Silicon dioxide (SiO2) lewis dot structure, molecular geometry or shape, electron geometry, polar or nonpolar, formal charges, hybridization
SiO2 is the chemical formula for silicon dioxide, preferably known as silica. It is found in different crystalline solids, such as quartz, and in amorphous forms, such as silica gel.
Silica is the primary component of glass making. It is also used as a filtration medium for water treatment, in abrasive materials and as a desiccant.
In this article, you will learn to draw the Lewis dot structure of silicon dioxide (SiO2), its molecular geometry or shape, electron geometry, bond angles, hybridization, formal charges, polarity, etc.
So, without any further delay, dive into the article and start reading!
The Lewis dot structure of silica (SiO2) comprises a silicon (Si) atom at the center. It is double-covalently bonded to two oxygen (O) atoms, one on either side. There is no lone pair of electrons on the central Si-atom; however, each O-atom carries 2 lone pairs in the SiO2 Lewis structure.
You can easily draw the Lewis structure of SiO2 by following the simple steps given below.
Steps for drawing the Lewis dot structure of SiO2
1. Count the total valence electrons present in SiO2
SiO2 consists of two distinct elements, i.e., silicon and oxygen.
Silicon (Si) is present in Group IV A (or 14) of the Periodic Table of Elements. Thus, it has a total of 4 valence electrons in each atom.
In contrast, oxygen (O) is located in Group VI A (or 16), containing 6 valence electrons in each atom.
Total number of valence electrons in silicon = 4
Total number of valence electrons in oxygen = 6
SiO2 comprises 1 Si-atom and 2 O-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of SiO2 = 1(4) + 2(6) = 16 valence electrons.
2. Find the least electronegative atom and place it at the center
By convention, the least electronegative atom out of all those available is chosen as the central atom while drawing the Lewis structure of a molecule.
The least electronegative atom can easily form covalent bonds with other atoms by sharing its electrons.
Among the two types of atoms present in SiO2, silicon (E.N = 1.90) is less electronegative than oxygen (E.N = 3.44).
Hence the Si-atom is placed as the central atom in the SiO2 Lewis structure, while the two O-atoms are placed at the sides, as shown below.
3. Connect the outer atoms with the central atom
In this step, the terminal O-atoms are joined to the central Si-atom using single straight lines.
A straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons.
2(2) = 4 valence electrons used out of the 16 initially available means we are now left with 12 valence electrons.
So let’s see in the next steps where we can place these remaining valence electrons in the SiO2 Lewis structure.
4. Complete the octet of the outer atoms
An O-atom needs a total of 8 valence electrons to gain a full octet configuration.
A Si-O bond represents 2 valence electrons already present around an O-atom.
Therefore, to complete the octets of the two O-atoms in the SiO2 Lewis structure, 3 lone pairs are placed around each, as shown below.
5. Complete the octet of the central atom and convert lone pairs into covalent bonds if necessary
Total valence electrons used till step 4 = 2 single bonds + 2(electrons placed around each O-atom, shown as dots) = 2(2) + 2(6) = 16 valence electrons.
Total valence electrons – electrons used till step 4 = 16 – 16 = 0 valence electrons.
As all 16 valence electrons initially available for drawing the SiO2 Lewis structure are already consumed so there is no lone pair on the central Si-atom.
However, a problem here is that the central Si-atom still has an incomplete octet with only 2 single bonds, i.e., 2(2) = 4 valence electrons surrounding it.
But don’t worry because we can easily solve this problem by converting lone pairs into extra covalent bonds.
A lone pair from each terminal O-atom is converted into an extra covalent bond between the central Si-atom and the respective O-atom,as shown below.
This leads to the formation of two double bonds around the Si-atom, fulfilling its electron deficiency.
As a final step, let’s check the stability of the above Lewis structure by applying the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
Formal charge = [valence electrons- nonbonding electrons- ½ (bonding electrons)].
Now let us use this formula and the Lewis structure obtained in step 5 to determine the formal charges present on the SiO2 bonded atoms.
What is the electron and molecular geometry of SiO2 (Silicon dioxide)?
Silicon dioxide (SiO2) possesses an identical electron and molecular geometry or shape, i.e., linear. There is no lone pair of electrons on the central Si-atom, so no distortion is present in the shape and geometry of the molecule.
Molecular geometry of SiO2
The molecular geometry or shape of silicon dioxide (SiO2) w.r.t the central Si-atom is linear.
The central Si-atom is directly bonded to two O-atoms via double covalent bonds, one on either side. There is no lone pair of electrons on the central Si-atom, so no lone pair-lone pair or lone pair-bond pair electronic repulsions are present in the molecule.
Hence SiO2 occupies an ideal linear shape in which the bonded atoms lie on a single straight line, as shown below.
Electron geometry of SiO2
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 2 electron density regions around the central atom is linear.
In SiO2, the central Si-atom is directly bonded to 2 O-atoms, and it has no lone pair of electrons. This makes a total of 2 electron-density regions surrounding the central Si-atom. As a result, the ideal electron pair geometry of SiO2 is linear.
An easy trick to finding a molecule’s electron and molecular geometry is using the AXN method.
AXN is a simple formula representing the number of bonded atoms and lone pairs on the central atom.
It is used to predict the shape and geometry of a molecule using the VSEPR concept.
AXN notation for SiO2
A in the AXN formula represents the central atom. In SiO2, a silicon (Si) atom is present at the center, so A = Si.
