CATEGORIES:
BiologyChemistryConstructionCultureEcologyEconomyElectronicsFinanceGeographyHistoryInformaticsLawMathematicsMechanicsMedicineOtherPedagogyPhilosophyPhysicsPolicyPsychologySociologySportTourism
Analysis of food and drugsChemical analysis plays a major role in helping to maintain high quality control standards for the substances we eat, drink, and use to maintain our health. Many chemicals are added to foods as preservatives, colorants, flavors, emulsifiers (agents that allow liquids to mix without dissolving them), and humectants (moistening agents). It is essential that regular tests are carried out to ensure that the proper food additives in the correct quantities are used. The most sensitive analytical procedures are employed for this purpose. They are also able to detect the presence of minute amounts of chemical impurities. Food and drug analysis is a specialized field. The chemist often has to deal with complex mixtures of natural products (from fruits, cereals, or animals) as well as with synthetic (artificially produced) compounds. Often, this involves complex procedures before full identification by sophisticated procedures. Without such regular analytic checks, the quality of food might be much poorer and harmful additives more likely to be used. One area of considerable importance in food analysis is measuring the alcohol content in beers, wines, and spirits. Many countries charge a tax or duty on such beverages based upon the alcohol content. Accurate methods of measurement are important for levying the correct amount of duty. Clinical analysis Diseases and other medical disorders lead to changes in the concentration and production of various chemicals in the human body. In the diagnosis of medical conditions, clinical analysis plays an important part. For example, simple chemical tests for glucose (sugar) in the blood or urine can reveal whether or not a person is diabetic. A type of spectrometry is used extensively for measuring sodium, potassium, and calcium concentrations. Other analytic methods are employed for measuring different substances in the body. An imbalance of any substance can indicate bodily disorders. The demand for chemical analyses for medical purposes is now so great that automatic methods of analysis are used whenever possible. Forensic analysis An area of growing importance in chemical analysis is in the detection of crime and the conviction of criminals. This is known as forensic analysis. For this purpose, almost every analytical tool is called into play. For instance, it is possible to determine whether or not a fire has been started deliberately. Ashes and debris can be analyzed for the presence of kerosene, gasoline, or solvents. Gas chromatography is used for this purpose. It can detect not only the main materials used to start the fire, but also the identity of its individual components. Similarly, the conviction of illegal drug sellers depends upon correct identification of what are often apparently only white powders. It is necessary to differentiate correctly between innocent sugar, talcum powder, and flour, and the illegal drugs morphine, heroin, and cocaine. Chromatographic methods are used in conjunction with infrared and mass spectrometry. There is no end to the variety of analyses forensic scientists have to carry out. These include the identification of glass fragments, the chemical nature of paint flakes, and the composition of inks. One of the major tasks in many countries is the regular analysis of blood samples. This is done to determine the blood alcohol levels in motorists found driving under the influence of alcohol. In cases such as this, the analyst may have to to stand up in court to explain his/her results. Quality control One of the major uses of chemical analysis is in maintaining quality control in the chemical industry itself. The demand for purer chemicals and materials has led, in turn, to great improvements in analytical methods. As chemicals are manufactured, their rate of production is often checked automatically by on-line analytical equipment. The final material also undergoes rigorous tests. This ensures that it is the correct material and that it satisfies the specification for the quality required. Even minute amounts of impurities can cause it to be rejected as unsuitable. Such quality control is of immense importance with chemicals that are used for human consumption or use, such as pharmaceuticals (drugs) and cosmetics. Even household products such as polishes, bleaches, detergents, Analytical chemistry: Uses of analysis 143
and paints all require proper analytical checks to ensure that the correct amounts of chemicals have been mixed and that they are safe to use. In a similar way, the metals used to make such products as cars and aircraft must meet strict quality specifications. The presence of any impurities can cause corrosion to occur very rapidly. In this area, spectroscopic and surface analysis methods are of prime importance. Building materials (bricks, cement, and plaster) and adhesives are all substances that deteriorate rapidly if they are incorrectly made. Careful quality control is necessary to maintain high standards. Chemical analysis is, therefore, an essential step in maintaining the quality of most of the products we use. Accurate weighingremains the basis of most quantitative techniques, if only in the preparation of samples for subsequent automatic analysis. Delicate mechanical precision is combined with modern electronics in the mechanism of a modern balance (top left). The simpler machine (above) displays a direct digital reading. In forensic analysis,microscopic (visual) examination often precedes chemical treatment of samples from the scene of a crime.
