what are the columns on a periodic table called?
The atomic number is the number of protons each atom has in its nucleus. By arranging the elements in this way, those with similar properties (characteristics) are grouped together. As with any grid, the periodic table has rows running left to right, and columns running up and down. The rows are called PERIODS and the columns are called GROUPS. Hydrogen (H) is the first element in the periodic table because it has just one proton in its nucleus. Helium (He) is second, because it has two protons, and so on.