Last time we talked about the history of the periodic table and some of the reasons behind why it “works”. We also took a look at the first three periods (rows), the very short first period, with only two elements, and the two short periods with eight elements each in them. We also grouped these elements into families (columns) that show similar chemical properties.
Now we shall look at Periods 4 and 5, the two long periods. These periods (and later ones) contain the transition metals. In the first three periods, chemical properties change radically from one element to the next as atomic number increases. For example, fluorine, the most chemically reactive element sits next to neon, which forms no known ground state chemical compounds.