent solid and preventing it from imparting ionic behaviour.

Because the oxygen atom, grouped in a tetrahedron surrounding silicon, pulls the shared pair of electrons more strongly than the silicon, it is called a “polar covalent” compound.

However, because the electrons are still shared and there is no loss or gain of electrons, it is not considered an ionic compound.

Silicon Dioxide’s Characteristics

Silicon dioxide is a colourless, odourless, and tasteless substance.

In its crystalline or amorphous powdered state, it is translucent to grey in colour.

Silicon dioxide has a molecular weight of 60.08 grammes per mol and a density of 2.648 grammes per cubic centimetre.

Because of its covalent network structure, silicon dioxide is extremely hard. It has a melting point of around 1,610 °C and a boiling point of approximately 2,230 °C. Many of you may be wondering if silicon melts. Here’s the link to the article I wrote about silicone melting.

Silicon dioxide is almost insoluble in water due to its bulky size and massive covalent structure.

Because it is a covalent molecule, it does not conduct electricity.

Silicon Dioxide’s Applications

Silicon dioxide has a wide range of applications, from natural to industrial. The following are some of the most common applications for silicon dioxide:

Around 59 percent of the Earth’s crust is silicon dioxide. It is also a major component of sandstone and can be found naturally in beach sands.

It is commonly used to make concrete in construction projects.

It’s utilised in a variety of medications as a sedative and as an ingredient in pharmaceutical tablets.

It’s commonly used in food supplements as an anti-caking agent to keep powdered ingredients from adhering together.

Because of its conductivity, it is one of the most commonly utilised metals in solar panels. Read an intriguing article about silicon conductivity that I wrote.

In the beverage sector, silicon dioxide is used as a fining agent in the production of juices, beer, and wine.

It is a plaque remover that is added to toothpaste.

In addition, silicon dioxide is utilised in the manufacture of glass.

Is Silicon Dioxide a Toxic Substance?

When taken orally, silicon dioxide is completely non-toxic. While playing, children frequently eat sand and soil, which are high in silica, but this does not impair their health.

Workers and labourers in mines and caves, on the other hand, are susceptible to silica dust. Inhaling fine silica dust particles can cause bronchitis, silicosis, and possibly lung cancer if exposed for lengthy periods of time.

This is because fine silica dust particles accumulate in the lungs and reduce the surface area available for breathing. They can irritate lung tissue and induce internal haemorrhage when deposited in high numbers. In extreme cases, such persons can cough up blood.

As a result, miners must wear specialised masks with respirators at all times.

Covalent and ionic substances have different physical characteristics.

Ionic and covalent compounds have different characteristics and may be identified easily due to the difference in bonding mechanisms. The following are some of these characteristics:

Ionic compounds can only exist in a solid state under normal room conditions, whereas covalent compounds can exist in a solid, liquid, or gas state.

Ionic chemicals can transmit electricity when dissolved in water due to the presence of free ions. Covalent compounds, on the other hand, do not conduct electricity in any condition.

Ionic compounds have greater melting and boiling temperatures than covalent compounds because they can exist in a crystalline structure that is extremely stable.


In this post, we looked at the many sorts of elements, as well as the different types of bonds that make covalent and ionic compounds, and then we formed them using electronegativity differences between atoms.

We investigated the fact that silicon dioxide is a polar covalent compound, not an ionic one, because the electronegativities of silicon and oxygen atoms differ by 1.5.

We also looked into the tetrahedral structure, physical properties, and applications of silicon dioxide. We discovered that while silicon dioxide is harmless when ingested orally, it is exceedingly dangerous when inhaled in large quantities.

Good luck with your studies!

Read more: Geometry, Hybridization, and Polarity of SeF6 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.


Please enter your comment!
Please enter your name here

Read More