Reference: Boorse 1966: The World of Atom
PART IV – NEW CONFIRMATION OF CHEMICAL ATOMIC THEORY
THE WORLD OF ATOM by Boorse
Chapter 19: Polyatomic Molecules (Stanislao Cannizzaro 1826 – 1910)
Cannizzaro adopted a molecular, i.e., polyatomic, view of the elements, and showed that the atomic weights of elements, prepared in volatile compounds, could be deduced by the application of Avogadro’s hypothesis together with accurate combining weight data and vapor densities. Cannizzaro’s great contribution was that “the different quantities of the same element contained in different molecules are all whole multiples of one and the same quantity, which always being entire, has the right to be called an atom.”
Chapter 20: The Periodic Table of the Elements (Dmitri Ivanovich Mendeleev 1834 – 1907)
Mendeleev discovered that the properties of the elements are related to their atomic weights in a periodic manner. This not only settled their atomic weights but also predicted previously unknown elements. It also provided the recognition of true relations of different groups of elements to one another, e. g., valency. The elements most widely distributed in nature have small atomic weights, and all such elements are distinguished by their characteristic behavior. They are thus typical, and the lightest element, hydrogen, is therefore rightly chosen as the typical unit of mass.
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MAIN POINTS
- Molecules of elements are polyatomic.
- The different quantities of the same element contained in different molecules are all whole multiples of one and the same quantity.
- This minimum quantity, always being entire, has the right to be called the atomic weight of the element.
- The properties of the elements are related to their atomic weights in a periodic manner.
- Different groups of elements are related in terms of their valences.
- The elements most widely distributed in nature have small atomic weights.
- The lightest element, hydrogen, is rightly chosen as the typical unit of mass.
THEORY
Atoms have atomic weights that are multiples of a basic quantity. The properties of the elements are related to their atomic weights in a periodic manner. Therefore, the atoms have a definite internal structure.
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