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Chemistry: Definition, Types, Branches


Chemistry: Definition, Types, Branches

What Chemistry Is

Chemistry is the science of atoms and molecules the “stuff ” of which everything on Earth and in the universe is made. At the microscopic level a scale of matter too small to be visible to the naked eye chemists study the structures of atoms, the shapes of molecules, and the forces that hold atoms and molecules together. At the macroscopic level a scale of matter that is visible to the naked eye chemists study the chemical and physical properties of the states of matter solid, liquid, gas, or mixture.


But chemistry is not only about matter that is just sitting there. Just as importantly, if not more so, chemistry is also the science of changes, or transformations, of matter. At a nuclear level—a scale smaller than an atom itself—these changes may be the transmutation of one element into another element. At the level of whole atoms and molecules, these changes involve the processes of breaking chemical bonds and forming new bonds with the result that one set of chemical substances—or mixtures of substances—are transformed into a new set of substances that may have properties that differ completely from those of the original materials.


Finally, chemistry is not limited only to substances that exist naturally on Earth. Literally millions of new substances have been synthesized in chemical laboratories that may mimic substances found in nature, although many times these substances may have completely novel chemical and physical properties not found in nature.


Chemists are not finished making new substances. Thousands of new materials are developed every year in laboratories in countries all over the globe. Some of these new substances may lead to cures for debilitative diseases. Some substances might lead to more environmentally sustainable agricultural chemicals or to lightweight, durable structural materials. Others may result in revolutionary new forms of energy. Unfortunately, some may also become agents of war and terrorism—agents of biological and chemical warfare, novel weapon delivery systems, or explosives that can bypass even the most sophisticated high- technology security systems. Scientists never know what applications may be found for their discoveries, or what uses—for good or for evil—others will find for their discoveries.



Chemistry: The Central Science

Chemists often like to call chemistry the central science because chemistry is fundamental to so many other endeavors—biology, medicine, agriculture, physics, astronomy, planetary science, cosmology, geology, and engineering, just to name a few. To say that chemistry is the science of atoms and molecules is really to say that chemistry is the science of everything, since all matter is composed of atoms and molecules.


Examples span all sorts of substances from raindrops, dew, and mist to puddles, ponds, lakes, and oceans; from sand and gravel to rocks, boulders, and mountains; from cotton, wool, and silk to nylon, rayon, and polyester; from natural wood products to plastics, concrete, and steel; from all matter on Earth to all matter on the Moon and other planets, the Sun and other stars, and even to the space between stars and galaxies.


It is difficult to think of anything that is not chemistry. The standard exceptions are usually at the extremes of the very, very small or the very, very large. On the smallest scales of matter, chemistry usually stops at the level of the protons, neutrons, and electrons that make up atoms. It is left to elementary particle physicists to investigate the properties of matter at smaller scales than that—the quarks of which protons and neutrons are made, or other subatomic particles with exotic names like muons, pions, or mesons.


While chemists investigate the nuclear reactions that take place in stars like our Sun and the chemical composition of stars and the space between stars, it is astrophysicists and cosmologists who are concerned about the large scale structures of the universe—galaxies and clusters of galaxies and how they come into being and evolve over time.



Chemistry: The Basis of a Global Industry

The millions of chemical substances—natural or artificial—that have ever been cataloged have had profound effects on the human race. Cave men and women did not know it, but their discovery of how to cook foods, especially meat, altered forever the development of modern humans. Cooking is a chemical reaction that makes food easier to chew and swallow, more digestible, and freer of harmful pathogens, all of which contributed to improved human health, increased life spans, and accelerated brain development.


Substituting metal implements for stone was chemistry. Cave men and women lived in the Stone Age, when rocks were either used as they were found or fashioned or sharpened into weapons, tools, and utensils. The Bronze Age replaced the Stone Age when more modern humans learned to work with copper. Without knowing it, these people were early metallurgists, and metallurgy is chemistry. Soon, the Bronze Age was superseded by the Iron Age, as iron replaced copper in many aspects of life.


