Inorganic Chemistry - chemistry.

Inorganic Chemistry - chemistry. I INTRODUCTION Inorganic Chemistry, study of the structure, properties, and reactions of the chemical elements and their compounds. Inorganic chemistry does not include the investigation of hydrocarbons--compounds composed of carbon and hydrogen that are the parent material of all other organic compounds. The study of organic compounds is called organic chemistry. Inorganic chemists have made significant advances in understanding the minute particles that compose our world. These particles, called atoms, make up the elements, which are the building blocks of all the compounds and substances in the world around us. Just as the entire English language is constructed from combinations of the 26 letters in the alphabet, all chemical substances are made from combinations of the 112 chemical elements found on the periodic table (see Periodic Law). Ninety elements are known to occur in nature, and 22 more have been made artificially. Elements--which include substances such as oxygen, nitrogen, and sulfur--cannot be broken into more elementary substances by ordinary chemical means. The elements are arranged in the periodic table in rows from the lightest element (hydrogen) to the heaviest (ununbium). These rows are split so that elements with similar chemical properties fall in the same columns (for more information, see the Periodic Law section of this article). The smallest representative unit of an element is an atom (see Atom). (For example, the smallest representative of the element helium (He) is a helium atom.) When atoms that come in close contact have a sufficiently large attractive force, a chemical bond, or binding link, forms between them. The combination of two or more atoms bonded together is called a molecule. A molecule is the smallest particle of a substance possessing the specific chemical properties of that substance. For example, an atom of oxygen (O) combines with two atoms of hydrogen (H) to form a water molecule (H2O). While molecules of H2O possess the properties of water, individual oxygen and hydrogen atoms do not. Much of chemistry can be described as breaking substances apart and putting chemical components together to form new substances. This process is accomplished by breaking chemical bonds between atoms and creating new bonds, a process known as a chemical reaction. II IMPORTANT INORGANIC COMPOUNDS Advances in inorganic chemistry have made significant contributions to modern living. For instance, synthetic fertilizers manufactured from inorganic chemicals have increased worldwide crop production. Inorganic substances used to fabricate silicon chips help power the global information age. Engineers use metal alloys in automobiles and aircraft to make them lighter and stronger. Companies also use inorganic compounds to fabricate concrete, steel, and glass--materials used to construct buildings, infrastructure, and other public works around the world. In the United States, 10 of the 11 most commonly produced chemicals are derived from inorganic elements. These 10 inorganic chemicals (presented below in descending order of production) are used in a wide variety of applications. Sulfuric acid (H2SO4) is used to make fertilizers, synthetic fibers, and metals. Nitrogen (N2) is used in recovering underground petroleum deposits, in the production of ammonia (NH3), and as a blanketing material for shipping perishables such as fruits and vegetables. Oxygen (O2) is used in the production of steel and plastics, in medical applications, and in rocketry. Lime (CaO) is used in the manufacture of steel and cement. Ammonia (NH3) is combined with sulfuric acid to make ammonium sulfate (NH4SO4), the most important of the synthetic fertilizers. The remaining five most commonly produced inorganic chemicals (which frequently interchange rankings in production volume) are also used in a wide variety of applications. Sodium hydroxide (NaOH), commonly called lye, is used in the manufacture of paper, soap, detergents, and synthetic fibers, and is also a caustic material used as a drain cleaner. Chlorine (Cl2) is used to manufacture vinyl chloride plastic, to disinfect drinking water, and to bleach paper during manufacturing. Phosphoric acid (H3PO4) is used to give soft drinks a tart flavor and to make fertilizers. Sodium carbonate (Na2CO3), more commonly known as soda ash, is used in the production of glass, paper, and textiles. Nitric acid (HNO3) is used to make synthetic fibers, such as nylon; explosives, such as nitroglycerin and TNT (trinitrotoluene); and is also combined with ammonia to make fertilizer. III PERIODIC LAW Modern inorganic chemistry can be traced to the work of Russian chemist Dmitry Ivanovich Mendeleyev and German physicist Julius Lothar Meyer, who independently developed the periodic law of the chemical elements at about the same time in the late 19th century. Mendeleyev is generally credited with the findings, because he established the periodic law in 1869, and Meyer established this chemical law a year later. Both scientists, however, discovered that arranging the elements in order of increasing