A revolution in chemical analysishas been brought about by the use of sophisticated instruments and computers. Despite these improvements, there will probably always remain a need for individual laboratory techniques in connection with most industries. There are hardly any industrial processes that do not require the services of chemistry at some stage or other. GLOSSARY
A absorptionA process in which a substance takes up another substance, such as blotting paper (a solid) absorbing water (a liquid). Or a process in which a substance takes up radiation of a characteristic wavelength. The latter process is of importance in spectroscopic analysis. See also adsorption; spectroscopy. acidA substance from which a hydrogen ion can be released in aqueous (made of water) solution. The strength of an acid depends on the ease with which the hydrogen ion dissociates from the rest of the molecule. The strength is measured by its ph, which is always less than 7. See also base; carboxylic acid; hydro GEN ION CONCENTRATION. actinideOne of a group of elements that starts with actinium (element 89) and concludes with lawrencium (element 103). Like the lanthanides, the actinides form a separate group within the periodic table. In these groups, an inner shell of electrons fills up as the atomic number increases. See also electron; element; lanthanide. activation energyThe energy needed in order to form a transition state, the unstable middle stage that occurs during a chemical reaction. This middle stage is at a higher energy level than either the reactant(s) or the product(s). Its formation consequently requires the surmounting of an energy barrier. addition reactionA chemical reaction in which the product is formed by combining two separate molecules. It most frequently refers to the breaking of a multiple bond between two carbon atoms and the subsequent formation of two new single bonds to other atoms. See also atom; molecule. adenosine triphosphateAn organic compound used by living organisms as a means of transferring energy between other compounds. Also known as atp, it is the readily accessible energy used by all plants, animals, and bacteria. adsorptionA process in which a substance adheres to the surface of another substance. Adsorption is important in some types of catalysis, notably where gases adsorb on metal surfaces. The reaction is then made easier by a consequent lowering of activation energy. See also absorption. alcoholAn organic chemical substance that contains a hydroxyl group. It is often taken to refer specifically to ethanol (ethyl alcohol), the intoxicating part of alcoholic beverages. See also organic chemistry. aldehydeAn organic chemical substance that contains acarbonyl group. See also ketone; organic chemistry. alicyclicSee cyclic. aliphaticA type of organic chemical substance consisting primarily of a chain of carbon atoms. See also or GANIC CHEMISTRY. alkaliOne of the six metallic elements that make up Group 1A of the periodic table. These are lithium, sodium, potassium, rubidium, cesium, and francium. Alkali can also refer to a base formed from the union of a hydroxide (a molecule of oxygen and hydrogen) and an alkali metal. alkaloidAny one of a large family of organic compounds found in plants and having a basic nitrogen atom incorporated into a heterocyclic structure. Most of them are physiologically active. See also compound; HETEROCYCLE; ORGANIC CHEMISTRY. alkaneA saturated aliphatic hydrocarbon in which all the carbon and hydrogen atoms are joined to each other by single bonds. Formerly known also as a paraffin. See also atom; bond. alkeneAn aliphatic hydrocarbon that contains at least one carbon-carbon double bond, for example, ethene or ethylene. Formerly known also as an olefin. alkyl groupAn aliphatic hydrocarbon group from which a hydrogen atom has been removed. Because of the missing hydrogen atom, the group is able to form a single bond between one of its carbon atoms and another atom, or group of atoms, to form a more complex compound. An alkyl group often combines with a halogen in order to form a halogenated hydrocarbon. alkyneAn aliphatic hydrocarbon that contains at least one carbon-carbon triple bond. allotropyThe occurrence of a chemical element in two or more physical forms. Each form has the same kind of atom, but the number and arrangement of the atoms are different This makes each form physically and chemically different. alloyA mixture of two or more metals, combined in order to produce a material with more useful properties than any of the components individually. For example, niobium, a hard metal, cannot be formed easily into complex shapes. Iron is malleable. Thus, niobium alloyed with iron produces a hard, but malleable, steel. See also metal. alpha particleA particle made up of two protons and two neutrons. This particle is emitted during the breakdown of some radioactive elements. If the particle acquires two electrons, it becomes an atom of helium. See also ionizing radiation; neutron; proton; radioactivity. amineA compound in which one (or more) of the hydro-
CHEMISTRY. amino acidAny one of a group of complex organic compounds of nitrogen, hydrogen, carbon, and oxygen that combine in various ways to form the proteins that make up living matter. See also compound; PROTEIN. analytical chemistryThe determination of the properties of chemical substances and the structure and composition of compounds and mixtures. See also COMPOUND. anionAn ion that has a greater number of electrons associated with it than there are protons in its atomic nucleus (or nuclei). Consequently, an anion carries a negative electric charge. See also cation; electron; pro TON. anodeA positive electrode—that is, one toward which anions move during electrolysis. See also anion; cathode. antibioticA substance produced by a living organism, especially a bacterium or a fungus. An antibiotic destroys or weakens germs. antibodyA protein substance produced in the blood or tissues of animals or humans. An antibody destroys or weakens bacteria or neutralizes the poisons they produce. See also vaccine. argononSee rare gas. aromaticityThe phenomenon in which some of the electrons linking carbon atoms together into ring structures are shared by all the atoms in the ring. The electrons are known as delocalized electrons. See also ATOM; DELOCALIZED ELECTRON; ELECTRON. asymmetryA carbon atom in an organic compound is linked by single chemical bonds to each of four different atoms or groups of atoms. The structure of the carbon molecule is thus asymmetrical. One half of it is not a mirror image of the other half. See also BOND; COMPOUND; MOLECULE. atomThe smallest amount of any element that can exist, while still having the properties characteristic of that element. See also electron; neutron; proton. atomic numberThe number of protons in the nucleus of an atom of a chemical element. Because each element has a different number of protons, there is a different atomic number for each element. See also proton. ATPSee adenosine triphosphate. B baseA substance that reacts with an acid to form a salt. An aqueous (made of water) solution of a base always has a ph of greater than 7. See also alkali. beta particleAn energetic electron emitted from a nucleus when a neutron changes into a proton during radioactive breakdown of an atom. See also radioactivity. biochemistryThe branch of chemistry that is concerned with the chemical substances and reactions that occur in living organisms. See also reaction. bondA unit of force by means of which atoms or groups of atoms are combined or joined together in a molecule. A chemical bond usually consists of a pair of shared electrons. Two pairs of shared electrons form a double bond. Three pairs of shared electrons form a triple bond. See also atom; coordinate BOND; COVALENT BOND; ELECTRON; IONIC BOND; MOLECULE. c carbohydrateAn organic chemical compound made up solely of carbon, hydrogen, and oxygen atoms. Usually, the ratio of hydrogen to oxygen atoms is 2:1, as in water (H20). Carbohydrates include many compounds important in living processes, such as cellulose, starch, and sugar. carbonyl groupAn organic chemical group in which an oxygen atom is doubly-bonded to a carbon atom. The carbon atom is, in turn, bonded to other carbon or hydrogen atoms. Ketones and aldehydes are the main classes of compound containing a carbonyl group. See also aldehyde; ketone. carboxyl groupAn organic chemical compound made up of a carbonyl group and a hydroxyl croup. Carboxyl groups are the chief ingredients of organic acids. See also acid; organic chemistry. carboxylic acidAny organic acid that contains the carboxyl group. See also acid; organic chemistry. catalysisThe process by which a nonreacting substance (the catalyst) lowers the activation energy of a re-acton involving one or more other substances. This means that the reaction proceeds faster and under milder conditions than would be possible without the catalyst. See also catalyst. catalystA