and all the elements in group 0 are unreactive non-metals. The zigzag, staircase, line in the diagram of the periodic table above separates the metals, on the left, from non-metals, on the right.

In 1843, Leopold Gmelin worked with the Dobereiner’s system and developed a table of 55 elements that contained many of the similar relationships later found in the modern periodic table. Then in 1857 ...