Johann Dobereiner – Law of Triads
- Nature contained triads of elements
- The middle element had properties that were an average of the other two members when ordered by the atomic weight (the Law of Triads).
John Newlands – Law of Octaves
Any given element will show similar behavior to the eighth element following it in the table.
Lothar Meyer – Meyer’s Curve
- Plotted the atomic volumes of the elements against the atomic weight, and found that the chemical properties of the element recur periodically.
- Also notice that the elements occupying the corresponding position of the curve show similar chemical properties.
Mendeleev – First Periodic Table
- arrange the elements according to the ascending order of atomic mass and put all the elements that have same chemical properties in the same group.
- left empty space in the periodic table for elements that haven’t been discovery at that time.
- Although he arranged the elements in ascending order of the atomic mass, he changed the order if the chemical properties of the element did not match its group.
- From the empty space present in his table, he even predicted the existence and properties of unknown elements which he called eka-aluminum, eka-boron, and eka-silicon.
H.J.G. Moseley – Modernized the Periodic Table by Arranging The Elements According to the Ascending Order of Atomic Number (Proton Number)
- managed to measure the proton number of atoms.
- arranged the elements in the periodic table according to the ascending order of the atomic number (proton number), but not the atomic mass, as done by Mendeleev.
- managed to predict the existence of four undiscovered elements from the proton number.