what do numbers listed on the periodic table represent
The atomic number of an element is the same as the number of electrons or protons in that particular atom. In the periodic table the elements are arranged into periods and groups. A row of elements across the table is called a period. Each period has a number: from 1 to 7. Period 1 has only 2 elements in it: hydrogen and helium. Period 2 and Period 3 both have 8 elements.