atomic mass produced a table of chemical properties and reactivity patterns that were regularly repeated. This phenomenon--known as the periodic law--is most often represented in the periodic table of the elements. By arranging the elements into rows of increasing atomic mass, Mendeleyev observed that elements with similar properties fell into the same vertical columns, called groups. For example, members of the alkali metals--lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs)--are all are extremely reactive, bursting into flames when they are brought in contact with water. IV STRUCTURE OF THE ATOM Building on Mendeleyev's work, scientists sought to explain the periodic law by understanding the structure of the atom. Through various experiments, scientists discovered that atoms consist of three types of subatomic particles--electrons, protons, and neutrons. Electrons are small, negatively charged particles that orbit a dense core in the atom called the nucleus. The nucleus is composed of the larger, positively charged protons and neutral neutrons. The attractive force between the oppositely charged electrons and protons holds the orbiting electrons around the nucleus. Ordinarily, atoms contain an equal number of protons and electrons, creating electrically neutral atoms. A Electrons British physicist Joseph Thomson discovered the electron in 1898 by experimenting with cathode rays--unexplained rays or beams produced by conducting electricity through a vacuum tube. Thomson used magnetic and electric fields to bend the path of the beam inside the vacuum tube. By adjusting the strength of these fields, he was able to control the deflection of the beam. From these measurements, Thomson determined that the cathode ray particles carried a negative charge, and he was able to calculate the charge-to-mass ratio of the particles. Thomson accurately hypothesized that these negatively charged particles, which later became known as electrons, are part of all matter found in nature. In 1909 American physicist Robert Millikan determined the charge and mass of individual electrons by measuring the rate that oil drops laden with electrons fell between two electrically charged plates (positively charged top plate and negatively charged bottom plate). By measuring the difference in how fast these electron-laden oil drops fell when the metal plates were charged and uncharged, Millikan was able to calculate the total charge on each oil drop. Because each measurement was a whole number multiple of -1.60 × 10-19 coulombs, Millikan concluded this was the charge carried by a single electron. Using Thomson's electron charge-to-mass ratio, Millikan then calculated the mass of a single electron to be approximately 9.109 × 10-28 grams. In 1913 Danish physicist Niels Bohr developed a theoretical model of the hydrogen atom. Bohr proposed that electrons moving around the nucleus remain in certain quantifiable orbits called orbitals. These orbitals are similar to the paths of the planets orbiting around the sun. Bohr's research further revealed that the electron orbitals correspond to fixed energy levels, or shells, similar to the layers of an onion. Each energy level may include several different orbitals (see Atom: Bohr Atom). In 1925 Austrian-born physicist Wolfgang Pauli proposed his exclusion principle, lending considerable understanding to the complex behavior of electrons in the atom. Pauli's exclusion principle states that each orbital within an energy shell can hold a maximum of two electrons, and that when two electrons occupy the same orbital, these electrons will have opposite spins about their own axis. Spin is a property of angular momentum that all electrons possess. In 1926 Austrian physicist Erwin Schrödinger applied the wave properties of matter to the arrangement of electrons within the atom. This work, known as quantum theory, models the configuration and the increasing number of orbitals contained in each successive shell moving away from the nucleus. In general, electrons fill the lowest-energy shells first. Once a lower-energy shell is filled, electrons begin filling the next highest energy level. B Protons In the early 1900s, Thomson also proved that positively charged particles are a fundamental part of the atom. Thomson used a modified cathode-ray tube filled with hydrogen gas. By passing a spark through the gas, he was able to bump the electrons off of the hydrogen atoms, leaving particles known as ions. Thomson accelerated the hydrogen ions through an electric field and observed that the ions deflected toward the negatively charged electrode (electric conductor). As a result, Thomson correctly concluded that hydrogen ions contain positively charged particles; these particles are now referred to as protons. Experiments using an instrument known as a mass spectrometer revealed that protons have a mass roughly 1800 times greater than that of electrons. The mass spectrometer also showed that each element is differentiated by the number of protons it contains (known as the atomic number). The elements are arranged in the periodic table by increasing atomic number. For example, hydrogen has one