Carbon monoxide (CO) Lewis structure, molecular
geometry or shape, electron geometry, bond angle, hybridization, polar or nonpolar
Carbon monoxide, represented by the molecular formula CO (molar mass = 28.01 g/mol), is a colorless, odorless, highly toxic gas. It is produced by the incomplete combustion of carbon-containing compounds.
CO is highly flammable. Therefore, it is used to produce synthetic gas, which in turn is used as a commercial fuel.
In this article, you will learn how to draw the Lewis dot structure of carbon monoxide (CO). Furthermore, we will also discuss important information such as the molecular geometry or shape, electron geometry, bond angle, formal charges, hybridization and polarity of carbon monoxide (CO).
So, come along and learn chemistry in the most fun way possible!
How to draw lewis structure of CO (Carbon monoxide)?
The Lewis structure of carbon monoxide (CO) consists of only two atoms, i.e., a carbon (C) atom and an oxygen (O) atom, triple covalently bonded to each other. Both the bonded atoms carry 1 lone pair of electrons each.
So, drawing the CO Lewis structure is super easy. Come along by following the simple steps given below and draw the carbon monoxide Lewis dot structure with us.
Steps for drawing the Lewis dot structure of CO
1. Count the total valence electrons present in CO
In the first step of drawing the Lewis structure of a molecule, you need to count the total valence electrons present in it.
The valence electrons of an elemental atom can be determined from its group number.
CO is composed of only two elemental atoms. Carbon (C) is present in Group IV A (or 14) of the Periodic Table of Elements, meaning it has 4 valence electrons. In contrast, Oxygen (O) is present in Group VIA (or 16). Each O-atom thus has a total of 6 valence electrons.
Total number of valence electrons in carbon = 4
Total number of valence electrons in oxygen = 6
The CO molecule comprises 1 C-atom and 1 O-atom only.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of CO = 1(4) + 1(6) = 10 valence electrons.
2. Choose the central atom
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.
In carbon monoxide, carbon (E.N = 2.55) is less electronegative than oxygen (E.N = 3.44), so it is chosen as the central atom.
3. Connect the outer atom with the central atom
Only an O-atom is the outer atom in the Lewis structure drawn to this step. So the O-atom is joined to the central C-atom using a single straight line.
The straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons. This implies that 2 valence electrons are already consumed out of the 10 initially available in drawing the CO Lewis structure.
4. Complete the octet of the outer atom
The outer O-atom needs a total of 8 valence electrons in order to achieve a complete octet electronic configuration. A C-O bond represents 2 valence electrons only. So 8- 2 = 6 valence electrons are placed as 3 lone pairs around the O-atom, 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 = 1 C-O single bond + electrons placed around the O-atom, shown as dots =1(2) + 6 = 8 valence electrons.
Total valence electrons – electrons used till step 4 = 10 – 8 = 2 valence electrons.
These 2 valence electrons are placed as a lone pair on the central atom, i.e., the C-atom. But this C-atom still possesses an incomplete octet as only 4 valence electrons are placed around it.
So to complete its octet, 2 of the 3 lone pairs on the outer O-atom are converted into extra covalent bonds between the C-atom and the O-atom.
As all 10 valence electrons initially available are consumed, also both the bonded atoms now have a complete octet, so in the next step, we need to check the stability of the Lewis dot structure obtained above.
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 CO-bonded atoms.
The +1 formal charge of oxygen cancels with a -1 charge of carbon to yield an overall zero formal charge on the carbon monoxide molecule.
Thus, the structure obtained below is stable and a correct Lewis representation of CO.
You may also note that the following resonance structures are possible for representing the CO molecule.
Structure 2 is the most important resonance form. In contrast, structure 1 (the carbenic form) is the least stable and most reactive, as the C-atom has an incomplete octet in it.
Now that we know everything about the Lewis structure of CO let’s move ahead and discuss some other interesting facts.
What are the electron and molecular geometry of CO (Carbon monoxide)?
The carbon monoxide (CO) molecule possesses an identical electron and molecular geometry or shape, i.e., linear. There are 2 electron density regions surrounding the central C-atom in CO, i.e., a bond pair and a lone pair.
However, the lone pair does not disturb the overall geometry and orientation of the molecule.
Molecular geometry of CO
The molecular geometry or shape of carbon monoxide (CO) is linear.
The C-atom and O-atom are triple covalently bonded to each other, and both possess a lone pair of electrons. An equal number of lone pairs on either side of the molecule leads to a symmetrical shape and molecular geometry.
The lone pair-bond pair repulsions are reduced to zero. Therefore, CO is a linear molecule, as shown below.
Electron geometry of CO
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 CO, there is 1 triple bond and 1 lone pair surrounding the central carbon atom, making a total of 2 electron density regions. Hence, its electron geometry is also 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 CO molecule
A in the AXN formula represents the central atom. In the CO molecule, a carbon (C) atom is present at the center, so A = C.
X denotes the atoms bonded to the central atom. In CO, only an O-atom is bonded to the carbon atom. So X = 1 for CO.
