Group 1 is the first vertical group on the periodic table. It is also called the alkali metals and it includes lithium, sodium, potassium, rubidium, and cesium. As you travel down the group from top to bottom, the atomic radii of the elements increase. That is to say that the distance from the center of the atom (the nucleus) to the outermost electron orbital increases. This is due to the fact that the number of electrons in each element increases as you travel down the group. The more electron energy shells there are, the further away from the center the outermost electrons will be for any given element.