The first period of the periodic index comprises just two elements, Hydrogen and Helium, which also happen to be the two simplest elements posessing only a 1s orbital. You would be forgiven for thinking that period one is dull. After all there is only so much you can do with one electron (Hydrogen) and Helium is totally inert with it's highly stable pair of electons. You would, however, be wrong. Helium has some interesting physical properties that set it apart from the other elements and hydrogen makes an excellent study atom due to its simplicty. Without giving further away I'll encourage you to read about the elements of period one.