substance that causes and/or speeds up a chemical reaction while itself remaining practically unchanged. See also catalysis. cathodeA negative electrode, that is, one toward which cations move during electrolysis. See also anode; cation. cationAn ion that has a smaller number of electrons associated with it than there are protons in its atomic nucleus (or nuclei). Consequently, a cation carries a positive electric charge. See also anion; electron; proton. celluloseA carbohydrate polymer that occurs widely in plants as a structural material. Cotton and paper are both made from cellulose fibers. chain reactionA chemical reaction in which the energy or substances produced encourage more of the starting materials to react, so that the reaction becomes self-sustaining. If the effect of the initial reaction is very great, the reaction may become explosively fast. Chain reactions also occur at the subatomic level, as during the explosion of an atomic bomb. chelationThe property of some molecules to physically hold onto a metal ion. Chelating agents are useful in removing unwanted metal ions from solutions, and for identifying particular ions in analytical chemistry. See also solution. chlorophyllAn organic compound containing magnesium. Chlorophyll is the green coloring matter of plants, without which photosynthesis would be impossible. chromatographyA technique for separating similar chemical compounds from one another by using differences in the strength of their adsorption on an inert material. It is widely used in analytical chemistry and also in separating and purifying some high-value compounds. See also compound. chromophoreA part of a molecule that produces the color within the molecules of colored organic compounds. codonA group of three organic bases in a stretch of dna. These bases code for a specific amino acid during protein synthesis. coenzymeA small nonprotein molecule that combines with the protein of an enzyme. Coenzymes are essential to the functioning of many enzymes. However, not all enzymes require coenzymes. Some types of vitamin are needed in the diet because they act as coenzymes. complexA compound in which a central atom is surrounded by other atoms, ions, or small molecules, known as ligands. See also coordination number; ion; molecule. compoundA substance made up of heterogeneous molecules. A compound must contain at least two different elements. See also element; molecule. concentrationThe amount of a particular substance present in a defined volume. The term is used most frequently to refer to the amount of a solid or liquid Glossary 147
also MOLECULE. conductivityA measure of the ability of a material to pass electricity, heat, sound, or other forms of energy. See also metal; superconductivity. coordinate bondA type of covalent bond in which one atom supplies both electrons that bind two atoms together, rather than each atom supplying one electron. See also bond. coordination compoundSee complex. coordination numberThe number of ligands that surround the central ion or atom of a complex. See also licand. corrosionThe breakdown of materials made of metal under natural conditions, such as the rusting of iron. covalent bondA chemical bond between two atoms in which a pair(s) of electrons (one from each atom) is shared by both atoms. An equal number of electrons originates from each atom. See also coordinate bond; electron. crackingThe breaking down of big molecules into smaller ones. The process usually refers to the breaking down and reforming of hydrocarbons from crude oil. Cracking is used in producing ordinary gasoline. See also hydrocarbon; molecule. cyclicA type of organic chemical substance in which a chain of carbon atoms is linked together end to end to form a ring structure. See also aliphatic; atom; organic CHEMISTRY. D daltonA unit of atomic and molecular mass. It is defined as one-twelfth of the mass of a neutral atom of the carbon isotope. This atom contains six protons and six neutrons in its nucleus. It is named after the eighteenth-century English chemist John Dalton. See also MOLECULE; NEUTRON; PROTON. delocalized electronOne of several electrons that are spread evenly around an aromatic hydrocarbon ring, forming two doughnut-shaped clouds. Also known as pi-electron. See also aromaticity; electron. deoxyribonucleic acid Anucleic acid found in the nucleus of most living cells. It is the substance of which most genes are made. It is chiefly responsible for the transmission of inherited characteristics and the development of an organism according to those characteristics. Commonly known as DNA. See also gene; RIBONUCLEIC ACID. DNASee deoxyribonucleic acid. E electrodeA material used to pass an electric current through a liquid or gas. A positive electrode is called an anode, a negative electrode a cathode. See also electrolysis. electrolysisThe breakdown of a compound, usually in solution or as a liquid, when an electric current is passed through it. Under the influence of the current, the compound is reduced to ions. The negative ions (anions) migrate to the positive electrode (anode). There, the electrical charge is neutralized. The anions are either liberated or react with the surrounding medium. The positive ions (cations) migrate to the negative electrode (cathode), where a similar change takes place. See also anion; cation; ion. electromagnetic spectrumThe entire range of the different types of electromagnetic radiation. This radiation is made up of an electric and a magnetic field that travel in waves. The spectrum covers (from short to long wavelengths) cosmic rays, camma ray(s), x ray(s), ultraviolet radiation, visible light, infrared radiation, micro-wave(s), and radio waves. Because the energy associated with radiation decreases with increasing wavelength, the different types of radiation interact differently with substances. See also ionizing radiation; WAVELENGTH. electronA small subatomic particle that orbits the nucleus in an atom. It has a negative electric charge and a mass nearly 2,000 times less than that of the proton and neutron. Nevertheless, it is the part of the atom that contributes most to its chemical properties. electroplatingA process in which a thin layer of metal is deposited on the surface of another metal by elec trolysis. The metal that is to be deposited is held in solution as cations. The metal to be coated acts as a cathode. elementA substance composed of atoms whose nuclei all contain the same number of protons. Elements are the basic atomic building blocks of matter. There are 109 known elements. See also atom; nucleus; proton. endothermic reactionA chemical reaction that has to absorb energy (not necessarily as heat) in order to take place. See also exothermic reaction. enzymeA large organic molecule, consisting mostly or entirely of protein. An enzyme acts as a catalyst in a living system. See also organic chemistry. equilibrium Inany reaction, there is always a fixed proportion of reactants and products. This holds true provided that materials and energy are not added or taken away and that the system is kept undisturbed for a long enough time. In such a situation, the reaction is at a state of chemical equilibrium. Much of practical chemistry is aimed at disturbing the equilibrium of reactions. This produces extra quantities of desired products. Catalysts are also often used to decrease the time necessary to reach equilibrium. See also catalyst; reactant. esterificationA reaction involving an acid (usually carbox-ylicacid) and an alcohol, which produces an ester. Esterification is a type of condensation reaction. exothermic reactionA chemical reaction that liberates energy, usually but not necessarily as heat. See also endothermic reaction. F fermentationThe microbiological process in which a sugar is converted to ethanol (alcohol) by yeast cells. Carbon dioxide is also produced as a by-product. Yeast fermentation or fermentation by bacteria is also used in the making of various other products, including bread, cheese, and yogurt. The term also refers to the industrial production of any useful material (for example, an antibiotic) by a microorganism. A microorganism is an animal or vegetable organism that can only be seen with a microscope. fluorescenceA phenomenon exhibited by various substances that are able to absorb light of a particular wavelength, but emit light of another wavelength. See also phosphorescence. free radical Anatom or group of atoms in which there is an unpaired electron. This makes the radical highly reactive. Free radicals are formed when a chemical bond breaks in such a way that one free electron remains with each molecular fragment. They are often important intermediates in a reaction, particularly a CHAIN REACTION. G gamma rayPenetrating electromagnetic radiation of short wavelencth (very high frequency). Gamma rays are emitted during the radioactive decay of certain elements such as radium. See also electromagnetic spectrum; radioactivity.