proton, helium has two, and lithium has three. C Nucleus and Neutrons In the early 1900s, British physicist Ernest Rutherford discovered both the nucleus of the atom and neutrons. He conducted experiments that shot positively charged subatomic particles through metal foil. Rutherford observed that nearly all the subatomic particles passed straight through the foil, while a few were deflected at large angles. From these observations, Rutherford concluded that each atom in a metal foil must have an extremely dense core, or nucleus, deflecting the few particles that come near it. This core is surrounded by a much greater volume of empty space, which allows most particles to pass through. From the large angles of deflection, Rutherford concluded that the nucleus was positively charged and that it repelled the subatomic particles. By measuring these angles, he was also able to estimate the number of protons in the nucleus. However, because the mass of the protons accounted only for half the weight of the nucleus, Rutherford hypothesized that an equal number of neutrally charged particles must also compose the nucleus. These particles were later named neutrons. V CHEMICAL BONDS Seeking to explain how atoms in elements combine to form molecules, American chemists Gilbert Lewis and Irving Langmuir developed the theory of electron valence in 1916. They proposed that chemical bonds form between electrons residing in the outermost, or valence, shell of each bonding atom. When two atoms share a pair of valence electrons, they form a chemical bond. The Langmuir-Lewis theory provided insight into Mendeleyev's periodic law by stating that an element's reactivity is largely determined by the number of electrons in the outer shell of its atoms. Because elements in the same group (or column) on the periodic table all have an equal number of valence electrons, the Langmuir-Lewis theory explains why elements within each group share similar reactivities and properties. Moving left to right across the periodic table, element groups have increasingly filled outer shells. For example, Group 1 elements (alkali metal elements) each contain only a single valence electron, while Group 18 elements (noble gases) have completely filled outer shells. As a result, the alkali metal elements are extremely reactive, and the noble gases are extremely stable and unreactive, or inert. Twentieth-century scientists observed that in order to achieve the energetic stability of the noble gases, elements seek to fill their outer shell with electrons. To become more energetically stable, atoms often borrow or share electrons from other atoms, forming ionic or covalent chemical bonds. A Ionic Bonds Atoms form ionic bonds when they gain or lose electrons and subsequently become electrically charged. An atom that gains an electron is known as a negative ion, and an atom that loses an electron is known as a positive ion. Ionic bonds form between elements having atoms that are close to completing their valence shell and elements having atoms that hold few electrons in their valence shell. For example, chlorine (Cl) is only one electron short of filling its valence shell, so it has a strong affinity for electrons. It can easily pull an electron away from sodium (Na), which only has one loosely held valence electron. As a result of this electron exchange, two ions form: a negative chlorine ion (Cl-), and a positive sodium ion (Na+ ). These oppositely charged ions attract each other, combining in equal proportions to form common table salt: Na+ + Cl- -> NaCl. B Covalent Bonds Covalent bonds form between atoms that have a tendency to share valence electrons to complete their outer shell. Such atoms form electrically neutral groups of atoms called molecules. Many familiar substances are composed of molecules. Oxygen atoms are two electrons short of filling their outer shell. Oxygen bonds with two hydrogen atoms (each possessing a single electron) to form water (H2O). Chlorine (Cl), which is one electron short of filling its outer shell, shares a valence electron with another chlorine atom to form Cl2, thereby filling the outer shells of both atoms. Nitrogen (N), which is three electrons short of filling its outer shell, bonds with three hydrogen atoms to form ammonia (NH3). Most bonds that occur in compounds are actually a combination of covalent and ionic bonding. Generally, however, bonds in which one or more electrons remain with one atom for most of the time are called ionic, while bonds in which the electrons are equally shared for most of the time are called covalent. VI CHEMICAL REACTIONS Chemical reactions are processes by which atoms or molecules are redistributed, resulting in different substances with unique properties. Many industries rely on largescale chemical reactions to make products, such as alloys, fertilizers, and building materials (including glass and concrete), that are vital to modern life. Chemical reactions are classified into different categories according to the mechanics of the reactions. The original elements or compounds involved in a chemical reaction are called reactants, and the chemicals that result are