Definition of Inorganic Chemistry
Inorganic chemistry is concerned with the properties and behavior of inorganic compounds, which include metals, minerals, and organometallic compounds. It deals with the synthesis and behavior of inorganic and organometallic compounds. And covers all chemical compounds except the myriad organic compounds (carbon-based compounds), which are the subjects of organic chemistry.
In simple words, it is opposite to that of Organic Chemistry. The substances which do not have carbon-hydrogen bonding are the metals, salts, chemical substances, etc. On this planet, there are known to exist about 100,000 number of inorganic compounds. Inorganic chemistry studies the behavior of these compounds along with their properties, their physical and chemical characteristics too. The elements of the periodic table except for carbon and hydrogen, come in the list of inorganic compounds. Many of the elements are technologically important: titanium, iron, nickel and copper, for example, are used structurally and electrically. Second, the transition metals form several useful alloys, with each other and with other metallic elements.
A common differentiation to help distinguish between inorganic compounds. And organic compounds is that inorganic compounds are either the result of natural processes. Unrelated to any life form or the result of human experimentation in the laboratory. Whereas organic compounds result from the activity of living beings. Another definition pertains to the salt-making property of inorganic compounds, which is absent in organic compounds.
Many inorganic compounds are ionic compounds, consisting of cations and anions joined by ionic bonding.
Examples of salts (which are ionic compounds) are :
magnesium chloride MgCl2, which consists of magnesium cations Mg2+ and chloride anions Cl– or sodium oxide Na2o, which consists of sodium cations Na2+ and oxide anions O2-. In any salt, the proportions of the ions are such that the electric charges cancel out. So that the bulk compound is electrically neutral. The ions are described by their oxidation state and their ease of formation can be inferred from the ionization potential (for cations) or from the electron affinity (anions) of the parent elements.
Important classes of inorganic compounds are the oxides, the carbonates, the sulfates, and the halides. Many inorganic compounds are characterized by high melting points. Inorganic salts typically are poor conductors in the solid state. Other important features include their high melting point and ease of crystallization. Where some salts (e.g., NaCl) are very soluble in water, others (e.g., FeS) are not.
The simplest inorganic reaction is double displacement when in mixing of two salts. The ions are swapped without a change in oxidation state. In redox reactions one reactant, the oxidant, lowers its oxidation state. And another reactant, the reductant, has its oxidation state increased. The net result is an exchange of electrons. Electron exchange can occur indirectly as well, e.g. in batteries, a key concept in electrochemistry.
When one reactant contains hydrogen atoms, a reaction can take place by exchanging protons in acid-base chemistry. In a more general definition, any chemical species capable of binding to electron pairs is called a Lewis acid; conversely any molecule that tends to donate an electron pair is referred to as a Lewis base. As a refinement of acid-base interactions, the HSAB theory takes into account polarizability and size of ions.
Inorganic compounds are found in nature as minerals. Soil may contain iron sulfide as pyrite or calcium sulfate as gypsum. Inorganic compounds are also found multitasking as biomolecules. As electrolytes (sodium chloride), in energy storage (ATP) or in construction (the polyphosphate backbone in DNA).
The first important man-made inorganic compound was ammonium nitrate for soil fertilization through the Haber process. Inorganic compounds are synthesized for use as catalysts such as vanadium(V) oxide and titanium(III) chloride, or as reagents in organic chemistry such as lithium aluminum hydride. Subdivisions of inorganic chemistry are organometallic chemistry, cluster chemistry and bioinorganic chemistry.
An alternative perspective on the area of inorganic chemistry begins with the Bohr model of the atom. And using the tools and models of theoretical chemistry and computational chemistry, expands into bonding in simple and then more complicated molecules. Precise quantum mechanical descriptions for multielectron species, the province of inorganic chemistry, is difficult. This challenge has spawned many semi-quantitative or semi-empirical approaches including molecular orbital theory. And ligand field theory, In parallel with these theoretical descriptions, approximate methodologies are employed, including density functional theory.
