Carbon monoxide
A carbon atom and an oxygen atom lock together in a triple bond that measures 112.8 picometers. This connection creates the simplest carbon oxide known to science, yet it carries a molar mass of just 28.0 grams per mole. The gas is slightly less dense than air because its average molar mass sits below the 28.8 grams per mole found in our atmosphere. Scientists observe this molecule vibrating at a frequency of 2143 inverse centimeters, a high pitch compared to the 1700 inverse centimeters typical of organic carbonyls like ketones. The bond strength reaches 1072 kilojoules per mole, making it the strongest chemical bond currently known. Despite oxygen being more electronegative than carbon, the dipole moment points from the negative carbon end toward the positive oxygen end. This counterintuitive polarity results in a small charge distribution where four shared electrons originate from oxygen while only two come from carbon. The ground electronic state remains a singlet with no unpaired electrons, creating a stable structure for industrial use.
Photochemical degradation of plant matter generates an estimated 60 million tons of carbon monoxide every year. Natural sources include volcanoes, forest fires, and bushfires that release the gas into the troposphere. Human activities contribute significantly through incomplete combustion of fossil fuels and biomass burning. Typical concentrations in the Earth's atmosphere hover around 80 parts per billion. In urban areas near properly adjusted gas stoves, levels may rise between 5 and 15 parts per million. During the mid-1970s, exhaust from automobiles in Mexico City reached concentrations between 100 and 200 parts per million. Undiluted warm car exhaust without catalytic converters can contain up to 30,000 to 100,000 parts per million. NASA satellites measure these fluctuations monthly at altitudes of about 12,000 feet. The gas has an average lifetime of one to two months before oxidizing into carbon dioxide and ozone. It acts as a tracer for pollutant plumes moving across continents like South America, Africa, and the Atlantic Ocean. Interstellar space contains this molecule as the second most common diatomic species after hydrogen, detected first by radio telescopes in 1970.
Carbon monoxide poisoning remains the most common type of fatal air poisoning in many countries today. Acute exposure leads to unconsciousness, coma, or death depending on concentration and duration. Chronic exposure to low levels causes lethargy, headaches, nausea, and flu-like symptoms that persist over time. Long-term neurological effects include cognitive decline and behavioral changes that may never fully resolve. Severe cases result in neuropsychological issues and cardiovascular damage that affect daily life. Miners historically called this invisible killer "whitedamp" due to its presence in confined underground areas with poor ventilation. Internal combustion engines and explosives generate high concentrations within coal mines where oxidation occurs slowly. The idiom "canary in the coal mine" originated from early warning systems detecting these toxic fumes before humans could sense them. In developed nations, faulty cooking and heating devices burning fossil fuels are primary sources of indoor emissions. Low- and middle-income countries face higher risks from biomass fuel burning and cigarette smoke indoors. The gas binds tightly to hemoglobin, preventing oxygen transport through the bloodstream and causing tissue suffocation without any color change visible to the naked eye.
Producer gas forms when air passes through a bed of coke at high temperatures inside an oven. This mixture contains mostly carbon monoxide and nitrogen created by the Boudouard reaction above 800 degrees Celsius. Water gas emerges as another source, produced via steam reacting endothermically with carbon to yield hydrogen and carbon monoxide. The Fischer-Tropsch process converts coal or biomass into liquid hydrocarbon fuels using carbon monoxide intermediates. Originally developed during German war efforts to compensate for petroleum shortages, this technology continues today for diesel production. Hydroformylation combines carbon monoxide with alkenes to produce large quantities of aldehydes used in detergents and fragrances. Monsanto researchers developed processes where carbon monoxide reacts with methanol to create acetic acid. World production of phosgene reached 2.74 million tonnes in 1989 alone. Blast furnaces strip oxygen from metal oxides to reduce them to pure metals while forming carbon dioxide. Carbon monoxide generated within these reactors serves as fuel on Cowper stoves and Siemens-Martin furnaces for open hearth steelmaking. Modern electrolysis methods use cerium oxide catalysts to split carbon dioxide without fouling issues.
Scientists first reported carbon monoxide as a normal neurotransmitter in 1993 after decades of research. Heme oxygenase enzymes break down heme derived from hemoproteins like hemoglobin to release the gas naturally. Abnormalities in metabolism link directly to neurodegenerations, hypertension, heart failure, and pathological inflammation. Animal model studies show reduced severity of bacterial sepsis, pancreatitis, hepatic ischemia, colitis, osteoarthritis, lung injury, and neuropathic pain. The molecule acts anti-inflammatory and vasodilatory while encouraging neovascular growth in many tissues. Controlled clinical trials evaluate therapeutic effects against transplant rejection, severe malaria, autoimmunity, and atherosclerosis. Pharmaceutical drug delivery initiatives develop safe administration methods for potential standard-of-care treatments. The human microbiome produces, consumes, and responds to carbon monoxide through proteins such as CooA. Certain bacteria reduce carbon dioxide via carbon monoxide dehydrogenase to power downstream cellular operations. Methanogenic archaea utilize the gas as a nutrient, reducing it to methane using hydrogen for energy.
Humans maintained complex relationships with fire circa 800,000 BC, likely discovering toxicity upon introducing flames into dwellings. Early metallurgy and smelting technologies emerging around 6,000 BC plagued humanity with exposure risks. Aristotle recorded that burning coals produced toxic fumes between 384 and 322 BC. Galen speculated about air composition changes causing harm when inhaled during his lifetime from 129 to 199 AD. Joseph Priestley first synthesized carbon monoxide in 1772 while Carl Wilhelm Scheele isolated it from charcoal in 1773. Torbern Bergman extracted the gas from oxalic acid in 1775 before French chemist Lassone mistakenly identified it as hydrogen in 1776. William Cruickshank finally identified the compound containing carbon and oxygen by 1800. Thomas Beddoes and James Watt recognized its ability to brighten venous blood in 1793. Claude Bernard published memoirs beginning in 1846 stating it prevents arterial blood from becoming venous. Felix Hoppe-Seyler independently confirmed similar conclusions the following year. Hannibal executed Roman prisoners with coal fumes during the Second Punic War, while gas vans operated at Chełmno extermination camps during the Holocaust.
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Common questions
What is the molar mass of carbon monoxide?
Carbon monoxide has a molar mass of 28.0 grams per mole. This value makes the gas slightly less dense than air, which has an average molar mass of 28.8 grams per mole.
When was carbon monoxide first synthesized by scientists?
Joseph Priestley first synthesized carbon monoxide in 1772 while Carl Wilhelm Scheele isolated it from charcoal in 1773. William Cruickshank finally identified the compound containing carbon and oxygen by 1800.
How does carbon monoxide affect human health during exposure?
Acute exposure to carbon monoxide leads to unconsciousness, coma, or death depending on concentration and duration. Chronic exposure causes lethargy, headaches, nausea, and flu-like symptoms that persist over time along with long-term neurological effects.
Where can high concentrations of carbon monoxide be found in urban areas?
In urban areas near properly adjusted gas stoves, levels may rise between 5 and 15 parts per million. During the mid-1970s, exhaust from automobiles in Mexico City reached concentrations between 100 and 200 parts per million.
Why is carbon monoxide considered a strong chemical bond?
The bond strength reaches 1072 kilojoules per mole, making it the strongest chemical bond currently known. This connection creates the simplest carbon oxide known to science yet carries significant stability for industrial use.