N stands for the lone pairs present on the central atom. As per the Lewis structure of CO, the central C-atom carries 1 lone pair of electrons. Thus, N= 1 for CO.
As a result, the AXN generic formula for CO is AX1N1or simply AXN.
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 AXN generic formula is identical to its electron pair geometry, i.e., linear, as we already noted down for carbon monoxide (CO).
Hybridization of CO
Both the C-atom and the O-atom are sp hybridized in the carbon monoxide molecule.
The electronic configuration of carbon is 1s2 2s2 2p2, while that of oxygen is 1s2 2s2 2p4.
During chemical bonding, the 2s atomic orbital of carbon hybridizes with its half-filled 2p orbital to produce two sp hybrid orbitals. Each sp hybrid orbital possesses a 50% s-character and a 50% p-character.
One of the two sp hybrid orbitals contains lone pair of electrons, while the other half-filled sp hybrid orbital forms the C-O sigma bond via sp-sp overlap.
On the other hand, the unhybridized p orbitals of carbon form the required pi-bonds with the p-orbitals of the adjacent oxygen atom, as shown below.
Another shortcut to finding the hybridization present in a molecule is using its steric number against the table below. The steric number of the C-atom in CO is 2, so it has sp hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angle of CO
The carbon and oxygen atoms lie on a perfectly straight line in CO, forming a bond angle of 180°. The C≡O bond length in carbon monoxide is 113 pm.
A high electronegativity difference of 0.89 units exists between the triple-covalently bonded carbon (E.N = 2.55) and oxygen (E.N =3.44) atoms in carbon monoxide (CO).
Oxygen being strongly electronegative, attracts the C≡O bonded electrons toward itself to a greater extent. The C-atom thus gains a partial positive (δ+) charge while the O-atom obtains a partial negative (δ–) charge.
The charged electron cloud stays non-uniformly distributed between the two bonded atoms as the C≡O dipole moment stays uncancelled even in its linear shape.
Furthermore, the polar nature of CO makes it capable of forming dipole-dipole interactions with other polar molecules, such as water, in which CO is freely soluble.
Carbon monoxide dissolves in water to form carbonic acid (H2CO3).
The Lewis dot structure of carbon monoxide (CO) displays a total of 10 valence electrons.
A C-atom is triple covalently bonded to an O-atom.
Both atoms possess 1 lone pair of electrons each.
How many lone pairs and bond pairs are there in the Lewis structure of CO?
The Lewis structure of CO possesses a total of 2 lone pairs and 3 bond pairs, respectively. 1 lone pair is present on the C-atom and 1 on the O-atom. The triple covalent bond between C and O atoms contains a total of 3 bond pairs.
2 lone pairs + 3 bond pairs = 5 electron pairs in CO.
What is the shape of the carbon monoxide (CO) molecule?
CO possesses a symmetrical, planar linear shape and molecular geometry.
Why is the shape of CO identical to its ideal electron pair geometry even though there are lone pairs present?
Both the bonded atoms possess an equal number of lone pairs, i.e., 1. One lone pair of electrons is situated on either side of the molecule.
This leads to maximum separation and, thus, minimum repulsions between the 2 lone pairs. Also, the lone pair-bond pair repulsions are negligible.
Thus, there is no distortion in the shape and geometry of CO, and it possesses an identical linear shape and electron geometry.
How is the shape of CO different from that of CO2?
Both CO and CO2 are linear molecules.
CO consists of only 2 atoms, maximally separated from each other via a triple covalent bond. Thus it possesses a symmetrical, linear shape.
In contrast, 2 O-atoms are double covalently bonded to the central C-atom in CO2. There is no lone pair of electrons on the central C-atom in CO2 thus, no lone pair-lone pair or lone pair-bond pair electronic repulsions exist in the molecule.
In CO32-, three oxygen (O) atoms are bonded to the central C-atom via single and double covalent bonds. There is no lone pair of electrons on the central C-atom; thus, no distortion is present in the shape and geometry of the molecular ion.
Hence, it occupies a symmetrical trigonal planar shape different from the linear CO molecule.
Why is CO a polar molecule despite its symmetrical linear shape?
The CO molecule possesses only 1 polar covalent bond, i.e., C≡O. There are no other bonds in competition.
Thus, the dipole moment of the C≡O bond stays uncancelled even in the linear shape. Consequently, CO is a polar molecule overall (net µ > 0).
The total number of valence electrons available for drawing the CO Lewis structure is 10.
The carbon monoxide (CO) molecule possesses an identical electron and molecular geometry or shape, i.e., linear.
Both the C-atom and the O-atom are sp hybridized in CO.
The C-atom and O-atom lie on a straight line, forming a mutual bond angle of 180° in CO.
CO is a polar molecule (net µ > 0) as the more electronegative O-atom pulls the C≡O shared electron cloud away from the C-atom.
In the most stable Lewis representation of CO, -1 and +1 formal charges are present on the adjacent carbon and oxygen atoms, respectively. However, +1 cancels with -1 to yield an overall formal charge of 0 on the carbon monoxide molecule.
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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The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AXN generic formula is identical to its electron pair geometry, i.e., linear, as we already noted down for carbon monoxide (CO). 
