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Molecules

When you have finished this page, try the Molecules Quiz.

A molecule is the smallest part of a substance called a compound that still is that substance. For example, a molecule of water is the smallest bit of water that still is water. A molecule of a substance cannot be seen by the naked eye - a drop of water is made up of many, many molecules of water.

Molecules are composed of atoms joined together chemically. Molecules do not have an electrical charge.

Scientists believe that molecules are always moving. They can be solids, liquids or gases. Molecules move the most and are the furthest apart when they are gases. Molecules are closest together and move the most slowly when they are solids. Molecules that are liquids movement is between those of gases and those of solids.

A formula tells what elements make up a molecule. For example, a molecule of water is made up of two hydrogen atoms and one oxygen atom. The formula for a molecule of water is H2O.

Molecules come in different sizes and molecular weights. Their atoms can be arranged in different ways. Molecules in substances can be split up in chemical reactions to form other molecules. They can also recombine into larger molecules or be broken down into smaller molecules,

 

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