In the eighteenth century, the industrial revolution could not have taken place without chemistry. The industrial revolution was built on the steam engine, and steam engines required energy—energy obtained from fuels through chemical processes known as combustion



Today, the chemical industry is a global industry with significant investments in many diverse fields:


1.      Fossil fuels, from coal and petroleum to natural gas

2.     Alternative energy technologies, from nuclear and solar power to ethanol and hydrogen

3.     Pharmaceuticals, everything from analgesics as ordinary as aspirin to blockbuster drugs that fight heart disease and cancer

4.     Cosmetics, from lipstick to perfume

5.     Agricultural products, from fertilizers and pesticides to genetically modified cereal crops

6.     Synthetic materials, from plastics and fibers to rubber

7.      Basic chemicals, everything from household cleaners and wastewater treatment to the pages of this book


So what is chemistry? Everything is chemistry!



What Chemists Do

Chemistry is what chemists do. The field of chemistry encompasses a vast range of activities. Because there is so much demand for the skills of chemists in industry, government, and education, the American Chemical Society is the largest professional scientific organization devoted to a single science, with sister organizations in other countries. Chemists literally are everywhere, and many of them work in laboratories. Chemists may be researchers, teachers, consultants, sales representatives, or technicians. Chemists may hold managerial or administrative positions.


Chemists do all kinds of interesting work. They may be analyzing moon rocks and meteorites, developing lifesaving antibiotics, synthesizing new elements, studying the chemistry of the human body, or probing into theories about the origin of life. Let’s take a

look at some of the subdisciplines of chemistry in which chemists engage.



Analytical Chemists

From the earliest years of alchemy, there has been a demand for people who can answer two questions:


·       What is the composition of a substance?

·       How much of one substance is present in a mixture of substances?


The first question belongs to the domain of qualitative analysis, which examines materials to find out what elements or compounds are in them. The second question belongs to the domain of quantitative analysis, which measures how much of each element or compound is present in a mixture of substances.


Qualitative analysis requires that mixtures be separated into their components, which can be compounds or simple elements. Compounds, in turn, may be further separated into their constituent elements. In geology and the mining industry, for example, rocks, minerals, or soils are analyzed to find out what metals (such as copper, nickel, or titanium) or other elements (such as chlorine or phosphorus) are present.


Municipal water facilities have to identify and remove any contaminants (such as arsenic, lead, or nitrates) that might be present in surface or groundwater supplies before the water enters a city’s water supply system. The food industry analyzes its products so that the labels can inform consumers of what kinds of fats, proteins, carbohydrates, vitamins, minerals, and fiber are present in canned, packaged, and prepared foods. The pharmaceutical industry analyzes samples of all of its products in the attempt to ensure against contamination.


Historically, quantitative analysis involved “wet” chemical techniques—titration, filtration, and gravimetric analysis, for example. Today, most quantitative analyses are done using

instrumental” techniques. An example you might be familiar with is the smog check many municipalities require motor vehicles to pass before they can be registered. In a smog check, a hose connects the tailpipe of a vehicle to a machine that can separate the exhaust gases into different categories—carbon monoxide (CO), oxides of nitrogen (NOx), and unburned hydrocarbons (HC)—and measure the concentration of each gas in parts per million (ppm).


It makes sense that quantitative measurements follow qualitative analyses. In the example of rocks and minerals, once the metal content of ores has been established, then samples of ores can be assayed to find out what percentage of the ore is a metal of value. In the food industry example, labels on food products tell not just what is present in the foods, but how many grams or milligrams of fat, protein, carbohydrates, vitamins, minerals, and fiber are present per serving.



Organic Chemists

Organic chemistry is all about carbon and its compounds. The term organic chemistry originated during the nineteenth century, when chemists thought that carbon-containing substances could only be made by or in living organisms. That definition is no longer in use.


