Carbon Compounds What You Should Know

Carbon compounds are chemical substances that contain carbon atoms bonded to any other element. There are more carbon compounds than for any other element except hydrogen. The majority of these molecules are organic carbon compounds (e.g., benzene, sucrose), although a large number of inorganic carbon compounds also exist (e.g., carbon dioxide). One important characteristic of carbon is catenation, which is the ability to form long chains or polymers. These chains may be linear or can form rings. Types of Chemical Bonds Formed by Carbon Carbon most often forms covalent bonds with other atoms. Carbon forms nonpolar covalent bonds when it bonds to other carbon atoms and polar covalent bonds with nonmetals and metalloids. In some instances, carbon forms ionic bonds. An example is a bond between calcium and carbon in calcium carbide, CaC2. Carbon is usually tetravalent (oxidation state of 4 or -4). However, other oxidation states are known, including 3, 2, 1, 0, -1, -2, and -3. Carbon has even been known to form six bonds, as in hexamethylbenzene. Although the two main ways to classify carbon compounds are as organic or inorganic, there are so many different compounds that they can be further subdivided. Carbon Allotropes Allotropes are different forms of an element. Technically, they are not compounds, although the structures are often called by that name. Important allotropes of carbon include amorphous carbon, diamond, graphite, graphene, and fullerenes. Other allotropes are known. Even though allotropes are all forms of the same element, they have vastly different properties from each other. Organic Compounds Organic compounds were once defined as any carbon compound formed exclusively by a living organism. Now many of these compounds can be synthesized in a lab or have been found distinct from organisms, so the definition has been revised (although not agreed upon). An organic compound must contain at least carbon. Most chemists agree hydrogen must also be present. Even so, the classification of some compounds is disputed. Major classes of organic compounds include (but are not limited to) carbohydrates, lipids, proteins, and nucleic acids. Examples of organic compounds include benzene, toluene, sucrose, and heptane. Inorganic Compounds Inorganic compounds may be found in minerals and other natural sources or may be made in the lab. Examples include carbon oxides (CO and CO2), carbonates (e.g., CaCO3), oxalates (e.g., BaC2O4), carbon sulfides (e.g., carbon disulfide, CS2), carbon-nitrogen compounds (e.g., hydrogen cyanide, HCN), carbon halides, and carboranes. Organometallic Compounds Organometallic compounds contain at least one carbon-metal bond. Examples include tetraethyl lead, ferrocene, and Zeises salt. Carbon Alloys Several alloys contain carbon, including steel and cast iron. Pure metals may be smelted using coke, which causes them to also contain carbon. Examples include aluminum, chromium, and zinc. Names of Carbon Compounds Certain classes of compounds have names that indicate their composition: Carbides: Carbides are binary compounds formed by carbon and another element with a lower electronegativity. Examples include Al4C3, CaC2, SiC, TiC, WC.Carbon Halides: Carbon halides consist of carbon bonded to a halogen. Examples include carbon tetrachloride (CCl4) and carbon tetraiodide (CI4).Carboranes: Carboranes are molecular clusters that contain both carbon and boron atoms. An example is H2C2B10H10. Properties of Carbon Compounds Carbon compounds share certain common characteristics: Most carbon compounds have low reactivity at ordinary temperature but may react vigorously when heat is applied. For example, cellulose in wood is stable at room temperature, yet burns when heated.As a consequence, organic carbon compounds are considered combustible and may be used as fuels. Examples include tar, plant matter, natural gas, oil, and coal. Following combustion, the residue is primarily elemental carbon.Many carbon compounds are nonpolar and exhibit low solubility in water. For this reason, water alone is not sufficient to remove oil or grease.Compounds of carbon and nitrogen often make good explosives. The bonds between the atoms may be unstable and likely to release considerable energy when broken.Compounds containing carbon and nitrogen typically have a distinct and unpleasant odor as liquids. The solid form may be odorless. An example is nylon, which smells until it polymerizes. Uses of Carbon Compounds The uses of carbon compounds are limitless. Life as we know it relies on carbon. Most products contain carbon, including plastics, alloys, and pigments. Fuels and foods are based on carbon.