Molecule

                                Molecule 

molecule is formed when two or more atoms join together through chemical bonds. Think of atoms as individual building blocks, like LEGOs; when you snap two or more of them together, you create a molecule. These atoms can be of the same type, such as two Oxygen atoms joining to form the oxygen gas (O_2) we breathe, or they can be different types, such as two Hydrogen atoms joining one Oxygen atom to create a water molecule (H2O).

The force that holds these atoms together is called a chemical bond, which happens when atoms share or exchange their outer electrons to become more stable. A molecule is the smallest part of a substance that can exist on its own while still keeping all the chemical properties of that substance. For example, if you break a water molecule apart, it is no longer water—it just becomes separate hydrogen and oxygen atoms. Interestingly, molecules often have completely different properties than the atoms they are made of; while oxygen and hydrogen are both gases, they combine to form liquid water!