107 Stories About Chemistry |
What was the first chemical compound deliberately produced by man? The history of science can give no definite answer to this question. Let us take the liberty to make our own assumptions on this point. The first substance which man prepared, knowing 'beforehand what he wanted to obtain, was a compound of two metals, copper and tin. We have deliberately avoided using the word "chemical, " because the compound of copper and tin (commonly known as bronze) is an unusual one. It is called an alloy. The ancients first learned to smelt metals from their ores and only afterwards to fuse them with each other. Thus, at the dawn of civilization appeared the first seeds of a branch of the future science of chemistry, now called metal chemistry. The structure of compounds of metals and nonmetals usually depends on the valence of the elements contained in them. For example, the molecule of common salt contains positively univalent sodium and negatively univalent chlorine. In the ammonia molecule NH3 negatively trivalent nitrogen is linked with, three positively univalent hydrogen atoms. The chemical compounds of metals with one another (called intermetallic compounds) usually do not obey the laws of valence, and their composition bears no relation to the valence of the reacting elements. For this reason the formulas of intermetallic compounds look rather strange, for instance, MgZn5, KCd7, NaZn12, etc. The same pair of metals can often give several intermetallic compounds; for instance, sodium and tin form nine different combinations.
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