X denotes the atoms bonded to the central atom. In SiO2, two O-atoms are directly bonded to the central Si-atom, so X= 2.
N stands for the lone pairs present on the central atom. As per the Lewis structure of SiO2, the central Si-atom has no lone pair of electrons. Thus, N= 0 for SiO2.
As a result, the AXN generic formula for SiO2 is AX2N0or simply AX2.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX2 generic formula is identical to its electron geometry, i.e., linear, as we already noted down for silicon dioxide (SiO2).
Hybridization of SiO2
The central Si-atom is sp hybridized in SiO2.
The electronic configuration of silicon is 1s2 2s2 2p6 3s2 3p2.
During chemical bonding in SiO2, one of the two 2s electrons of silicon shifts to its empty 2p atomic orbital. Consequently, the half-filled 2s and one of the three 2p orbitals of silicon hybridize to produce two sp hybrid orbitals.
Each sp hybrid orbital possesses a 50% s-character and a 50% p-character, and both contain a single unpaired electron only.
Silicon uses these sp hybrid orbitals to form the Si-O sigma bonds by sp-sp2 orbital overlap on either side of the molecule.
In contrast, the unhybridized p-orbitals of silicon form the Si=O pi bonds by p-p orbital overlap with adjacent O-atoms, as shown below.
Another shortcut to finding the hybridization present in a molecule is using its steric number against the table given below.
The steric number of the Si-atom in SiO2 is 2, so it has sp hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angle of SiO2
The O=Si=O bond angle is exactly equal to 180° due to the linear shape of the silicon dioxide (SiO2) molecule.
Silicon dioxide polarity: Is SiO2 polar or nonpolar?
As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms with an electronegativity difference between 0.4 and 1.6 units.
In SiO2, an extremely high electronegativity difference of exactly 1.54 units is present between a silicon (E.N = 1.90) and an oxygen (E.N = 3.44) atom in each Si=O bond.
The more electronegative oxygen atoms thus gain partial negative (δ–) charges by strongly attracting the bonded electrons from each Si=O bond, while the central Si-atom obtains a partial positive (δ+) charge in SiO2.
However, it is due to the symmetrical linear shape of silicon dioxide that the oppositely-directed Si=O dipole moments get canceled equally.
This leads to a uniform electron cloud distribution in SiO2 and an overall non-polar molecule (net µ =0).
FAQ
How do you draw the Lewis structure for SiO2?
The Lewis dot structure for silicon dioxide (SiO2) displays a total of 16 valence electrons i.e., 16/2 = 8 electron pairs.
Out of the 8 electron pairs, there are 4 bond pairs and 4 lone pairs of electrons.
A silicon (Si) atom at the center is double-covalently bonded to 2 oxygen (O) atoms, one on either side of the SiO2 Lewis structure.
There is no lone pair of electrons on the central Si-atom.
Each terminal O-atom carries 2 lone pairs, respectively.
How many lone pairs and bond pairs do oxygen and silicon have in the SiO2 Lewis structure?
In the Lewis structure of SiO2:
Each oxygen atom has 2 bond pairs and 2 lone pairs.
The central silicon atom has 4 bond pairs and no lone pair of electrons.
How is the molecular shape of SiO2 different from its electron geometry?
The molecular geometry or shape of silicon dioxide (SiO2) is identical to its ideal electron pair geometry, i.e., linear. The central Si-atom is directly bonded to 2 O-atoms, and there is no lone pair of electrons present on it.
Thus, no lone pair-lone pair or lone pair-bond pair electronic repulsions exist. Hence no distortion is witnessed in its shape and/or geometry.
How is the shape of CO2 similar to or different from that of SiO2?
The molecular shape of CO2 is exactly similar to that of SiO2, i.e., linear. To a C-atom at the center, two O-atoms are double-covalently bonded, and there is no lone pair of electrons on the central C-atom.
Hence its molecular shape stays undistorted.
How is the shape of SiCl4 different from that of SiO2?
The molecular shape of SiCl4 is tetrahedral. To a Si-atom at the center, four Cl-atoms are directly attached like four corners of a tetrahedron.
There is no lone pair of electrons present on the central Si-atom, thus no electronic repulsion or distortion is present in the molecule. It is thus different from the linear shape of SiO2.
How is the three-dimensional structure of silica different from the shape of a single silicon dioxide (SiO2) molecule?
The VSEPR shape of a single SiO2 molecule is linear w.r.t the central Si-atom (as discussed in this article).
Contrarily, in the three-dimensional arrangement, a large number of SiO2 molecules are held together via strong intermolecular forces of attraction to form a gain molecular lattice. Here, each Si-atom is single-bonded to 4 adjacent O-atoms tetrahedrally.
The entire ring comprises eight silicon and eight oxygen atoms, placed alternately. Silica solid is composed of many such rings.
The total number of valence electrons available for drawing the silicon dioxide (SiO2) Lewis structure is 16.
SiO2 possesses an identical electron and molecular geometry or shape, i.e., linear.
The central Si-atom is sp hybridized in SiO2.
The O=Si=O bond angle equals 180° in SiO2.
SiO2 is overall non-polar (net µ = 0) as the equal and opposite Si=O dipole moments get canceled uniformly.
Zero or no formal charges present on either of the O-atoms or the central Si-atom ensures the stability of the SiO2 Lewis structure obtained in this article.
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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