Elements are listed in order of increasing atomic number, lined up so that elements which exhibit similar properties are arranged in the same row or column as each other. There are 90 elements on the periodic table that occur in nature. All of the other elements are strictly man-made. Technetium was the first element to be made artificially.
The rows of the periodic table are called periods. An element’s period number is the highest unexcited energy level for an electron of that element. Columns of elements help to distinguish groups in the periodic table. Elements within a group share several common properties and often have the same outer electron arrangement.