4.1 - The Development of the Periodic Table of Elements

Historical Development

Scientist	Contribution and limitation
Antoine Lavoisier	Classified substances as gases, non-metals, metals and metal oxides. The classification was inaccurate because light, heat and some compounds were treated as elements, while some elements in one group had different chemical properties.
Johann W. Dobereiner	Grouped three elements with similar chemical properties into a triad. The atomic mass of the middle element was close to the average atomic masses of the other two; examples include Ca–Sr–Ba and Cl–Br–I. The system applied to only a few elements.
John Newlands	Arranged elements in increasing atomic mass, with seven elements in each row. Similar chemical and physical properties recurred at every eighth element, giving the Law of Octaves. It fitted only the first 17 elements but revealed periodicity.
Lothar Meyer	Plotted atomic volume against atomic mass. Elements at equivalent positions on the curve had similar chemical properties; alkali metals appeared at the peaks. This confirmed the recurrence of element properties.
Dmitri Mendeleev	Arranged elements by increasing atomic mass and placed chemically similar elements in the same vertical column. He left gaps and predicted properties of undiscovered elements from the elements above and below the gap.
Henry Moseley	Related X-ray frequency to proton number, established a unique proton number for each element and arranged elements in increasing proton number. He left gaps and predicted technetium, Tc; promethium, Pm; hafnium, Hf; and rhenium, Re.

Basic Principle of the Modern Arrangement

Elements are arranged in ascending proton number, from 1 to 118.
Elements with similar chemical properties occupy the same vertical column.
Nihonium, Nh; moscovium, Mc; tennessine, Ts; and oganesson, Og were added to Period 7.
Newly discovered elements may be named after a place or a scientist.