What is an Element in Chemistry?

Instructor: Marion Carroll

Marion is a 30-year veteran of industry and academia primarily in the fields of biochemistry and genomics.

Sometimes the simplest definitions are the most difficult to articulate. Chemical elements form the foundational components of what creates matter and materials. Here we will describe the principle components of elements, what makes them unique to form the materials of everyday life.

What Is Matter in Chemistry?

To put it shortly: matter is everything! When looking at any form of material, many things stand out, like color, size, form, or even some intellectual or experiential assessment of its use or function. What about when one touches any form of material: what is the experience like? Is it hot or cold, soft or hard, dull or sharp? To understand what an element in chemistry is we first must observe. Is it pure, is it reactive, will it melt or boil, and how long will it last in the environment? These are questions to begin to understand the nature of an element in chemistry.

When we talk about matter, we are referring to things made of either atoms, the smallest complete particle of a chemical element that exist, or molecules, a structure formed from two or more different elemental atoms. Carbon atoms are everywhere, and carbon is one of the first pure elements ever studied. A compound you might know is carbon dioxide, which is a molecule made of two different elemental atoms, one carbon and two oxygen. Matter is truly all around you.

What Makes an Element?

All elements have some of the same structural components. Each atom of an element, no matter which one we want to look at, has three main components: electrons, protons and neutrons. Protons are positive particles and neutrons are neutral particles, though both of them are in the center of the atom, forming the nucleus. Electrons, meanwhile, have a negative charge and are outside the nucleus. All of these particles, the electrons, protons, and neutrons, are collectively called subatomic particles and they determine the size, charge, physical and chemical properties which determine the unique identity all elements we know! Illustrated is a rendering of an atom of carbon and an atom of neon.

Electrons, protons, and neutrons
Electrons, protons, and neutrons

However, it's not enough to know that elements have electrons, protons, and neutrons. For two atoms to be the same element, they must have the same number of protons which will also mean they have the same atomic number. Another key characteristic is atomic weight. Atomic weight is a reflection of the weight of the total number of neutrons and protons of the atom. These values are listed systematically in a table of elements which will be described later.

Let's consider carbon as our example of a typical atom. Carbon is very abundant in nature and its atomic weight was actually the standard for measuring the atomic weight of all other elements. Carbon's atomic number is 6, which means it has 6 protons. It also has 6 electrons and 6 neutrons. Its atomic weight is 12.01.

Organizing Elements

You may be familiar with the infamous organization chart of all known elements: The Periodic Table. It was developed in the 1800s as a result of the discovery that elements differ from one another in very incremental ways. Take a look at this example of the periodic table.

The periodic table of elements.
The periodic table of elements.

This has been marked to show you specifically Hydrogen (H), Carbon (C), Oxygen (O), and Uranium (U). The smallest elements are located in the upper left of the table and get larger as you move down the columns (groups) and left to right along the rows (periods). The smallest known element is Hydrogen. It's hard to say what is the largest element is to be. If speaking of naturally occurring elements most would agree that uranium is the largest with an atomic weight of 238 atomic mass units (atm). Man made elements and other radioactive elements created from uranium can be larger.

Compare the placement of carbon and oxygen. Carbon's atomic number is 6 and its atomic weight is 12.01. Oxygen, on the other hand, has an atomic number of 8 and its atomic weight is 15.99! You can see the effect of the elements' respective subatomic particles and how this affects the placement of each element on the table.

Expression of Elements

Even though atoms of the same element share properties, there are still some interesting differences that can be observed between them. Carbon, which you now know a lot about, usually exists as a solid on earth, and can be mined as black rock (graphite) which is capable of fueling fire and holding heat, but it can also form one of the most precious and hardest elements on earth: diamonds. The same element forms two very different things!

Diamonds and Graphite

Another element, oxygen, is as abundant in nature as carbon and is just as critical to the formation of life. Unlike carbon, its natural form is as a gas on earth. Oxygen tends to form bonds with other chemicals readily, though it exists on its own as part of a 2-atom pair, O-2.

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