Today we simply define an organic compound as any chemical compound that contains at least carbon and hydrogen. The reason for including hydrogen is to rule out carbon monoxide (CO) and carbon dioxide (CO2), both of which contain carbon but are usually classified as inorganic substances. In addition to carbon and hydrogen, organic compounds may also contain oxygen, nitrogen, phosphorus, sulfur, and other elements.


Much of the modern chemical industry is based on organic chemistry. Petroleum, natural gas, lubricating oils, alcohols, ethers, solvents, weak acids, vitamins and other pharmaceutical products, and many synthetic polymers are all organic compounds.




Biochemistry is that branch of organic chemistry that deals with the chemistry of living organisms. Human bodies, as well as all plants and animals, contain large organic molecules essential to the many biological processes that define replication of organisms, growth, and metabolic activities. Important classes of biochemical substances include carbohydrates, lipids, proteins, and nucleic acids (such as DNA). Biochemists have contributed to chemical knowledge by elucidating the pathways by which photosynthesis takes place in green plants and by which respiration takes place in all living organisms. The syntheses of biologically important substances such as vitamins, cortisone, and hormones are often done by biochemists.


Biochemists are often pharmaceutical chemists. They work for companies that do the research necessary to develop and bring new drugs to the marketplace. Some of the major advances that have been made in the battle against disease have been accomplished by biochemists.



Inorganic Chemists

Simply stated, inorganic chemistry deals with the 117 elements in the periodic table other than carbon. The elements in the periodic table are broadly grouped into three classifications: metals, nonmetals, and metalloids (or semimetals). Inorganic chemists describe the physical and chemical properties of the elements themselves, as well as all of the chemical compounds the elements can form, both in nature and in the laboratory.


Metals—especially iron in the form of steel—are the workhorses of much of modern heavy industry. Thus, inorganic chemists work to develop methods for isolating metals from their ores and for finding new and economically useful applications for metals.


Many nonmetals and their compounds find essential uses in modern society. Life could not exist without liquid water. Most living organisms could not exist without oxygen gas.


Chlorine disinfects drinking water supplies. Salt flavors our food. Neon is used in outdoor lighting. Helium gives balloons and blimps their buoyancy, although helium’s cryogenic (low temperature) uses are much more important. Liquid nitrogen is also a cryogenic substance. In its liquid state carbon dioxide is an environmentally friendly solvent. Fertilizers are mostly used to supply nitrogen, phosphorus, potassium, and sulfur to plants in the form of compounds that plants can assimilate. Hydrogen is being investigated as a clean-burning, renewable fuel that could substitute for fossil fuels.


The metalloids silicon and germanium are the building blocks of computer chips and transistors. Many other elements are used in modern electronics and other technologies. Artificial radioactive substances are produced and used in hospitals every day both for medical diagnosis and for medical treatment. In short, unless an element is particularly rare or expensive, just about every element in the periodic table finds some use in our society.



Physical Chemists

Physical chemists apply the methods of physics to an understanding of the variables that affect how chemical reactions occur so that chemists can control the rates at which chemical reactions take place and improve the yield of products. Three of the major subfields of physical chemistry are quantum chemistry, thermodynamics, and chemical kinetics.


In quantum chemical studies, chemists relate the structures of atoms and molecules at the most fundamental microscopic level to the observable properties of elements and compounds at the macroscopic level. Quantum chemists study the nature of chemical bonding, the forces that hold molecules together in the solid and liquid states, and how the shapes of molecules determine the properties of those substances.


Thermodynamics is the study of chemical equilibrium and of the heat effects associated with chemical reactions. Very importantly, thermodynamicists are employed to maximize the yields of synthetic industrial and pharmaceutical chemicals.


Chemical kinetics is the study of the factors that control the rates at which chemical reactions take place. Kineticists investigate the effects of changing pressure, concentration of reactants, and temperature on the rates of chemical reactions. Many reactions take place too slowly for industrial applications at ambient temperatures and pressures, so kineticists find ways to speed up economically useful chemical reactions.