H half-lifeThe time taken for half of any amount of a radioactive isotope to decay. The half-life for different isotopes varies between small fractions of a second and many thousands of years. See also radioactivity. halideA chemical substance that contains one or more atoms of the halogen elements. See also atom; element. halogenAny one of the chemical elements of Group 7A of the periodic table: fluorine, chlorine, bromine, iodine, and astatine. See also element; periodic table. heterocyclic compoundAn organic chemical compound containing one or more rings of atoms, with at least one atom other than carbon in one of the rings. See also organic chemistry. heterogeneousReferring to molecules composed of atoms of different elements. See also atom; element; homogeneous; molecule. hexoseA simple sugar consisting of six carbon atoms, for example, glucose. See also atom; pentose; triose. homogeneousHaving a uniform makeup. Homogeneous may refer to a molecule in which all the atoms are the same. Or it may refer to a mixture, such as a solution, in which the parts are thoroughly and evenly mixed. See also atom. hormoneA substance formed in the endocrine glands of animals and humans. It enters the bloodstream and affects or controls the activity of cells, tissues, or organs. A number of similarly active materials produced by plants are also loosely referred to as hormones. See also pheromone. hydrocarbonAn organic chemical substance consisting solely of carbon and hydrogen atoms. Saturated hydrocarbons have all their carbon atoms joined by single bonds. Their remaining bonding capacity is taken up by hydrogen atoms. Unsaturated hydrocarbons have one or more carbon-carbon multiple bonds. Hydrocarbons may be aliphatic, cyclic, or aromatic. They are obtained primarily from crude oil and are among the most important raw materials of the chemical industry. See also aromaticity; atom; bond; organic chemistry. hydrogen bondA weak bond in a molecule between a hydrogen atom and an unshared pair of electrons in another atom, such as oxygen. The hydrogen bond is only a fraction as strong as an ordinary covalent bond. However, it plays an essential role in determining the shape of many complex molecules of biological importance, such as DNA. See also electron; deoxyribonucleic acid. hydrogen ion concentrationThe concentration of hydrogen ions in a solution, which dictates whether the solution is acidic, basic, or neutral. Many compounds dissociate (separate) either completely or partly in solution into electrically charged ions. Even pure water, which consists of molecules of hydrogen oxide (H20), contains some dissociated hydrogen (H+) and hydroxyl (OH) ions. As the amounts of each type of ion are equal, pure water is a neutral liquid. An excess of hydrogen ions makes a solution acidic. A basic solution has an excess of hydroxyl ions. The hydrogen ion concentration of a solution is expressed as a mathematical function called the ph. A pH of less than 7 indicates an acidic solution, one of greater than 7, a basic solution. See also acid; base; COMPOUND; MOLECULE. hydrophilicHaving an attraction for water. Hydrophilic substances dissolve readily in water. See also hydrophobic surfactant. hydrophobicHaving an aversion to water. Hydrophobic substances, such as oil, do not dissolve in water. See also HYDROPHILIC; SURFACTANT. hydroxyl groupA radical consisting of a hydrogen atom bonded to an oxygen atom. I inert gasSee rare gas, infrared radiationRadiation that is in the invisible part of the electromagnetic spectrum, between the red end of visible light and microwaves. Infrared spectroscopy is a useful analytical tool. Most of the heat from sunlight and lamps is from infrared rays. inhibitionPrevention of a reaction from taking place, either wholly or in part. Inhibition is of particular importance in reactions involving an enzyme. A substance (the inhibitor) can interact with an enzyme and prevent another substance, with which the enzyme is meant to react, from coming into contact with it. inorganic chemistryChemistry of elements other than carbon. Inorganic chemistry includes compounds that contain carbon atoms, provided these are not joined to each other. See also atom; compound; element; organic chemistry. intermediate stateSee transition state. ionAn atom or group of atoms that contains either more or less electrons associated with it than there are protons. Consequently, all ions carry either negative or positive charges. The two types are known, respectively, as anions and cations. An ion may have more than one unit of charge. See also electron; proton. ionic bondA chemical bond between two atoms formed when one atom loses one or more electrons to the other atom. An ionic bond is thus a bond between two ions with opposite charges. See also electron; ion. ionizing radiationRadiation that interacts with matter to form ions. The short wavelengths of the electromagnetic spectrum, which include gamma and X rays, are a form of ionizing radiation. So are some particles, such as alpha particles. Ionizing radiation is most closely associated with radioactivity. See also alpha particle; ION; WAVELENGTH. isomerismThe phenomenon whereby the same number and types of atoms may join together in different ways. Thus, more than one distinct chemical compound (called an isomer) can be formed from the same parts. Isomers have the same chemical composition, but different structural arrangements. See also OPTICAL ISOMERISM; STEREOISOMERISM. isotopeAn atom of an element with a specific number of neutrons. The number of protons in an atom cannot vary without the atom changing its elemental identity. However, the number of neutrons can vary, although only over a small range. Most elements in their natural form are made from mixtures of two or three different isotopes. Generally, an element has very few stable isotopes. Unstable isotopes can break down with the emission of ionizing radiation. See alSO NEUTRON; PROTON; RADIOACTIVITY. K ketoneAn organic chemical substance in which one carbon atom is attached to an oxygen atom by a double bond and to two other carbon atoms by single bonds. See also aldehyde; organic chemistry. L lanthanideOne of a group of elements that starts with lanthanum (element 57) and concludes with lutetium (element 71). They are silver-colored metals in their pure form. Like the actinides, the Ianthanides form a separate group within the periodic table. See also acti- NIDE; ELEMENT; METAL Glossary 149
