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Elements


Pure Substances

A pure substance is called an element . An element is a pure substance because it cannot be separated into any other substances. Currently, 92 different elements are known to exist in nature, although additional elements have been formed in labs. All matter consists of one or more of these elements. Some elements are very common; others are relatively rare. The most common element in the universe is hydrogen, which is part of Earth’s atmosphere and a component of water. The most common element in Earth’s atmosphere is nitrogen, and the most common element in Earth’s crust is oxygen. Several other elements are described in the musical video at this URL:

http://www.youtube.com/watch?v=d0zION8xjbM (3:47)

Particles of Elements

The smallest particle of an element that still has the properties of that element is the atom . Atoms actually consist of smaller particles, including protons and electrons, but these smaller particles are the same for all elements. All the atoms of an element are like one another, and are different from the atoms of all other elements. For example, the atoms of each element have a unique number of protons.

Consider carbon as an example. Carbon atoms have six protons. They also have six electrons. All carbon atoms are the same whether they are found in a lump of coal or a teaspoon of table sugar ( Figure below ). On the other hand, carbon atoms are different from the atoms of hydrogen, which are also found in coal and sugar. Each hydrogen atom has just one proton and one electron.

Carbon is the main element in coal (left). Carbon is also a major component of sugar (right).

Q: Why do you think coal and sugar are so different from one another when carbon is a major component of each substance?

A: Coal and sugar differ from one another because they contain different proportions of carbon and other elements. For example, coal is about 85 percent carbon, whereas table sugar is about 42 percent carbon. Both coal and sugar also contain the elements hydrogen and oxygen but in different proportions. In addition, coal contains the elements nitrogen and sulfur.

Summary

  • An element is a pure substance that cannot be separated into any other substances. There are 92 naturally occurring elements.
  • Each element has a unique set of properties that is different from the set of properties of any other element.
  • For about 2000 years, people accepted Aristotle’s idea that all matter is made up of just four elements: earth, air, water, and fire. Starting about 500 years ago, scientists began discovering all of the elements that are known today.
  • The smallest particle of an element that still has the properties of that element is the atom. All the atoms of an element are like one another, and are different from the atoms of all other elements.

Vocabulary

  • atom : Smallest particle of an element that still has the element’s properties.
  • element : Pure substance that cannot be separated into any other substances.

Practice

At the following URL, choose any three elements and learn about their properties, history, and uses. Then create a table comparing and contrasting the three elements.

http://www.webelements.com/

Review

  1. What is an element?
  2. Why can an element be identified by its properties?
  3. Explain why the following statement is either true or false: The idea that all matter consists of the elements was first introduced a few hundred years ago.
  4. How are atoms related to elements?

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