Antoine Lavoisier is believed to be the first scientist who classify elements into a few groups.
He had mistakenly classified light and heat as matter and baryta (barium hydroxide), lime and silica as element
Johann Dobereiner--
Johann Dobereiner noticed that the atomic weight of strontium is equal to the average atomic weight of calcium and barium, and these 3 elements possessing similar chemical properties.
He grouped these 3 elements together and name it as a triad
After this discovery, he proposed that nature contained triads of elements, and named this as the Law of Triads
According to the Law of Triads, the atomic mass of the middle element is equals to the average of the other two members and all 3 elements show similar chemical properties
John Newlands
John Newlands arranged the elements according to the ascending order of their atomic mass, and managed to publish his version of periodic table
He grouped the elements together base on their chemical properties and found that the chemical properties of element changes when the atomic mass increases but similar chemical properties will repeat every 7 elements.
For example, he found that the chemical properties of the 8th element is equals to the 1st element, and the chemical properties of the 9th element is equals to the 2nd
Base on this discovery, he proposed the Law of Octaves
Lothar Meyer
Meyer estimated the volume of atom by using an equation
He plotted the atomic volumes of the elements against the atomic weight, and found that the chemical properties of the element recur periodically
He also notice that the elements occupying the corresponding position of the curve show similar chemical properties
For example, all the elements located at the peak of the graph (Lithium, sodium and potassium)show similar chemical properties
Meyer constructed a periodic table which he gave to a colleague for evaluation. (This may be consider as the first but not published periodic table.)
Mendeleev-
Mendeleev
Mendeleev published his periodic table & law in 1869.
He 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.
He 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
Moseley managed to measure the proton number of atoms.
He then 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.
This correction was considered as a very important step in modernisation of periodic table.
He managed to predict the existence of four undiscovered elements from the proton number.
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