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Any time two atoms join together, they make a molecule. All the stuff around you is made up of molecules. This includes you! You are actually made up of trillions and trillions of different types of molecules.


When atoms of different types of elements join together, they make molecules called compounds. Water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. This is why it's called H2O. Water will always have 2 times the number of hydrogen atoms as oxygen atoms.

Water Molecule showing 1 Oxygen atom and 2 hydrogen atoms

Molecular Formula

There are only just over 100 types of atoms, but there are millions and millions of different types of substances out there. This is because they are all made up of different types of molecules. Molecules are not only made up of different types of atoms but also different ratios. Like in the water example above, a water molecule has 2 hydrogen atoms and 1 oxygen atom. This is written as H2O.

Other examples are carbon dioxide (C02), ammonia (NH3), and sugar or glucose (C6H12O6). Some formulas can get quite long and complex.

Let's look at the molecule for sugar:

C6 - 6 carbon atoms
H12 - 12 hydrogen atoms
O6 - 6 oxygen atom

It takes these specific atoms in these specific numbers to make up a sugar molecule.

3D Molecule


Molecules and compounds are held together by forces called chemical bonds. There are two main types of bonds that hold most compounds together: covalent bonds and ionic bonds. Some compounds can have both types of bonds.

Both main types of bonds involve electrons. Electrons orbit atoms in shells. These shells want to be "full" of electrons. When they aren't full, they will try to bond with other atoms to get the right amount of electrons to fill their shells.

Covalent Bonds - Covalent bonds share electrons between atoms. This happens when it works out for atoms to share their electrons in order to fill their outer shells.

Ionic Bonds - Ionic bonds form when one electron is donated to another. This happens when one atom gives up an electron to another in order to form a balance and, therefore, a molecule or compound.

Fun Facts about Molecules
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More Chemistry Subjects

Solids, Liquids, Gases
Melting and Boiling
Chemical Bonding
Chemical Reactions
Radioactivity and Radiation
Mixtures and Compounds
Naming Compounds
Separating Mixtures
Acids and Bases
Salts and Soaps
Glossary and Terms
Chemistry Lab Equipment
Organic Chemistry
Famous Chemists

Elements and the Periodic Table
Periodic Table

Science >> Chemistry for Kids

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