In the periodic table of (chemistry) elements, there are all sorts of patterns. Metals all cluster together. The noble gases (elements that don't react with much of anything) all live over on the right hand side in one column. Corrosive things like oxygen, chlorine, fluorine, etc. appear vertically above one another. The element right below a given place in the table most often has properties very similar to the one above it (but probably more so). The number of columns in the table has a specific meaning.
Most significantly for chemistry, when the structure of the table was first figured out, it was full of obvious empty slots. Those predicted the existence of previously unknown elements, all of which were subsequently discovered. We are still filling in the bottom row...Element 115 just this week, in fact. Are there more rows in the periodic table? Maybe---if the proposed "island of stability" exists: http://en.wikipedia.org/wiki/Island_of_stability
The original is very useful in chemistry. E.g. going right from carbon, which can make 4 bonds, nitrogen can make 3, oxygen 2, florine 1. Going down from oxygen, sulfur is a heavy oxygen that can make many of the same compounds, with we understand to be different from its weight and greater number of electrons.
