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Gaffer Variety:
Elements 7 SN2 009:
By Willie Gaffer:
Carbon (C) is a very abundant nonmetallic element that occurs in many inorganic and in all organic compounds. This element will be of huge importance to me as it is one of the two elements of carbon dioxide (CO2). CO2 is one compound we will have to deal with. It is a major constituent of automobile exhaust and my goal is to change that situation. The atomic number of carbon is 6 and the atomic weight is 12.01115. This stuff sublimates at temperatures above 3,500°C and the boiling point is 4,827°C. It has several specific gravities depending on the form we find it in. For amorphous carbon is 1.8 to 2.1. For diamond it is 3.15 to 3.53. Carbon also has variable valences of 2, 3, and 4.
Carbon occurs freely in almost pure form as graphite and diamond. It is also a ingredient of coal, limestone, and petroleum. It can self-bond to form very many important molecules. Carbon, is the underlying element in living organisms. It is also important to many industries. A carbon atom can chemically combine with atoms of other elements, as well as with other carbon atoms, to form many molecules. In fact carbon can form more compounds can any other element except hydrogen.
Carbon is present in all substances known as organic compounds. Originally, scientists used the term organic compounds for materials that could only be obtained from living or dead organisms. Today chemists consider nearly any compound that contains carbon to be organic, whether they obtain it from organisms or synthesize it in a laboratory or in factories. Compounds that do not contain carbon are called inorganic compounds.
When we think about our modern life, it is difficult to think of anything we use that does not contain compounds of carbon. Thee include sugars, proteins, fats, (DNA) for sure and, many of the materials that we use in everyday life. Think of clothing , wood, and plastics. I have already pointed out that we also burn fossil fuels, including gasoline, natural gas, and coal, which are compounds of carbon. In addition, we use organic compounds as pesticides and medicines, and the foods we eat are carbon compounds.
Of all the elements, carbon is the only one suitable for building the variety of molecules necessary to sustain life. Carbon atoms can attach to each other to form chains, rings, or a crystal mesh. The chains may be thousands of carbon atoms long and either linear or branched, and the rings usually contain from three to six carbon atoms. Most organic compounds contain many carbon-hydrogen bonds. Some of the other elements that bond to carbon include oxygen, nitrogen, fluorine, chlorine, bromine, iodine, sulfur, and phosphorus.
Carbon has three naturally occurring isotopes. The isotopes of carbon are carbon-12 with six neutrons. This makes up 98.89 of all carbon atoms and serves as the standard for the atomic mass scale, carbon-13 with seven neutrons. This is the only magnetic isotope, making it very important for structural studies of compounds containing carbon. Last is carbon-14 with eight neutrons. This is caused by cosmic rays bombarding the atmosphere. Carbon-14 is radioactive, with a half-life of 5760 years. The amount of carbon-14 remaining in historical artifacts can be used to estimate their age.
Carbon-14 dating is a technique for discovering the age of ancient fossils. All living organisms absorb C-14, an unstable form of the element carbon that slowly decays into nitrogen-14 (N-14). During its lifetime, an organism continually replenishes its supply of C-14 by breathing and eating. After the organism dies and becomes a fossil, C-14 decays without being replaced. Scientists know the rate at which C-14 decays and can detect the electrons that C-14 emits as it decays.
Carbon atoms have two electrons in their inner shell making it full. There are four valence electrons in the outer shell. Since this outer electron shell can hold eight electrons, carbon atoms can form four covalent bonds with other atoms. Recall that a covalent bond is a bond formed when two atoms share a pair of electrons. When two atoms share one pair of electrons, the covalent bond is called a sigma bond and it holds the electrons tightly between the two atoms. One pair of shared electrons is also called a single bond. When two atoms share two pairs of electrons (creating a double bond), the first shared pair forms a sigma bond, while the second pair forms a pi bond. In the pi bond the electrons are more easily broken away. When two atoms share three pairs of electrons (creating a triple bond), two of the bonds are pi bonds.
Carbon atoms can bond together in chains, rings, and mesh-like networks. If a carbon atom bonds with four identical atoms, those atoms will be equally distant from each other—at the tips of an imaginary tetrahedron, or a pyramid with a triangular base. Any two of the bonds form an angle of 109.5° when carbon is in a tetrahedral form. Atoms of the element carbon can link together in several ways to form substances with very different properties.
As we noticed, carbon is used by all living organisms so it continuously circulates in our ecosystem. In the atmosphere, it exists as colorless, odorless carbon dioxide gas, which is used by plants in the process of photosynthesis. Animals acquire the carbon stored in plant tissue when they eat and exhale carbon dioxide as a by-product of metabolism.
Carbon is widely distributed in nature and the universe. We have already discussed how carbon occurs as a pure element and in countless organic compounds on Earth. But carbon also abounds in the Sun, stars, comets, and in the atmospheres of most planets. The atmosphere of Mars is mostly carbon dioxide (carbon bonded with two oxygen atoms, or CO2). Earth’s atmosphere contains only 0.03 percent CO2. Like virtually all atoms, carbon atoms are made in the interior of stars during a supernova, an explosion of a star that emits vast amounts of energy. These explosions build atoms in thermonuclear reactions. Hydrogen atoms fuse together into a helium atom, then helium atoms fuse into carbon. Carbon atoms can then fuse with helium into oxygen.
This is just a surface look a carbon. As I said, it will be of ongoing interest to my investigation of the problems we currently face.