The organizational characteristics of the periodic table of the elements are within a system where all known elements are classified. They are placed from left to right and top to bottom in increasing order of their atomic numbers. The elements are arranged in seven horizontal rows called periods, and in 18 vertical columns called groups or families. Down and to the left increases the atomic radius and the ionic radius. Upwards and to the right increases ionization energy, electron affinity and electronegativity.