called products. A Combination and Decomposition Reactions Combination reactions follow the simple formula: A + B = C, where A and B are elements or compounds that combine to form the new compound C. For example, aluminum (Al) combines rapidly with molecular oxygen (O2) to form aluminum oxide (Al2O 3): 4Al + 3O2 -> 2Al2O 3 The numbers before each formula refer to the relative amounts of each element or compound in the reaction. Aluminum oxide forms a protective layer over aluminum products such as soda cans and foil, preventing further oxidation of the metal. In contrast, iron is poorly protected by its oxide layer and subsequently rusts with exposure to air. Another combination reaction occurs when sulfur (S) reacts with molecular oxygen to form gaseous sulfur dioxide (SO2): S(s) + O2(g) -> SO2(g). The letter subscripts in the equation refer to the physical states of the reactants and product--s stands for solid, g stands for gas, and an l would stand for liquid. A decomposition reaction is the reverse of a combination reaction. For example, when solid potassium chlorate (KClO3) is heated, it decomposes into molecular oxygen and potassium chloride (KCl): 2KClO3(s) -> 3O2(g) + 2KCl(s). The oxygen product of this decomposition reaction is useful for applications such as medical emergencies. Another decomposition reaction is the rapid decay when exposed to light of silver iodide (AgI) into silver (Ag) and iodine (I): 2AgI -> 2Ag + I2. B Oxidation-Reduction Reactions Oxidation-reduction, or redox, reactions combine chemicals wanting to gain electrons (or be reduced) with chemicals that are willing to give up electrons (or be oxidized). For example, sodium (Na), with its single loosely held valence electron, gives up its outer electron (or is oxidized) by sulfur (S) to form sodium sulfide (Na2S): 2Na + S -> Na2S. In this redox reaction, two sodium atoms each give up an electron to fill the sulfur atom's outer shell. Each of the sodium atoms are subsequently oxidized to form positive ions (Na+ ), while the sulfur atom is reduced to a negative ion (S-2). These oppositely charged ions combine to form sodium sulfide. See Chemical Reaction. C Acid-Base Reactions An acid-base reaction occurs when a strong acid--a substance capable of donating hydrogen ions (H+ )--reacts with a strong base--a substance capable of accepting hydrogen ions (see Acids and Bases). Acid-base reactions produce water and a salt. Salts are defined in chemistry as ionic compounds where the cation (positive ion) is not H+ and the anion (negative ion) is not O2- or OH-. For example, hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to produce sodium chloride (NaCl), which is a salt compound, and water: HCl + NaOH -> NaCl + H2O. D Displacement Reactions Displacement reactions cause elements to displace each other from a compound. For example, magnesium (Mg) displaces titanium (Ti) in the following reaction: 2Mg + TiCl4 -> Ti + 2MgCl2. Manufacturers use this particular displacement reaction to extract titanium, valued for its strength and light weight by the aerospace and other industries, from the compound titanium tetrachloride (TiCl4). E Exchange Reactions Exchange reactions are driven by compounds wanting to exchange ions in order to form more stable products, namely acids or salts. For example, titanium tetrachloride (TiCl4) reacts violently with water as TiCl4 exchanges one titanium ion (Ti+4) for every four hydrogen ions (H+ ) in the water: TiCl4(g)+ 2H2O (g) -> 4HCl(g) + TiO2(s). This reaction produces hydrochloric acid (HCl) and titanium dioxide (TiO2). Titanium dioxide typically occurs in mineral deposits as an impure black substance. Chlorinating titanium oxides from mineral compounds produces TiCl4. Because titanium dioxide is needed as the major pigment in white paint, manufacturers use the above exchange reaction to isolate titanium dioxide from TiCl4. VII FACTORS INFLUENCING REACTIONS Chemical reactions occur when certain physical and chemical factors make conditions energetically favorable for the reactants to combine into products (see Thermodynamics). Some factors, such as the potential energy (stored energy) associated with the reactants, can trigger a spontaneous chemical reaction. If the products have a higher level of entropy (disorder among the particles) than the reactants, this difference can also initiate a chemical reaction. External factors, such as heat or the presence of a catalyst (a substance that increases reaction rate without being chemically changed), can trigger or increase the rate of a reaction (see Catalysis). A Exothermic and Endothermic Reactions Chemical reactions can occur spontaneously if the reactants possess more potential energy (stored energy) than the products. This type of reaction occurs spontaneously because of the downhill energy path (from more potential energy to less). These reactions are called exothermic (heat-producing) reactions, because potential energy is converted to heat as the reactions proceed. Conversely, endothermic (heat-absorbing) reactions do not occur spontaneously because of the uphill energy path that exists. The products of endothermic reactions