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Chemical Compounds

by Ron Kurtus ( 2007)

A compound is a molecule consisting of two or more elements. It is different than a mixture of different elements or materials. Molecules that are the combination of atoms of the same element are not considered compounds. Compounds are classified according the the number of different elements in the molecule.

Questions you may have include:

• How are compounds different than mixtures?
• What molecules are not compounds?
• How are compounds classified?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Compound different than a mixture

Compounds are the chemical bonding of two or more different elements into a molecule. They are different than mixtures, which is a combination of two or more different materials that are not in chemical combination. Mixtures can be separated by mechanical means, while compounds can't be separated that way.

Another way a compound is different than a mixture is that an individual compound has the same proportion of each element in all of its molecules. For example, the water molecule H₂O is a compound that always is made up of two atoms of hydrogen and one atom of oxygen.

Examples of other compounds include:

Carbon monoxide: CO

Carbon dioxide: CO₂

Acetone: (CH₃)₂CO

Zinc sulfide: ZnS

Magnesium chloride: MgCl₂

Molecules that are not compounds

There are a number of molecules that are a combination of the same element. Although they can be involved in chemical reactions, they are not considered compounds. Common examples of such molecules include:

Oxygen molecule: O₂

Ozone: O₃

Hydrogen molecule: H₂

Nitrogen molecule: N₂

Chlorine molecule: Cl₂

Types of compounds

Compounds can be classified according to the number of different elements in its molecule. The most common are the binary compound, which consists of two elements, and the ternary compound, consisting of three elements.

Binary compounds have two elements

Examples of binary compounds include:

Table salt or sodium chloride: NaCl

Iron sulfide: FeS

Water: H₂O

Ternary compounds have three elements

Examples of ternary compounds include:

Sodium hydroxide: NaOH

Perchloric acid: HClO₄

Sulfuric acid: H₂SO₄

Summary

A compound consists of two or more elements in a chemically combined as a molecule. This is as opposed to a mixture, which is not a chemical combination. There are molecules that are not considered compounds. Compounds are classified according the the number of different elements in the molecule.

Answers to Readers' Questions

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Mini-quiz to check your understanding

1. Since sand is silicon dioxide (SiO₂), is it a compound or a mixture?

2. Is neon (Ne) gas a compound?

3. Is clay (HAlSiO₄) a binary or ternary compound?

If you got all three correct, you are on your way to becoming a Champion in Chemistry. If you had problems, you had better look over the material again.

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