Exceptions to theories, qualitative and quantitative, are extremely important in the development of the field. For example : Cu2(OAc)4(H2O)2 is almost diamagnetic below room temperature whereas crystal field theory predicts that the molecule would have two unpaired electrons. The disagreement between qualitative theory
(paramagnetic) and observation (diamagnetic) led to the development of models for magnetic coupling, such as the exchange interaction. These improved models led to the development of new magnetic materials and new technologies.
Although some inorganic species can be obtained in pure form from nature. Most are synthesized in chemical plants and in the laboratory. Inorganic synthetic methods can be classified roughly according to the volatility or solubility of the component reactants. Soluble inorganic compounds are prepared using methods of organic synthesis.
For metal-containing compounds that are reactive toward air, Schlenk line and glove box techniques are followed. Volatile compounds and gases are manipulated in “vacuum manifolds” consisting of glass piping interconnected through valves. The entirety of which can be evacuated to 0.001 mm Hg or less. Compounds are condensed using liquid nitrogen (b.p. 78K) or other cryogens.
Solids are typically prepared using tube furnaces, the reactants and products being sealed in containers, often made of fused silica (amorphous SiO2 ). But sometimes more specialized materials such as welded Ta tubes or Pt “boats”. Products and reactants are transported between temperature zones to drive reactions.
Metals serve an essential role in many aspects of human civilization and have defined Ages of human history. The period of the time from about 3300BC to 1200BC is often referred to as the Bronze Age. During this period our ancestors first started using metal and learned to mix various elements with copper to make a strong alloy, called bronze. This age yielded significant advancement in crafting of sharper knives and stronger weapons out of metal instead of rock, wood and bone. Around 1200 BC the human race found an even harder metal and discovered a much stronger alloy called steel.
This period is known as the Iron Age. Most recently, periods of time known as Gold Rushes have caused huge changes in population distributions and wealth in some countries. Metal has obvious importance in our modern way of the life. Today, iron and steel are used for making buildings, machines, automobiles, jewelry, cooking, pots, tools, weapons, vehicles, electronics, surgical instruments and symbolic structures like the Eiffel Tower and the Statue of Liberty. Gold, silver and copper still serve as currency for trade and exchange of goods and services.
The existence of Chemistry as a field of study owes much to the fact that gold was a valuable commodity throughout our history. In both the ancient Egyptian society and during the Roman Empire. The gold mines were the property of the state, not an individual or group. So there were few days for most people to legally get any gold for themselves. The Alchemists were a varied group scholars and charlatans who aimed to solve this problem by creating the Philosopher’s Stone. Three major streams of alchemy are known, Chinese, Indian, and European, with all three streams having some factors in common. Techniques developed in the European stream ultimately influenced the development of the science of chemistry.
Although alchemists were never successful in changing lead into gold, they made several contributions to modern-day chemistry. Strong acids and bases were discovered, including nitric acid (H2NO3), sulfuric acid (H3SO4), and hydrochloric acid (HCl), and sodium hydroxide (NaOH). Glassware for running chemical reactions were developed, as well as methods for distillation, crystallization, sublimation. Alchemy helped improve the study of metallurgy and the extraction of metals from ores. More systematic approaches to research were developed that allowed the discovery of atoms and laid the groundwork for development of the periodic table.
Inorganic compounds have been known and used since antiquity; probably the oldest is the deep blue pigment called Prussian blue (KFe2(CN)6). However, the chemical nature of these substances was unknown until the late nineteenth and early twentieth century when the modern field of Coordination Chemistry emerged. Much of what we know about inorganic chemistry is based largely on the work of and debates between of Alfred Werner (1866–1919; Nobel Prize in Chemistry in 1913) and Sophus Mads Jorgensen (1837 –1914). After Werner succeeded in these debates, the field of Inorganic Chemistry declined in popularity until the mid-twentieth century when the second world war stimulated renewed interest. During the post-war era, several important discoveries and theories were developed. For example, important theories of bonding in coordination compounds were developed.
