The main building blocks in chemistry are chemical elements, which are substances made of a single atom. Each chemical is unique, composed of a set number of protons, neutrons and electrons, and is identified by a name and a chemical symbol, such as "C" for carbon. The elements that scientists have discovered so far are listed in the periodic table of elements, and include both elements that are found in nature like carbon, hydrogen and oxygen, as well as those that are manmade, like Lawrencium. Chemical elements can bond together to form chemical compounds, which are substances made up of multiple elements, like carbon dioxide (which is made of one carbon atom connected to two oxygen atoms), or multiple atoms of a single element, like oxygen gas (which is made of two oxygen atoms connected together). These chemical compounds can then bond with other compounds or elements to form countless other substances and materials.
Analytical chemistry involves the analysis of chemicals, and includes qualitative methods like looking at color changes, as well as quantitative methods like examining the exact wavelength(s) of light that a chemical absorbed to result in that color change.
These methods enable scientists to characterize many different properties of chemicals, and can benefit society in a number of ways. For example, analytical chemistry helps food companies make tastier frozen dinners by detecting how chemicals in food change when they are frozen over time. Analytical chemistry is also used to monitor the health of the environment by measuring chemicals in water or soil, for example.
Biochemistry, as mentioned above, uses chemistry techniques to understand how biological systems work at a chemical level. Thanks to biochemistry, researchers have been able to map out the human genome, understand what different proteins do in the body and develop cures for many diseases.
Related: Unraveling the human genome: 6 molecular milestones
Inorganic chemistry studies the chemical compounds in inorganic, or non-living things such as minerals and metals. Traditionally, inorganic chemistry considers compounds that do not contain carbon (which are covered by organic chemistry), but this definition is not completely accurate, according to the ACS.
Some compounds studied in inorganic chemistry, like "organometallic compounds," contain metals, which are metals that are attached to carbon — the main element that's studied in organic chemistry. As such, compounds such as these are considered part of both fields.
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Inorganic chemistry is used to create a variety of products, including paints, fertilizers and sunscreens.
Organic chemistry deals with chemical compounds that contain carbon, an element considered essential to life. Organic chemists study the composition, structure, properties and reactions of such compounds, which along with carbon, contain other non-carbon elements such as hydrogen, sulfur and silicon. Organic chemistry is used in many applications, as described by the ACS, such as biotechnology, the petroleum industry, pharmaceuticals and plastics.
Physical chemistry uses concepts from physics to understand how chemistry works. For example, figuring out how atoms move and interact with each other, or why some liquids, including water, turn into vapor at high temperatures. Physical chemists try to understand these phenomena at a very small scale — on the level of atoms and molecules — to derive conclusions about how chemical reactions work and what gives specific materials their own unique properties.
