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What Are Elements?

Elements Definition and Introduction


NGC 604, a region of the ionized element hydrogen in the Triangulum Galaxy.

The first element on the periodic table is hydrogen, which is the most abundant element in the universe. Stars and nebulae consist primarily of this element.

Hubble Space Telescope, photo PR96-27B

An element or chemical element is the simplest form of matter in that it cannot be further broken down using any chemical means. Yes, elements are made up of smaller particles, but you can't take an atom of an element and perform any chemical reaction that will break it apart or join its subunits to make a bigger atom of that element.

What Makes It a Different Element?

So, you may be asking yourself what makes one material a different element from another? How can you tell if two chemicals are the same element? Sometimes examples of a pure element look very different from each other. For example, diamond and graphite (pencil lead) are both examples of the element carbon. You wouldn't know it based on appearance or properties. However, atoms of diamond and graphite each share the same number of protons. The number of protons, particles in an atom's nucleus, determines the element. Elements on the periodic table are arranged in order of increasing numbers of protons.

Examples of Elements

The element with one proton is hydrogen. Helium contains two protons and is the second element. Lithium has three protons and is the third element, and so on.

Pure elements contain atoms that all have the same number of protons. If the number of protons is mixed, you have a mixture or a compound. Examples of pure substances that are not elements include water (H2O), carbon dioxide (CO2) and salt (NaCl). See how the chemical composition of these materials includes more than one type of atom? If the atoms had been the same type, the substance would have been an element even though it contained multiple atoms. Oxygen gas, (O2), is an example of an element.

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