Chemistry is the study of matter and the changes it undergoes, with the atom being its basic functional unit.
Concept #1: Understanding Matter
Matter is anything that takes up space and has mass.
Concept #2: Classifications of Matter
Under appropriate conditions of pressure and temperature, most substances can exist in 3 states of matter.
Concept #3: Volume, compressibility and viscosity of phases of matter
The closeness of molecules within the three phases of matter affects how they respond to changes in volume, pressure and temperature.