contain more potential energy than the reactants. As a result, energy must be added to trigger an endothermic reaction. B Entropy Entropy is the tendency for matter to become disordered. Nature requires the input of energy to maintain an ordered state--a bedroom will become messy if not periodically cleaned; a car will eventually fall into disrepair if not regularly serviced. Entropy is an important force in chemistry. If other factors influencing a reaction are held equal, a chemical reaction will proceed spontaneously if the products have higher entropy (are more disordered) than the reactants. This law explains why ozone (O3) gas can spontaneously decompose into molecular oxygen (O2): 2O3(g) -> 3O2(g). This reaction occurs because the molecular order is diminished, resulting in a higher level of entropy. C Heat Applying heat to matter in the solid, liquid, or gas phase adds energy to the substance, causing the atoms to move faster and collide into each other with greater force. As a result, heat speeds up a chemical reaction by bringing atoms into contact with each other with greater force and frequency. D Catalysts Catalysts are substances that trigger or speed up chemical reactions (without chemically altering the catalysts in the process). A catalyst combines with a reactant to form an intermediate compound that can more readily react with other reactants. An example of this is the formation of sulfur trioxide (SO3), which is an important ingredient for producing sulfuric acid (H2SO4). Without a catalyst, sulfur trioxide is made by combining sulfur dioxide (SO2) with molecular oxygen: 2SO2 + O2 -> 2SO3. Because this reaction proceeds very slowly, manufacturers use nitrogen dioxide (NO2) as a catalyst to speed production of SO3: Step One: NO2 (catalyst) + SO2 -> NO + SO3 (SO3 is extracted and combined with steam to produce sulfuric acid) Step Two: NO (from Step One) + O2 -> NO2 (catalyst that is reused in step one) In the above reactions, nitrogen dioxide (NO2) acts as a catalyst by combining with sulfur dioxide (SO2) to form both sulfur trioxide (SO3) and nitrogen monoxide (NO). The sulfur trioxide is removed from the process (to be used in the production of sulfuric acid). Nitrogen monoxide (NO) is subsequently combined with molecular oxygen (O2) to produce the original catalyst, nitrogen dioxide (NO2), which can be continually reused to catalyze sulfur trioxide (SO3). VIII NAMING INORGANIC COMPOUNDS Scientists have established a system of rules for naming most inorganic substances. A Elements The names of metals generally end in -ium or -um (examples are sodium, potassium, aluminum, and magnesium). The exceptions are metals that were used and named in ancient times, such as iron, copper, and gold. The names of nonmetals frequently end in -ine, -on, or -gen (such as iodine, argon, and oxygen). Given the names of the constituent elements and common ions, most of the common inorganic compounds can be named using the rules presented below. B Acids The names of acids without oxygen in the molecule have the prefix hydro- (sometimes shortened to hydr-) and the suffix -ic attached to the stem based on the names of the constituent elements (other than hydrogen). For example, HCl (made of hydrogen and chlorine) is hydrochloric acid; HBr (made of hydrogen and bromine) is hydrobromic acid; HI (made of hydrogen and iodine) is hydroiodic acid; HCN (made of hydrogen, carbon, and nitrogen) is hydrocyanic acid; and H2S (made of hydrogen and sulfur) is hydrosulfuric acid. Names of acids containing oxygen (known as oxoacids) are derived from the number of oxygen atoms in the molecules of a series, or class, of acids. An example of an oxoacid series is as follows: HClO, HClO2, HClO3, HClO4. If a class of acids contains only one member, its name is given the suffix -ic. For example, H2CO3 is carbonic acid. If an acid series contains two acids, such as H2SO4 and H2SO3, the acid containing more oxygen atoms is given the suffix -ic, while the acid with fewer oxygen atoms is given the suffix -ous. For example, H2SO4 is sulfuric acid, and H2SO3 is sulfurous acid. Similarly, HNO3 is nitric acid, and HNO2 is nitrous acid. In the case of an extensive acid series (such as HClO, HClO2, HClO3, HClO4), the acid with the fewest oxygen atoms is given the prefix hypo- and the suffix -ous, and the acid with the most oxygen atoms is given the prefix per-. In the above example, HClO is hypochlorous acid, HClO2 is chlorous acid, HClO3 is chloric acid, and HClO4 is perchloric acid. C Positive Ions Names of positive ions end in -ium if the ion has only one oxidation state (only one level of net charge). For example, the positive ion of ammonia is NH4+ (ammonium), and the positive ion of water (H2O) is H3O + or H+ (hydronium). If two oxidation states (two levels of net charge) exist for the positive ion of an element, the less positive ion ends in -ous, and the more positive ion ends in -ic. For instance, the two positive ions of copper are Cu+ (cuprous) and Cu2+ (cupric). The oxidation state of a positive ion can also be designated by placing a Roman numeral after the name of the element. These positive ions of copper can