PAIR; TRANSITION ELEMENT. lipidAny one of a group of organic compounds that contain long chains or ring systems of carbon atoms. Lipids, which include fats, oils, and waxes, are insoluble in water. See also atom; compound. lone pairA pair of electrons in the outer shell of an atom. When the pair forms a coordinate bond in a complex, the atom containing the electrons is known as a ligand. See also electron. M macromoleculeA large and complex molecule made up of many smaller molecules linked together. A polymer is a macromolecule. mass numberThe atomic weight of an atom, equal to the sum of the protons and neutrons in the nucleus. See also neutron; proton. metalAn element or mixture of elements that conducts heat and electricity well and is lustrous, malleable, and ductile. In metals, the atoms are all closely bound together. The electrons, however, are mobile. This accounts for the electrical conductivity. Of 109 known elements, 86 are metals. Some elements that lie adjacent to metals in the periodic table show partly metallic and partly nonmetallic characteristics. These elements are called metalloids. See also atom; electron. microwaveRadiation that lies between infrared radiation and short radio waves in the electromagnetic spectrum. molecular biologyThe branch of biology dealing with the chemical processes of life at the molecular level. Much of molecular biology can be classed as biochemistry. See also molecule. moleculeAny group of atoms linked together by one or more chemical bonds. A homogeneous molecule is one in which the atoms involved are all of the same element. Molecules composed of more than one type of atom are called heterogeneous. All chemical compounds are composed of heterogeneous molecules. See also bond; compound. monomerA small molecule that forms a polymer when joined together in large numbers. monosaccharideA simple sugar made of three to seven atoms of carbon in the shape of a chain. Monosaccharides include fructose and glucose. See also atom; polysaccharide. N neutralizationThe treatment of an acid with a base (or vice versa) to form a salt. At the end of the reaction, neither of the original components remains in excess. neutronOne of the three subatomic particles from which atoms are made. Like the proton, the neutron forms part of the nucleus of an atom. Unlike the proton and the electron, it carries no electrical charge. noble gasSee rare gas. nuclear fissionThe splitting that occurs when the nucleus of an atom absorbs a neutron. The atom then divides into two nearly equal parts and releases large amounts of energy. Nuclear fission can be produced by neutron bombardment of the atom, as in the atomic bomb. See also nuclear fusion. nuclear fusionThe combining of two atomic nuclei to create a nucleus of greater mass. The fusion of the atomic nuclei of elements of low atomic number requires a very high temperature and releases tremendous amounts of energy. Fusion is used to produce the reaction in the hydrogen bomb. See also atom; ELEMENT; NUCLEAR FISSION. nucleic acidA macromolecule consisting of linked nucleotides. Nucleic acid is found in all living cells, chiefly in combination with proteins. There are two kinds of nucleic acids: DNA and RNA. See also deoxyribonucleic ACID; NUCLEOTIDE; PROTEIN; RIBONUCLEIC ACID. nucleotideAn organic chemical compound consisting of three different molecules: an organic base, a sucar, and phosphoric acid, nucleic acid and some important biological molecules, such as ATP, are made of nucleotides. See also adenosine triphosphate; molecule; organic chemistry. nucleusThe central part of an atom, consisting of proton(s) and neutron(s). The only exception is hydrogen, whose nucleus consists solely of one proton. In biochemistry, nucleus may be used to refer to the part of a living cell in which most of the nucleic acid is found. o olefinThe former name for an alkene. orbitalThe volume of space in which there is a high probability of finding a particular electron. Because the electron has characteristics of both a wave and a particle, its position at any time cannot be determined accurately. It is possible to express its position only in terms of probability. Each electron in an atom occupies an atomic orbital. When two electrons link two different nuclei in a molecule, they share a volume of space that is called a molecular orbital. See also nucleus. organic chemistryThe chemistry of molecules consisting primarily of carbon atoms linked together in chains or rings. At one time, it was believed that such substances could be obtained only from matter that was or had been alive, hence the name organic. See also atom; inorganic chemistry; molecule. oxidationA reaction in which the formal electric charge on an atom becomes more positive. Although this includes all reactions in which oxygen is added to an element or compound, it is not restricted to reactions involving oxygen. See also reduction. P paraffinThe former name for an alkane. pentoseA simple sugar consisting of five carbon atoms. Ribose, a sugar found in ribonucleic acid, is a pentose. See also atom; hexose; triose. peptideA relatively small molecule comprised of a few amino acids linked together in the same way as in a protein. The dividing line between peptides and proteins is not sharply defined. See also amino acid. periodic tableA table in which the chemical elements are arranged in the order of their atomic numbers. The periodic table also groups together elements with similar properties. See also atomic number; element. pH The measure of the acid or base character of a liquid or solution. The measure is based upon the hydrogen ion concentration of the liquid or solution. The measure is expressed as a number from 0 to 14. The hydrogen ion concentration of pure water is neutral and is given the measure of pH7. Liquids going from pH6 to pHO are increasingly acidic. Liquids going from pH8 to pH14 are increasingly alkaline (basic). pheromoneA substance secreted externally by certain animal species, especially insects, to affect the behavior or development of other members of the species. Pheromones show a HORMONE-like behavior. phosphorescenceA phenomenon exhibited by various substances that absorb light of a particular wavelength, but emit light of a different wavelength. Unlike fluo rescence, which occurs only while a light source is present, phosphorescence persists after that source has been removed. photochemistryThe study of chemical reactions that
