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John Newlands
The English chemist, John Newlands classified the established elements into various groups proposing the Law of Octaves, made up of elements of increasing atomic mass, where certain properties were repeated every 8 elements. -
Lothar Meyer
Lothar Meyer, químico alemán, publicó su tabla propia periódica con los elementos ordenados de menor a mayor masa atómica. -
Dimitri Mendeleev
The Russian chemist Dimitri Mendeleev published his first periodic table of the elements organized in increasing order of atomic mass. Mendeleev organized his table in horizontal rows leaving empty spaces where they had to incorporate some elements that had not yet been discovered. -
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Dimitri Mendeleev
Mendeleev visualized an apparent pattern: elements with similar chemical properties appear at regular (or periodic) intervals in the vertical columns of the table. The support for Mendeleev's predictions comes after the discovery of gallium (Ga), scandium (Sc) and germanium (Ge) between 1874 and 1885, locating them in those empty spaces, which gave even more value and acceptance of his Periodic Table in the scientific community. -
Henry Moseley
Henry Moseley, through X-ray studies, determined the nuclear charge (atomic number) of the elements, regrouping them in increasing order of atomic number, as we know it today. -
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Johan Dobereiner
The German chemist Johan Dobereiner classified some elements into groups of three called triads, since they had similar chemical properties. For example, in the triad chlorine (Cl), bromine (Br), and iodine (I), you noticed that the atomic mass of Br was very close to the average mass of Cl and I. Unfortunately, not all the elements were grouped into triads and his efforts failed to propose a classification of the elements.