The Periodic Table
Chemists classify elements according to their position in the periodic table.
Periodicity is the term used to describe the repeating pattern of properties observed within the periodic table.
Elements that have similar chemical properties are grouped in columns called groups (or families).
For example, alkali metals (the first column of elements) and noble gases (the last column of elements).
Metals are to the left of the heavy, stepped line in the 2nd picture, while nonmetals (except for hydrogen) are clustered to the right of the line.
Semimetals (or metalloids) are the elements with properties intermediate between those of metals and nonmetals and appear adjacent to the bold line.