John Dobereiner was a German scientist who developed the Law of Triads. Each triad was a group of three elements similar to each other; for example, alkali formers were grouped together, and so were salt formers. In 1829, he noticed that bromine, an element that fell about halfway between chlorine and iodine in atomic weight, also seemed halfway between them in its other properties. Other “triads” that he discovered were: calcium, strontium, and barium, and sulfur, selenium, and tellurium. Soon, the lines were blurred, causing confusion, and these triads were treated like coincidences.