seaborg was awarded the nobel prize in chemistry in 1951. his rearrangement is our modern periodic table. what ultimately determines the position of an element in this modern table is the way the electrons are arranged in the energy levels of the atom. as we move through the table and the number of electrons in an atom increases, the energy level diagrams contain more and more levels and sublevels. both the number and types of electron clouds increase in complexity. this is the energy level diagram for hydrogen's one electron in an s-cloud called the 1s. lithium's three electrons are diagramed like this-- two electrons in the 1s cloud. each cloud can contain two electrons. then the third electron is in another cloud, an s-cloud at the second level. let's move forward to sodium and look at an energy diagram for its 11 electrons. its first two electrons are in the cloud at the 1s level. its next two electrons are in an s-cloud at the second level. this is actually only the first of two sublevels at the second level, so it's called the 2s suble