4.1.1 History of Development of Periodic Table

Johann Dobereiner – Law of Triads

1. Nature contained triads of elements
2. 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

1. Plotted the atomic volumes of the elements against the atomic weight, and found that the chemical properties of the element recur periodically.
2. Also notice that the elements occupying the corresponding position of the curve show similar chemical properties.

Mendeleev – First Periodic Table

1. 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.
2. left empty space in the periodic table for elements that haven’t been discovery at that time.
3. 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.
4. 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)

1. managed to measure the proton number of atoms.
2. 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.
3. managed to predict the existence of four undiscovered elements from the proton number.