What two properties are the modern periodic table based on?

The modern periodic table is based upon the atomic number and the physical properties of each element. The periods, or rows, are arranged by increasing atomic number. Each column, or group, of elements has similar physical properties.

Each element in the modern periodic table is represented by its chemical symbol, which has one or two letters. The element's atomic number is displayed above its symbol. The modern periodic table is oftentimes color coded to classify elements as metals, nonmetals or metalloids. Periods in the table progress from metals, on the left, to metalloids, in the center, and then to nonmetals, on the right.