Soon after World War II, Crystal Field Theory (CFT) and Ligand Field Theory (LFT) were developed. These are two critical and complimentary theories that provide explanation of spectroscopic, chemical, and structural properties of inorganic coordination compounds; CFT being more simple, and LFT more accurate. In the 1950’s, organometallic catalysts were discovered that catalyzed important organic reactions and the Haber-Bosch Process was discovered. The Haber-Bosch Process is catalyzed by an inorganic oxide catalyst and is one of the world’s most important industrial reactions. It provides for the synthesis of ammonia directly from elemental nitrogen, N2, and hydrogen, H2.
Since its development in the early twentieth century, it has led to the production of an enormous quantity of fertilizer, vastly increasing global food production. As a result, it is estimated that a significant fraction of the nitrogen content in the typical human body is ultimately derived from this process. Yet while the reaction must be run at high temperatures and pressures in the industrial setting, the nitrogenase enzyme on the roots of plants can carry out this reaction at the mild conditions within soil. Intense investigations were then aimed to improve inorganic catalysts through understanding the metal cofactors in enzymes. The link between the Haber-Bosche industrial process and the nitrogenase enzyme was an early bridge between the fields of organometallic chemistry and biochemistry.
Applications of Inorganic Chemistry
Inorganic compounds are used as catalysts, pigments, coatings, surfactants, medicines, fuels, and more. They often have high melting points and specific high or low electrical conductivity properties, which make them useful for specific purposes. For example :
- Ammonia is a nitrogen source in fertilizer. It is one of the major inorganic chemicals used in the production of nylons, fibers, plastics, polyurethanes, hydrazine (used in jet and rocket fuels), and explosives.
- Chlorine is used in the manufacture of polyvinyl chloride (used for pipes, clothing, furniture etc.), agrochemicals (e.g., fertilizer, insecticide, or soil treatment), pharmaceuticals, and chemicals for water treatment and sterilization.
- Titanium dioxide is the naturally occurring oxide of titanium, which is used as a white powder pigment in paints, coatings, plastics, paper, inks, fibers, food, and cosmetics. it also has good ultraviolet light resistance properties, and there is a growing demand for its use in photocatalysts.
- “Application of inorganic chemistry for non-cancer therapeutics”, in which we seek to showcase the many ways in which principles of inorganic chemistry can be applied to tackle challenges in human health and disease. Recent themed issues of Dalton Transactions have explicitly covered metal anticancer compounds (2009) and radiopharmaceuticals (2011), so our intent here is to emphasize other arenas where the creativity of inorganic chemists can contribute to the development of novel therapeutic agents.
- Inorganic Chemistry is not an isolated branch of chemistry. This core science is fully integrated with other areas of chemistry such as organic, physical and analytical chemistry. It deals with the chemistry of all non-organic compounds, and mainly involves the chemistry of metals and especially transition metals. These elements play a crucial role in industrial catalytic processes that are required to produce substances and new materials at a rate far exceeding that of natural chemical reactions. Such catalytic processes can take place in solution (homogeneous catalysis) or on the surface of solid materials (heterogeneous catalysis) and usually involve transition metal elements .However, such elements also play a crucial role in biological processes (so-called bioinorganic chemistry) where metallo-enzymes can activate small molecules like O2, H2O2, NO, H2, CO and CO2, which then act as oxygen transfer reagents, participate in hydration processes, function as messenger molecules or form essential components of redox biology. Furthermore, on the basis of such catalytic reactivity, many metallo-drugs have been developed for the treatment of cancer, arthritis, multiple sclerosis and other autoimmune diseases.
- A huge challenge to inorganic chemists is the drive to optimize existing and develop new technology that will improve the performance of catalysts to save energy and aim for sustainable developments. In this respect, the clarification of the underlying reaction mechanisms in order to understand the underlying chemical processes, whether of industrial, environmental or biological significance, is of utmost importance to the whole world in order to tackle threatening climate changes and severe pollution in densely populated cities. Here inorganic chemistry can indeed have an impact on the quality of life and the wellbeing of the increasing population of the world.
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