Glossary
photosynthesisThe process by which plant cells make carbohydrates from carbon dioxide and water in the presence of chlorophyll and light. Oxygen is released as a by-product. See also carbohydrate. plasticA synthetic organic polymer made from coal, water, limestone, or other similar basic raw materials. Plastics can be shaped either during their formation or afterwards by application of heat. Plastics that soften and harden reversibly on heating and cooling are called thermoplastics. The term plastic originally referred to the behavior of any type of material that would deform easily. Sometimes, it is still used in this way. polymerA macromolecule made by linking together many monomers. Usually, a polymer contains no more than three different types of monomer. Polymers derived from a single type of monomer are called homopolymers. Nylon and cellulose are polymers. polysaccharideA polymer formed by linking together simple sugars. Polysaccharides may contain many thousands of monosaccharide units. They occur widely in living organisms, where they are used primarily to store energy. See also sugar. precipitateA solid substance that comes out of a solu-tion. This results either from concentrating the solution or from a chemical reaction that leads to an insoluble product or products. proteinA polymer formed by linking together amino acids. Proteins play vital roles in living organisms. See also amino acid; peptide. protonOne of three subatomic particles from which an atom is made. Together with neutron(s), proton(s) form the nucleus of an atom. Each proton has a single unit of positive electrical charge. In a neutral atom, this charge is balanced by the negative charge of an electron. Q quantum numberOne of four numbers that define the state of an electron in an atom. The numbers indicate the energy level of the electron, the shape of its orbital, and its spin. No two electrons in an atom can have all four quantum numbers the same. R radiationSee electromagnetic spectrum; ionizing radiation. radical Anatom or group of atoms acting as a unit in a chemical reaction. A radical behaves as if it were a single element instead of two or more. A radical is sometimes called a functional group. radioactivity The decay of an unstable elemental nucleus. This is accompanied by the emission of small particles, such as alpha particles (helium nuclei) or beta particles (electrons), and gamma rays. See also alpha PARTICLE; BETA PARTICLE; ELEMENT; GAMMA RAY. rare earthSee lanthanide. rare gasOne of the elements comprising Croup 8A of the periodic table. These are helium, neon, argon, krypton, xenon, and radon. They are also known as the inert or noble gases, or the argonons. See also element. reactantAn element or compound that enters into a chemical REACTION. reactionThe chemical process by which one or more substances change into one or more different substances. A reaction involves a reactant(s), a reagent, often a catalyst, a transition state, and the product(s). reagentA chemical substance that is used as a starting material in a chemical reaction. A reagent can also be used to detect the presence of other substances by the chemical reactions it causes. reductionA type of reaction in which the formal electric charge on an atom becomes more negative. See also OXIDATION. ribonucleic acidA nucleic acid found in the cells of all living organisms. Commonly known as RNA, it transfers the genetic code embedded in DNA to the ribo-somes, and is involved in the synthesis of protein. In some types of virus, the RNA is the genetic material rather than DNA. See also deoxyribonucleic acid; cene; ribo some. ribosomeA small particle that consists largely of ribonu cleicacid. It is found in all living cells, where it carries OUt the SYNTHESIS Of PROTEIN. RNASee ribonucleic acid. s saltA chemical substance that exists as an ionic solid. Salts are formed when an acid and a base neutralize each other. Most salts are composed of metal cation(s) and anion(s) of certain element(s). Common, or table salt is a compound of sodium and chlorine. See also ION; NEUTRALIZATION. saponificationThe breakdown of an ester into an alcohol and a salt of carboxylic acid. This reaction happens in the presence of a base. The name derives from the original method for producing soap. saturationThe involvement of all bonding electrons of an atom, usually carbon, in single bonds with other atoms. Saturation can also refer to the state of a solution that can dissolve no more solute. See also bond; electron. shellA layer of electrons surrounding the nucleus of an atom, all at approximately the same distance from the nucleus. Electrons in different shells are at different average distances from the nucleus. It is usually only those electrons in the outermost shell that participate in chemical reactions. The first quantum number indicates the shell in which an electron occurs. See also reaction. soluteA substance, usually solid, that is dissolved in a liquid (the solvent) to form a solution. solutionA homogeneous mixture of two or more different substances, usually a solid (the solute) in a liquid (the solvent). solventA liquid in which a substance (the solute) is dissolved to form a solution. spectroscopyThe study of the absorption or emission of electromagnetic radiation by substances. It provides chemists with a range of techniques for identifying a compound according to the characteristics of its spectrum (wavelength range). Spectroscopy is divided into several different types, such as infrared and ultraviolet, according to the wavelengths of the electromagnetic spectrum that are used. spectrumSee electromagnetic spectrum. starchA carbohydrate polymer found widely in plants, which use it as a means of storing energy. stereoisomerismA form of isomerism in which the same number and types of Iigands can join together in different ways to form two or more distinct complexes. Such complexes are known as stereoisomers. When the stereoisomers are mirror images of each other, they