![]() ![]() Amedeo Avogadro (1776-1856) in 1821 had proposed that since two volumes of hydrogen gas unite with one volume of oxygen gas, then water is composed of two atoms of hydrogen and one atom of oxygen. ![]() In a previous chapter, we described how John Dalton, the founder of atomic theory, stated that the formula of water was HO, and that consequently the respective atomic weights of hydrogen and oxygen were 1 and 8. Frequently the true atomic weight of an element was not certain, but instead could be a multiple or fraction of the apparent equivalent weight. Unfortunately, even though Berzelius had made very precise measurements, the valence of the elements was not well understood. These arithmetic comparisons depended upon the accurate atomic weights determined by Berzelius ( discussed in a previous chapter). For example, for the alkaline earths, the atomic weight of strontium (42.5) was the arithmetic mean of calcium (20) and barium (65). Johan Wolfgang Döbereiner (1780-1849) in 1829 of the University of Jena (the same university where Karl Marx studied) noticed that there were several “triads” of chemically similar elements in which the middle element had an atomic weight half-way between those of the other two elements. However, scientists are forever searching for fundamental order and patterns, and as additional elements were discovered, trends were observed. Lavoisier’s list was composed of a medley of “simple substances” (as he called them) which he organized into four categories: basic elements (gases), metals, nonmetals, and earths. In 1789 Lavoisier turned the concept of “element” on its head when he proposed that water was a compound and that hydrogen, oxygen, carbon, sulfur, iron, copper, and 25 other substances were the true elements. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |