What is Chemistry? - Definition, History & Topics

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  • 0:01 Chemistry
  • 0:47 Main Branches
  • 2:53 A Brief History
  • 4:44 Lesson Summary
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Lesson Transcript
Mary Ellen Ellis
Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Chemistry is the science of matter. This may sound simple, but chemistry is a complex and broad topic that broaches a wide variety of fields. From the core of the earth to the farthest reaches of the universe, chemistry is everything and everywhere.

Chemistry: A Definition

Chemistry is the study of matter, including its composition, properties, and structure; how it changes; and how it interacts with energy. This is a pretty simple definition that sums up what is actually a complex and fascinating subject. If you have ever asked why or how something is in the natural world, odds are good that your question and the answer were related to chemistry.

For instance, why is the sky blue? Colors depend on the chemical makeup of substances and what kind of light they reflect. How does an insect walk across the surface of a pond without falling through? The unique properties of water give it a high surface tension, which means that small objects can rest on it without sinking. Chemistry is all around, and anything related to matter involves chemistry.

Main Branches of Chemistry

Organic and Inorganic

Since chemistry is such a broad and vast subject, we can divide it up into more manageable topics to help us more accurately. For example, organic and inorganic chemistry divide up all matter into two categories of study. Organic chemistry is the study of the carbon compounds that make up living things. Inorganic chemistry is the study of everything else.


Biochemistry is the study of the chemical processes that go on in living things and includes the large biological molecules, like DNA, proteins, carbohydrates, and lipids.

Analytical Chemistry

Analytical chemistry is the analysis of chemicals, their properties, and how they react. It also involves the development of tools and methods for doing this analytical work. Analytical chemistry is used by chemists of all disciplines, but some professionals focus solely on the development of analytical methods.

Physical Chemistry

Physical chemistry is the study of physical principles that underlie atoms and compounds, in other words, the physics of chemical compounds. This means that physical chemists examine how particles move, how energy is involved in reactions, the speed at which reactions occur, and how light and energy interact with matter.

Organic, inorganic, analytical, and physical chemistry, along with biochemistry, represent the main topics of study by chemists. There's plenty of overlap. For instance, an organic chemist might be interested in the rate of a reaction of an organic compound, which involves physical chemistry. Or, an inorganic chemist may need an analytical method to investigate the crystal structure of an inorganic compound.

In addition to the main categories of chemistry, there are countless subcategories and specializations that can be named. For example, environmental chemistry is the study of chemical processes in the environment. An environmental chemist might study pollutants in the atmosphere. A geochemist studies the composition and chemical processes of the earth, rocks, and soil, and might work for a petrochemical company. A medicinal chemist studies drugs and how they work to treat diseases. They often work for pharmaceutical companies.

A Brief History of Chemistry

We have established that chemistry is a broad and fascinating topic, but how did it all start? Chemistry, it turns out, is very old. You've probably heard of periods of human history described as the Iron Age or Bronze Age. These are the times when humans started to work with metals. To do so, they had to figure out how to extract metals from the earth and how to melt and mix them in ratios that would give them good materials for making weapons and other tools. This was chemistry in action, and it happened thousands of years ago in prehistoric times.

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Additional Activities

Everyday Chemistry

In this activity, students will be researching examples of chemistry in their everyday life. During this activity, students will classify common chemical reactions as one of the four types, physical, biochemistry, organic, and inorganic chemistry. For example, students might choose the reaction of gasoline in a car engine as an example of organic chemistry, since gasoline is a carbon-based molecule. Or, they might choose the metabolic pathway of cellular respiration as an example of biochemistry. To support their research, students can use online academic sources such as those from scientists or universities.


In this activity, you'll be looking for different examples of each type of chemical reaction described in the lesson: physical, biochemistry, organic, and inorganic chemistry. For each one, describe the reaction that occurs and where you can find it in everyday life. The first one has been done for you as an example. To help you, you can research different types of chemical reactions using academic sources online, such as those from universities, scientists, or news outlets.

Reaction TypeDescription of Example
Physical (Example)Water has molecular interactions with other water molecules that allow water to form ice that is less dense than water, allowing ice to float in my drink
Organic Chemistry
Inorganic Chemistry

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