One way to speed up chemical reactions is to employ catalysts, chemical substances that speed up chemical reactions but that remain unchanged by the reactions. The best catalysts in the world are biochemical catalysts—the enzymes found in all living organisms. For many industrial processes, kineticists seek to find catalysts that at least approach the efficiency of naturally occurring enzymes.



Nuclear Chemists

Another branch of physical chemistry is nuclear chemistry. Nuclear chemists work with radioactive materials, which may occur naturally or be produced artificially in nuclear reactors. Nuclear chemists study the properties of these substances and investigate ways in which radioactive materials may be useful in a wide range of applications, including medicine and agriculture among other fields.


For the past three-quarters of a century, nuclear chemists have synthesized a total of 28 elements that do not occur in nature but occupy positions in the periodic table after the element uranium. As of 2012, a total of 118 elements are known. Nuclear chemists continue to work at extending the periodic table to even heavier elements.



Chemical Engineers

Chemical engineers are applied physical chemists. Chemical engineers usually work in industry. Their job is to take benchtop synthetic methods that are usually done on the scale of a few grams of a substance and scale the processes up to producing metric tons of the same substances. The ability to apply the principles of thermodynamics and chemical kinetics to real-life problems of manufacturing useful chemical substances on a large scale is the trademark of a chemical engineer.



Educational Requirements to be a Chemist

Chemists generally have a college degree. Community colleges may offer two-year certification programs to be a laboratory technician. Most four-year colleges and universities offer a bachelor’s degree in chemistry, and some universities may also offer a bachelor’s degree in chemical engineering. Colleges and universities with graduate programs may offer master’s and doctor’s degrees in chemistry. Entry-level positions in research or sales usually require a bachelor’s or master’s degree. To be a leader of a research program usually requires a Ph.D. in chemistry or chemical engineering.


Teaching chemistry at the high school level usually requires a bachelor’s degree in chemistry, or a degree in a related science such as biology or physics with a strong chemistry background. Teaching chemistry at a community college requires a master’s or doctor’s degree in chemistry. Teaching at a four-year college or university almost always requires a Ph.D., especially if there is an expectation that faculty conduct research programs.


Regardless of an undergraduate’s specific plans for a career in chemistry or other related field, the sequence of required college courses is fairly standard:


1.      One year each of general, organic, and physical chemistry

2.     One semester each of analytical chemistry, advanced inorganic chemistry, and electives that might include physical organic chemistry, advanced organic, and inorganic chemistry

3.     Biochemistry, or nuclear chemistry

4.     One to two years of mathematics, including calculus and differential equations

5.     One year of physics

6.     General education courses that include English composition, speech, computer science, the social sciences, and the humanities

7.      Electives that might include additional mathematics or physics, plus biology, geology, or other areas of interest


Laboratory work is a major component of an undergraduate education in chemistry. The courses taken during the first three years usually include laboratory work. In the senior year a student may take advanced laboratory courses or participate in research under the supervision of a faculty member. An undergraduate research experience is especially important for students intending to continue on to graduate programs. It is not unusual for undergraduate students to have already published a paper or two in a refereed research journal before graduating.


Here is some advice to remember if you are a student. You never know where your career path may lead you. A required course today may be the ticket to success on the job at some future date. Get the most you can out of every class you take. Get to know your professors. Believe it or not, they are real people, and you never know when you might want a letter of recommendation from one of them someday! And don’t neglect those general education courses. No matter what you do in life, the ability to communicate—and to communicate well—is essential. Master both oral and written communication skills, and you will find more doors opening to you down the road.



Conclusion: Chemistry as a Human Enterprise

Chemistry does not get done all by itself. People do chemistry. Chemistry, together with all of the other natural sciences, is as much a human enterprise as are the humanities or the social sciences. The next chapter is intended to present chemistry within its historical context, highlighting some of the major figures who have contributed to chemistry over the centuries.


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