are known as optical isomers. See also complex; ligand. steroidOne of a class of biologically active compounds characterized by a skeleton made up of four fused carbon rings. Steroids are important as vitamins and hormones. See also compound; hormone; vitamin. sublimationThe process in which a solid turns to a vapor without passing through an intermediate liquid state. Whether this can happen or not depends on the substance involved and the temperature and pressure to which it is subjected. Few substances sublime at ordinary atmospheric pressure and mod- Glossary 151 erate temperatures. sugar Asmall carbohydrate molecule. The term sugar often refers to the compound sucrose. See also hexose; pentose; TRIOSE. superconductivityA phenomenon observed primarily at extremely low temperatures in which the electrical conductivity of a substance increases dramatically. synthesisThe process by which complex molecules are made from simpler molecules. See also molecule. tautomerismThe interconversion of two isomeric forms (or tautomers) of a molecule. Some substances can exist as combinations of different tautomers. These forms interchange readily so that an equilibrium can be maintained. See also isomer. titrationA determination of the strength or nature of a solution. A solution containing a specific concentration of a known substance is added to the unknown solution. The known substance in the first solution will react in some way with the solute in the unknown solution. The most common use of titration is to determine the strength of an acid solution by titration with a base, or vice versa. In such cases, a special kind of indicator shows when all the unknown material has been neutralized. See also neutralization; reaction. transition element Anelement belonging to one of the following groups in the periodic table: 4B, 5B, 6B, 7B, or 8B. These groups occupy the middle of the table and exclude the elements 104 through 109. The transition elements are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum. transition stateThe intermediate state in a chemical reaction between reactant(s) and product(s). The transition state is at a higher energy than either reactants or products. Its formation represents an energy barrier that has to be overcome if a reaction is to occur. See also activation energy. triglycerideA naturally-occurring fat or oil that is formed by esterification of three molecules of carboxyl-icacid and one molecule of the alcohol glycerol. trioseA simple sucar consisting of three carbon atoms. See also atom; hexose; pentose. U ultraviolet radiationElectromagnetic radiation whose wavelength falls on the electromagnetic spectrum between X rays and visible light. The ultraviolet wavelengths are important in spectroscopy. They also strongly influence certain types of chemical reaction. unsaturated compoundAn organic chemical compound that contains at least two carbon atoms joined by a multiple bond. See also atom; organic chemistry; unsatura- TION. unsaturationThe state of an atom in which it is bound to fewer other atoms than is theoretically possible, assuming a single (two-ELEcrRON) bond between each pair of atoms. Most frequently, unsaturation denotes the linking of carbon atoms by double or triple bonds. These can be broken so as to leave a single bond still holding the two atoms together. trons can participate in bond formation with other atoms. The valence of an atom is often equal to the number of electrons it needs to lose or gain (whichever is the less) in order to fill its outermost shell with electrons. However, many elements, particularly a transition element, can have variable valence values. virusA microorganism that causes certain infectious diseases. A virus is capable of taking over part of the mechanism (deoxyribonucleic acidi of a living cell in order to reproduce itself. This is because many viruses consist solely of ribonucleic acid and protein. vitaminAny one of certain special substances necessary for the normal growth and proper nourishment of the body. The body is usually unable to synthesize vitamins by itself. Most vitamins are complex protein compounds that act as coenzymes. See also coenzyme. w wavelengthA property of electromagnetic radiation. Such radiation has wavelike characteristics. Wavelength is the distance between one peak of a wave and the next corresponding peak. Wavelengths in the electromagnetic spectrum vary between about 10 tril-Iionths of a meter for the shortest cosmic rays to 10,000 meters for the longest radio waves. This is equivalent to a range of about 400 trillionths of an inch up to about 6 miles. X rayElectromagnetic radiation that has a wavelength on the electromagnetic spectrum between that of gamma rays and ultraviolet radiation.
valenceThe combining power of an atom. A valence electron is usually in the outermost shell. Such elec- Index
Acetals, 82-83 Acetyl coenzyme A, 118 Acid, 84-85, 145 Actinide, 60-61, 145 Actinium, 58, 60, 61 Adenosine diphosphate (ADP), 117 Adenosine triphosphate (ATP), 116-117, 118, 145 Alcohols, 80-82, 145 multifunctional, 81 structure, 80 Aldehydes, 82-83, 145 Alkali metals, 26-27 Alkaline earth elements, 30-31 Alkaloids, 9, 94, 145 Alkanes, 68, 69, 70, 145 liquefied, 69 production and uses, 68-69 Alkenes, 72-73, 145 Alkynes, 73, 145 Allotrope, 37 Allotropy, 37, 145 Alloys, 28, 62-63, 145 aluminum, 35 amalgam, 33 ferrovanadium, 40 interstitial, 63 invar, 41 nickel-iron, 41 nickel-silver, 41 osmium-iridium, 45 platinum-iridium, 44 platinum-rhodium, 44 substitutional, 63 Alum, 35 Aluminum, 34-35, 58 Aluminum boride, 34 Amides, 88, 89 Amines, 88, 145-146 Amino acids, 110-111, 146 Ammonia, 46-47, 88 Anion, 20, 146 Anthocyanins, 96 Anthracene, 76-77 Antimony, 48, 49 Arfvedson, )ohann, 27 Argon, 56, 57 Arsenic, 48-49 Artificial sweeteners, 95 Asphalt, 77 Astatine, 54, 55 Atomic absorption, 130 Atomic number, 12 Atomic theory of matter, 8-9 Atoms, 12-13, 18, 146 atomic number, 12, 146 electronegative, 15 electropositive, 15 isotopes, 12 mass number, 12, 149 neutral state, 20 neutrons, 12 nucleus, 12, 13 orbitals, 12 Automated analysis, 140-141 Automatic sampler, 141 Azo dyestuffs, 96-97 B Bacteria, 46 Balard, Antoine, 55 Barium, 30-31 X-ray photography and, 31 Barium meal, 31 Barium sulfate, 31 Base, 20, 146 Bauxite, 34 Becquerel, Henri, 61 