Compounds are formed from simpler substances by chemical reaction. Some compounds can be formed directly from their constituent elements, e.g., water from hydrogen and oxygen: 2H2 + O2 → 2H2O. Other compounds are formed by reaction of an element with another compound; e.g., sodium hydroxide (NaOH) is formed (and hydrogen gas released) by the reaction of sodium metal with water: 2Na + 2H2O → 2NaOH + H2↑. Compounds are also made by reaction of other compounds; e.g., sodium hydroxide reacts with hydrogen chloride (HCl) to form sodium chloride and water: HCl + NaOH → NaCl + H2O. Complex molecules such as proteins are formed by a series of reactions involving elements and simple compounds.
Compounds can be decomposed by chemical means into elements or simpler compounds. Water is broken down into hydrogen and oxygen by electrolysis. Candle wax, a mixture of hydrocarbons, is changed in the candle flame by combustion (with oxygen) to a mixture of the simpler compounds carbon dioxide (CO2) and water. Life is based on numerous reactions in which energy is stored and released as compounds are produced and decomposed.
A compound has unique properties that are distinct from the properties of its elemental constituents. One familiar chemical compound is water, a liquid that is nonflammable and does not support combustion. It is composed of two elements: hydrogen, an extremely flammable gas, and oxygen, a gas that supports combustion. A compound differs from a mixture in that the components of a mixture retain their own properties and may be present in many different proportions. The components of a mixture are not chemically combined; they can be separated by physical means. A mixture of hydrogen and oxygen gases is still a gas and can be separated by physical methods. If the mixture is ignited, however, the two gases undergo a rapid chemical combination to form water. Although the hydrogen and oxygen can occur in any proportion in a mixture of gases, they are always combined in the exact proportion of two atoms of hydrogen to one atom of oxygen when combined in the compound water. Another familiar compound is sodium chloride (common salt). It is composed of the silvery metal sodium and the greenish poisonous gas chlorine combined in the proportion of one atom of sodium to one atom of chlorine.Molecular and Ionic Compounds
Water is a molecular compound; it is made up of electrically neutral molecules, each containing a fixed number of atoms. Sodium chloride is an ionic compound; it is made up of electrically charged ions that are present in fixed proportions and are arranged in a regular, geometric pattern (called crystalline structure) but are not grouped into molecules. The atoms in a compound are held together by chemical bonding (see chemical bond).
Any member of a class of substances containing at least one metal-to-carbon bond in which the carbon is part of an organic group. Most organometallic compounds are solids, although some are liquids and others are gases. While some organometallic compounds are stable, those containing electropositive elements, such as lithium, sodium, or aluminum, are spontaneously flammable and highly toxic. Organometallic compounds may form covalent bonds, in which electrons are shared equally between two atoms; multicentre covalent bonds, in which an electron pair is shared between more than two atoms; and ionic bonds, in which the electron pair is donated by only one atom. Polar organometallic compounds (one end of the compound is more negative than the other end) are formed as a result of covalent bonding in which there exists an unequal sharing of electrons between a metal and carbon atom. Polar organometallic compounds are valuable in the synthesis of certain materials and chemicals. For example, alkylaluminum is reacted with titanium salts to catalyze the polymerization of unsaturated hydrocarbons. This reaction is commonly used to catalyze the polymerization of ethylene to polyethylene, a type of plastic. Organometallic compounds containing tin are used as pharmaceuticals, pesticides, and fire retardants. Examples of well-characterized organometallic compounds include tetracarbonylnickel, Ni(CO)4, a volatile nickel compound used in the purification of nickel, and ferrocene, Fe(C5H5)2, a remarkably stable compound in which an iron atom is “sandwiched” between two hydrocarbon rings.
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Any of a class of chemical compounds in which the nitro group (singlehorzbondNO2) forms part of the molecular structure. The most common examples are organic compounds, isomers of nitrite esters in which a carbon atom is linked by a covalent bond to the nitro group's nitrogen atom. Many nitro compounds are commercially used as explosives, solvents, or raw materials and chemical intermediates. They are generally made by a reaction between nitric acid and an organic compound.
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Any substance in which two or more chemical elements other than carbon are combined, nearly always in definite proportions (see bonding), as well as some compounds containing carbon but lacking carbon-carbon bonds (e.g., carbonates, cyanides). Inorganic compounds may be classified by the elements or groups they contain (e.g., oxides, sulfates). The major classes of inorganic polymers are silicones, silanes, silicates, and borates. Coordination compounds (or complexes), an important subclass of inorganic compounds, consist of molecules with a central metal atom (usually a transition element) bonded to one or more nonmetallic ligands (inorganic, organic, or both) and are often intensely coloured. Seealso organic compound.
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Any of a class of organic compounds whose molecules contain one or more rings of atoms with at least one atom (the heteroatom) being an element other than carbon, most frequently oxygen, nitrogen, or sulfur. As in regular cyclic hydrocarbons, such heterocyclic rings may include single, double, or triple bonds or be aromatic (see covalent bond; aromatic compound), and the compound may contain one or more single rings or have fused rings (in which adjoining rings share two carbon atoms). Compounds having five-membered heterocyclic rings include chlorophyll, hemoglobin, indigo, tryptophan, and certain polymers. Those with six-membered heterocyclic rings include pyridine, pyridoxine (vitamin B6; see vitamin B complex), vitamin E, quinine, and the pyran nucleus, which is found in sugars and the anthocyanin pigments. Nicotine and morphine have both five- and six-membered heterocyclic rings; some antibiotics (e.g., penicillin) have two different heteroatoms in their rings. Other important heterocyclic compounds are pyrimidines, which occur in barbiturates, and purines, which occur in caffeine and related compounds; pyrimidine and purine are the parent compounds of the nucleic acids.
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Class of substances with chemical structures made up of a central metal atom surrounded by nonmetal atoms or groups of atoms, known as ligands. Examples of coordination compounds include hemoglobin,
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Machine that uses steam power to perform mechanical work through the agency of heat (hence a prime mover). In a steam engine, hot steam, usually supplied by a boiler, expands under pressure, and part of the heat energy is converted into work. The rest of the heat may be allowed to escape, or, for maximum engine efficiency, the steam may be condensed in a separate apparatus, a condenser, at comparatively low temperature and pressure. For high efficiency, the steam must decrease substantially in temperature as it expands within the engine. The most efficient performance (i.e., the greatest output of work in relation to the heat supplied) is obtained by using a low condenser temperature and a high boiler pressure. Seealso Thomas Newcomen, James Watt.
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Any of a large class of organic compounds whose molecular structure includes one or more planar rings of atoms, usually but not always six carbon atoms. The ring's carbon-carbon bonds (see bonding) are neither single nor double but a type characteristic of these compounds, in which electrons are shared equally with all the atoms around the ring in an electron cloud. The term was first applied circa 1860 to a class of hydrocarbons isolated from coal tar and distinguished by odours much stronger than those of other classes of hydrocarbons. In modern chemistry, aromaticity denotes the chemical behaviour, especially the low reactivity, of this class of molecules related to their bonding. The parent compound of this class is benzene (C6H6). Seealso hydrogenation.
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Any of a class of synthetic plastics, resins, and oils used to manufacture many products. By varying the starting reagents (such as acrylic acid, C3H4O2, or acrylonitrile, C3H3N) and the process of forming, a material may be produced that is hard and transparent, soft and resilient, or a viscous liquid. Acrylic compounds are used to make molded structural and optical parts, jewelry, adhesives, coating compounds, and textile fibres. Lucite and Plexiglas are trademarks used for glasslike acrylic materials.
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Compound may also refer to: