Matter is anything that takes up space and has mass. All matter is made up of atoms.

Atoms are the smallest unit of a chemical element. In Greek atom means uncuttable.

Elements are made up of 1 type of atom. There are about 120 elements.
example: hydrogen (H), Oxygen (O), Carbon (C), Nitrogen (N), Iron (Fe), Aluminum (Al), Gold (Au) and Calcium (Ca).

The periodic table organizes all the chemical elements according to their properties.

Molecules are formed when 2 or more of the same or different atoms join together. Examples: water (H2O), salt (NaCi), oxygen (O2), sugar (C6H12O6), carbon dioxide (CO2).

A compound is when 2 or more different atoms join not to be confused with molecules all compounds are molecules, but not all molecules are compounds. Examples: carbon dioxide (CO2), salt (NaCi), hydrogen peroxide (H2O2).
Not examples: O2, H2.

The subscripts tell you how many "atoms" of each element for that molecule. Example: H2= 2 atoms hydrogen, H2O2= 2 atoms hydrogen, 1 atom oxygen.

Coefficients are used to multiply the number of molecules you are making. Example: 2H2O= 4 atoms hydrogen, 2 atoms oxygen.