Benzene, 18, 74-75 Berg, Otto, 43 Beryllium, 30, 31 Berzelius, Jons, 39, 43, 53 Biochemical energy, 116-121 Biochemistry, 10, 104-105, 106-125, 146 Biogas, 69 Biotechnology, 124-125 Bismuth, 48, 49 Bluejohn, 55 Borax, 34 Borazon, 34 Boron, 34, 35 Boron group, 34-35 Boyle, Robert, 49 Brand, Hennig, 49 Brandt, Ceorg, 41 Brass, 28 Bromine, 54, 55 Bronze, 28, 32 Bunsen, Robert, 27 Bussy, Antoine, 31 c Cadmia, 33 Cadmium, 32, 33 Cadmium sulfide, 33 Calcium, 30-31 Calcium carbonate, 30 Calcium salts, 30 Calvin cycle, 121 Carbohydrate, 107, 146 Carbon, 36-37 amorphous, 36, 37 inorganic, 36-37 Carbon black, 36, 72 Carbon dioxide, 36 Carbonyl group, 65, 146 Carboxylic acid, 85, 146 Catalysis, 20, 146 Catalyst, 40, 105, 132, 146 Cation, 20, 146 Cavendish, Henry, 25 Cellulose, 102, 103, 146 Cerium, 59 Cesium, 27 Chelating agent, 95, 146 Chemical analysis, 142-143 clinical, 142 food and drug, 142 forensic, 142, 143 pollution control, 142 quality control, 142-143 Chemical bond, 14-15, 75 coordinate, 14, 15, 147 covalent, 14, 146 ionic, 14, 15, 148 Chemical equilibrium, 20 Chemical reduction, 20 Chemical symbol, 14-15 Chemistry analytical, 126-143, 146 biological sciences, 10 civilization, 11 detection techniques, 126-127 history, 8-11 organic, 66-103, 149 separation techniques, 126, 127 Chlorine, 54, 55 Chlorofluorocarbons, 79 Chlorophyll, 89-90, 120, 146 Cholesterol, 109, 122 Chromatography, 136, 146 column, 136 descending paper, 137 gas, 137 paper, 137 thin-layer, 136-137 two-phase, 137 Chromite, 40 Chromium, 40, 41 Cinnabar, 33 Citric acid cycle see Krebs cycle Cluster compound, 65 Cobalt, 40-41 Color, 96-97 Combustion, 19 Complex organic compounds, 94-95 Continuous flow analyzer, 141 Coordination compounds, 64 Copper, 28, 29, 32, 41 Coster, Dirk, 43 Courtois, Bernard, 55 Covalent bond, 13 Crawford, Adair, 31 Crick, Francis, 10, 114 Cronstedt, Axel, 41 Crookes, William, 35 Cupronickel, 28 Curie, Marie, 31, 53, 61 Curie, Pierre, 31, 53, 61 D Dalton, John, 8-9, 146 Davy, Humphry, 27, 35 Debierne, Andre, 61 de Boisbaudran, Paul Emile Lecoq, 35 de Elhuyar, Fausto, 43 de Elhuyar, Juan, 43 de Ulloa, Antonio, 55 Deoxyribonucleic acid (DNA), 114-115, 125, 147 Deuterium, 12, 25 Diamond, 36, 37 Differential thermal analysis (DTA), 134 Digester, 69 Digitoxin, 67 DNA see Deoxyribonucleic acid D orbital, 12,23 Dorn, Friedrich, 57, 61 Double decomposition, 20 Drugs, 95 Dye, 96, 98, 99 E Ekeberg, Anders, 43 Electrolysis, 16, 18, 28, 34, 147 Electron, 12-13, 147 carriers, 117 cloud, 75 shell, 22,23, 150 Electron spin resonance (ESR), 131 Electronic spectra, 131 Electrophoresis, 139 Elements, 12-13, 147 chemical, 21 classifying, 22 major groups, 23 periodic table, 22 quantum numbers, 23 rare earth, 58-59 transition, 15, 151 Emission spectroscopy, 130 Enzymes, 112-113, 147 Epinephrine, 122, 123 Epoxides, 81 Epsom salt, 30 Esterification, 81, 86, 147 Esters, 86-87 Ethanol, 80-81 Ethene, 73 Ethers, 81 Ethyne, 73 F Faraday, Michael, 18 Ferrocene, 93 Flame test, 128 Flavones, 96 Index 153
G Cadolin, )ohan, 126 Gahn, Johan, 41 Galena, 38, 39 Gallium, 34, 35 Galvanized steel, 32 Gay-Lussac, Joseph, 35 Gene, 10, 114-115, 148 deoxyribonucleic acid (DNA), 114-115, 125, 147 genetic engineering, 124-125 molecular genetics, 10 mutations, 115 ribonucleic acid IRNA), 114-115, 150 Germanium, 38, 39 Glycerol, 81 Glycolysis, 117-118 Gold, 28, 29 Gold leaf, 29 Graphite, 36, 37, 77 Gravimetry, 129 Gregor, William, 41 H Haber-Bosch process, 47 Hafnium, 40, 41,42, 43 Halogen, 54-55, 66, 78, 148 Halogenation, 70 Hatchett, Charles, 43 "Heavy hydrogen," 12, 25 Helium, 56-57 Hemoglobin, 110, 111 Hjelm, Peter, 43 Hormone, 122, 123, 124, 148 Hydrazine, 46-47 Hydrocarbons, 148 aromatic, 74-77 cancer-causing properties, 77 condensed aromatic, 76, 77 cyclic, 70-71, 146 halogenated, 78-79 long-chain, 71 saturated aliphatic, 72 unsaturated aliphatic, 72-73 Hydrogen, 24-25, 47 bomb, 24, 25 bond,147 carriers, 117 compounds and uses, 24-25 isotopes, 25 properties, 24 Hydrogenation, 25 I llmenite, 40 Indium, 34, 35 Infrared spectrometer, 130 Inhibition, 113, 148 Ink, 97 Inorganic carbon, 36-37 Inorganic compounds, 64-65 Instrumental analysis emission spectroscopy, 130 focusing mass spectrograph, 133 gravimetry, 129 infrared spectrometer, 130 liquid chromatography, 138 mass spectrometry, 138 preparative chromatography, 138 radiochemical analysis, 133 resonance spectroscopy, 131 spectrophotometer, 132 spectroscopic analysis, 130-131 titrimetry, 129 volumetric analysis, 129 Iodine, 54, 55 Ions, 15,20 complex, 64-65 hydrogen, 117 monodentate, 64-65 negative, 15 positive, 15 Iridium, 43, 44, 45 Iron, 40, 41, 62 Isomer, 14, 69 Isomerism, 15, 68, 148 Isotope, 12,31, 147 astatine, 54 carbon, 37 cobalt, 41 hydrogen, 25 polonium, 53 radioactive, 133 radon, 57 Date: 2015-12-11; view: 1093
|
In the following glossary, small capital letters (for example, radiation) indicate terms that have their own entries in the glossary.
146 Glossary
gen atoms in ammonia has been replaced by an organic group, such as an alkyl group. See also organic
substance dissolved in another liquid. Concentration is also used to mean the act of making a solution more concentrated. condensation reactionA chemical reaction in which two molecules link together, usually with the expulsion of a small molecule, such as water or ammonia. See
148 Glossary
geneA short length of DNA that contains the genetic code for the manufacture of a particular protein. In most organisms, genes are strung together into longer DNA units called chromosomes. See also deoxyribonucleic ACID.
ligandAn atom or group of atoms that forms complex compounds by establishing a coordinate bond with the ion of a metal. The ion is the central atom of a complex. The ligands surround the ion. See also compound; lone
are influenced by light as an energy source, photosynthesis and the exposure of photographic film or paper are examples of this type of chemical reaction.
vaccineA preparation which, when introduced into the bloodstream, causes the production of an antibody. Vaccines are produced from weakened strains of the infectious microorganism that the antibody is meant to fight. Vaccines can also be produced from dead cells of the microorganism.
A
Flavonols, 96 Fluorides, 54 Fluorine, 54 Food colorant, 97 Formalin, 83 Francium, 27 Frasch method, 52 Fusion method, 24