What is invisible and all around us? It is air. Air is composed of a number of gases, the most abundant of them being nitrogen (78%) and oxygen (21%). The remaining 1% are trace gases, one of which is highly toxic carbon monoxide (CO).
Carbon monoxide is an odorless and colorless gas. It is considered the most abundant air pollutant, by mass. Just like carbon dioxide (CO2), it is also released during the combustion of hydrocarbons, but it requires incomplete combustion (burning in the lack of oxygen).
The chemistry of carbon monoxide is interesting, its single-molecule contains one atom of carbon and one atom of oxygen. It is one of the most studied and questioned compounds in organic chemistry.
But, is carbon monoxide ionic or covalent? CO is a covalent compound, as firstly, it consists of a double covalent bond and a single coordinate covalent bond (in total, 3 covalent bonds), between carbon and oxygen atoms. Secondly, due to a small difference of electronegativities of carbon and oxygen atoms (∆E=1.0), these atoms settle upon sharing of electrons. Since sharing of electrons forms covalent bonds, carbon monoxide is a covalent compound.
Let’s learn more about the types of bonds, the criteria of their formation and bonding in carbon monoxide.
Types of a chemical compound
Based on the interaction between different types of elements present in a compound, there are mainly two types of compounds, i.e. ionic compounds and covalent compounds.
The latter can also be known as metallic compounds or coordinate compounds, depending on the elements present.
An ionic compound is formed when a metal interacts with a nonmetal and forms an ionic bond by losing and gaining electrons (transfer of electrons). For example, NaCl, MgBr2, AlCl3.
When the same types of elements interact with each other (metal-metal or nonmetal-nonmetal or metalloid-nonmetal), a covalent bond is formed and such compounds are known as covalent compounds. Such as CO2, NH3, H2O, SiO2.
Do you know why chemical bonding occurs? Because every atom wants to acquire stability. The stability can be achieved, either by the transfer of electrons (ionic bonding) or by sharing of electrons (covalent bonding). By chemical bonding, an atom completes its octet and reaches the nearest noble gas configuration.
Whenever a bond is formed by sharing of electrons between two atoms, it is known as a covalent bond. There is no loss or individual gain of electrons of one atom. There is a mutual gain of electrons of both atoms, which leads to stability.
Such compounds are known as covalent compounds and the shared pair of electrons, which bind together atoms of two elements are known as “bonding pair of electrons”.
Electronegativity also plays a role in deciding which bond formation will occur. If the electronegativity difference between two elements is less than 2.0, a covalent bond is formed.
For example, in nitric oxide (NO), the electronegativity of N is 3.0 and that of O is 3.5 Hence, ∆E = 0.5. Since this difference is less than 2.0, NO is a covalent compound.
Ionic bonds are formed when one atom loses electrons while another atom gains electrons. There is an overall transfer of electrons from a less electronegative element (donor) to a more electronegative one (acceptor).
This, therefore, leads to the formation of ions (cations and anions) in an ionic compound.
Transfer of electrons can occur only due to a huge difference between the electronegativities of two elements. For a compound to be ionic, the difference must be greater than 2.0
For example, in sodium chloride (NaCl), the electronegativity of Na is 0.9 and that of Cl is 3.1. So, ∆E = 2.2, and sodium chloride is an ionic compound.
Carbon monoxide is also known as carbon oxide or carbonic oxide. It is a toxic gas with no characteristic odor or color. CO has sp hybridized carbon with an overall linear structure (bond angle = 180°).
Carbon monoxide is poisonous when inhaled and highly flammable while in use. Hence, it is a kind of gas that requires utmost precaution while handling.
A major part of this gas, present in the atmosphere, is produced via anthropogenic sources such as the burning of fossil fuels, automobile exhaust, forest fires, etc.
At the industrial level, carbon monoxide is produced by heating powdered zinc with a calcium carbonate mixture. It can also be produced by the reaction between silver nitrate and iodoform.
Apart from toxicity and adverse effects, this gas also has many applications. It is widely used as a reducing agent to form other compounds such as phosgene and aldehydes. It is also used in metallurgical reactions, infrared lasers, and the manufacturing of nickel.
Do you know? Gas stoves, house fires, furnaces, barbecues, kerosene, and gas heaters can also produce carbon monoxide, hence smoke from these must be released outside immediately.
Covalent Bonding in CO (Carbon Monoxide)
Carbon monoxide molecules consist of one atom of carbon with 4 electrons in its outer shell and one atom of oxygen with 6 electrons in its outer shell.
The ground state electronic configurations of carbon and oxygen are as follows:
C (atomic number = 6): 1s2, 2s2 2p2
O (atomic number = 8): 1s2, 2s2 2p4
As we can see, carbon requires 4 more electrons to complete its octet and reach noble gas configuration. Whereas, oxygen requires 2 more electrons to do the same.
The difference between the electronegativities of carbon (E=2.5) and oxygen (E=3.5) is ∆E = 1.0. As this difference is less than 2.0, the bond formed between carbon and oxygen should be covalent.
With one covalent bond, both atoms share one electron each and after sharing, every atom has one extra electron. With the formation of two covalent bonds, the oxygen and carbon atom gets two extra electrons each. With this, the octet of oxygen is completed.
Now, carbon is still in need of 2 more electrons (as it wanted 4 electrons). For this, oxygen contributes one of its lone pairs to carbon through the formation of one coordinate covalent bond.
This is a partially shared bond as electrons are contributed by only one atom but they belong to both atoms now. With this, the octet of carbon is also completed.
Note that, unlike ionic compounds, no ions (cation and anion) are formed in a covalent compound.
Toxicity of Carbon Monoxide
Carbon monoxide is toxic to both health and the environment. When inhaled in large quantities, this gas can react with iron present in the hemoglobin and convert it into carboxyhemoglobin.
This form of hemoglobin has the least affinity for oxygen, which ultimately leads to asphyxiation in the human body. Vital body organs become deprived of oxygen and people experience suffocation. This is referred to as ‘CO poisoning’.
Workers working in mines, people living in highly polluted areas (metro cities, industrial areas) are more prone to CO poisoning.
When released into the environment, carbon monoxide enhances the number of greenhouse gases, which in turn contributes to global warming and climate change.
Do you know? Carbon monoxide is also known as a “silent killer” as it is indetectable i.e. you can’t identify whether the gas is nearby you or not, but when you inhale it, CO can silently end your life.
In this article, we learned about the types of chemical compounds, i.e. ionic and covalent compounds, their bonding based on the type of elements (metals, nonmetals, and metalloids), and the role of electronegativity in determining the nature of bonds.
Further, we looked into detail about carbon monoxide and its covalent structure. We learned that there are three covalent bonds, formed by sharing of electrons, that are present between carbon and oxygen atoms of a CO molecule.
We also saw how carbon monoxide can be toxic when inhaled or when released into the atmosphere. Hence, the utmost care has to be taken while handling it.