The periodic table is a chart which organizes the chemical elements. The elements are categorized according to the following attributes: 

Atomic Number - number of protons in the nucleus

Atomic Mass - sum of the number of protons plus neutrons in the nucleus

Group - columns or multiple columns in the periodic table. Elements in a group share similar chemical and physical properties.

Period - rows from left to right in the period table. Elements in a period have the same number of energy shells.

Matter can exist in the form of a pure element, but combinations of elements are more common.

Molecule - a molecule is a combination of two or more atoms (could be from the same or different elements, such as H₂ or H₂O)

Compound - a compound is a combination of two or more chemically-bonded elements. Generally, compounds are considered to be a subclass of molecules (some people will argue they are determined by the types of chemical bonds).