An Elementary Study of Chemistry by William McPherson (best english books to read for beginners .txt) 📕

Compounds. The compounds of gold, though numerous and varied in character, are of comparatively little importance and need not be described in detail. The element forms two series of salts in which it acts as a metal: in the aurous series the gold is univalent, the chloride having the formula AuCl; in the auric series it is trivalent, auric chloride having the formula AuCl3. Gold also acts as an acid-forming element, forming such compounds as potassium aurate (KAuO2). Its compounds are very easily decomposed, however, metallic gold separating from them.

1. From the method of preparation of platinum, what metal is likely to be alloyed with it?

2. The "platinum chloride" of the laboratory is made by dissolving platinum in aqua regia. What is the compound?

3. How would you expect potassium aurate and platinate to be formed? What precautions would this suggest in the use of platinum vessels?

4. Why must gold ores be roasted in the chlorination process?

Division of chemistry into organic and inorganic. Chemistry is usually divided into two great divisions,—organic and inorganic. The original significance of these terms was entirely different from the meaning which they have at the present time.

1. Original significance. The division into organic and inorganic was originally made because it was believed that those substances which constitute the essential parts of living organisms were built up under the influence of the life force of the organism. Such substances, therefore, should be regarded as different from those compounds prepared in the laboratory or formed from the inorganic or mineral constituents of the earth. In accordance with this view organic chemistry included those substances formed by living organisms. Inorganic chemistry, on the other hand, included all substances formed from the mineral portions of the earth.

In 1828 the German chemist Wöhler prepared urea, a typical organic compound, from inorganic materials. The synthesis of other so-called organic compounds followed, and at present it is known that the same chemical laws apply to all substances whether formed in the living organism or prepared in the laboratory from inorganic constituents. The terms "organic" and "inorganic" have therefore lost their original significance.

2. Present significance. The great majority of the compounds found in living organisms contain carbon, and the term "organic chemistry," as used at present, includes not only these compounds but all compounds of carbon. Organic chemistry has become, therefore, the chemistry of the compounds of carbon, all other substances being treated under the head of inorganic chemistry. This separation of the compounds of carbon into a group by themselves is made almost necessary by their great number, over one hundred thousand having been recorded. For convenience some of the simpler carbon compounds, such as the oxides and the carbonates, are usually discussed in inorganic chemistry.

The grouping of compounds in classes. The study of organic chemistry is much simplified by the fact that the large number of bodies included in this field may be grouped in classes of similar compounds. It thus becomes possible to study the properties of each class as a whole, in much the same way as we study a group of elements. The most important of these classes are the hydrocarbons, the alcohols, the aldehydes, the acids, the ethereal salts, the ethers, the ketones, the organic bases, and the carbohydrates. A few members of each of these classes will now be discussed briefly.

Carbon and hydrogen combine to form a large number of compounds. These compounds are known collectively as the hydrocarbons. They may be divided into a number of groups or series, each being named from its first member. Some of the groups are as follows: