Periodic table. Computer artwork entitled ^IChemical Galaxy II^i of a periodic table of the elements arranged around a spiral galaxy. Each circle contains an element's chemical symbol and atomic number (the number of protons in the nucleus). Elements with similar chemistry occur in the same spoke and some of the different groups are colour coded (such as the halogens, red). Here, the the normal eight groups are the upper right half of this display, and the lanthanoids, actinoids and transition metals are the lower left half of the display.