also be written as copper (I) and copper (II), respectively. D Negative Ions Names of negative ions from oxygen-deficient acids (for more information, see the Acids section of this article) end in -ide. For example, Cl- (chloride) from HCl, and CN- (cyanide) from HCN. Names of negative ions derived from acids with the -ous prefix end in -ite. For example, NO2- (nitrite) is derived from HNO2 (nitrous acid), and SO32- (sulfite) is derived from H2SO3 (sulfurous acid). E Salts Salts are named for the ions that compose them. The cation (positively charged ion) within the compound is named first. Examples are NaCl (sodium chloride), BaO (barium oxide), Fe(NO3)2 [iron (II) nitrate], and Fe(NO3)3 [iron (III) nitrate]. F Covalent Compounds If two elements form a covalent compound, the prefixes di-, tri-, tetra-, penta-, hexa-, and so on, are used to indicate the number of atoms. Examples of covalent compounds include CS2 (carbon disulfide), PCl5 (phosphorus pentachloride), and N2O 4 (dinitrogen tetroxide). IX FIELDS OF INORGANIC CHEMISTRY Inorganic chemistry, which is the study of the structure and reactivity of inorganic compounds, overlaps with other branches of chemistry, such as physical chemistry and analytical chemistry. Physical chemists develop and use instruments to probe the physical properties (such as density, viscosity, and crystallography) of compounds as well as the behavior of chemical systems. Analytical chemists work to determine the unknown chemical constituents of substances and the relative amounts of these constituents. Inorganic chemistry is often divided into the subfields of solid-state chemistry, organometallic chemistry, and bioinorganic chemistry. While solid-state chemistry stays more within the bounds of traditional inorganic chemistry research, organometallic chemistry and bioinorganic chemistry overlap with organic chemistry and biology, respectively. Research in solid-state chemistry, organometallic chemistry, and bioinorganic chemistry is leading to progress in areas such as superconductivity, microchip development, and cancer research. A Solid-State Chemistry Solid-state chemists study the structure and properties of inorganic compounds to fabricate new, more useful materials. For example, solid-state chemists are working to develop high-temperature pliable ceramics capable of withstanding temperatures up to 1370° C (2500° F). These high-temperature ceramics may someday be used to make automobile engines that produce little pollution and are highly fuel-efficient. High-temperature ceramics might also be used someday as superconductors--materials that exhibit no resistance to electric current. Superconductors made from hightemperature ceramics might be used in supercomputers (powerful computers used to solve extremely complex problems), in medical diagnostic equipment such as magnetic resonance imaging (MRI), and to transmit electricity without loss of electrical power. Inorganic chemists are making rapid advances in the development of new inorganic polymers. Polymers are usually large, organic molecules that make up substances such as proteins, rubber, and plastics. Most plastics consist of organic polymers made up of extremely long carbon chains. Current research has produced inorganic polymers known as polyphosphazenes, which consist of long chains of alternating nitrogen and phosphorus atoms. Polyphosphazenes may eventually be used in the medical field to provide materials for artificial blood vessels, limbs, and joints. Chemists have found that changing the side groups of atoms attached to these nitrogen-phosphorus chains forms plastics that possess unique properties, such as the ability for a plastic pill capsule to time-release ingested drugs into the circulatory system. Another inorganic polymer, polysulfurnitride, consists of alternating sulfur and nitrogen atoms. This polymer conducts electricity and becomes a superconductor at the temperature of -273° C (-460° F). However, because polysulfurnitride is unstable, it is not currently used in practical applications. B Organometallic Chemistry An extremely active area of research in recent years is the study of organometallic chemicals--compounds that consist of transition metals bonded to organic chemical groups. Examples of organometallic complexes include iron pentacarbonyl [Fe(CO)5], ferrocene [Fe(C5H5)2], and phenylmagnesium bromide (C6H5MgBr). Organometallic compounds are used to produce semiconductor wafers, to form highly protective coatings on steel tools (such as high-speed drills), and as extremely selective catalysts in certain organic compound syntheses. C Biological Inorganic Chemistry Biological inorganic (bioinorganic) chemists research the role of metals in living systems. One area of investigation is the role of metals in the human body, such as how oxygen binds reversibly to the iron in red blood cells. Bioinorganic chemists also study how specific transition metals might be used in drugs to fight certain diseases. For example, scientists are experimenting with platinum complexes as anticancer drugs. Contributed By: Richard B. Kaner Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.