Mendeleev-1869

In 1869 Mendeleev arranged the elements into 7 groups with similar properties. He then discovered that the properties of the elements were constant to their atomic weights. So he organized the elements according to their Atomic Mass. This became known as the Periodic Law. He was the first one to make the original Periodic Table. He saw similarities in the elements that others didn't see. He also predicted the mass and make up of elements that hadn't been discovered yet.