In nature we have simple and compound bodies. The former are called Elements. We must not confuse these elements with the so-called elements—earth, air, fire, and water. These are really compound bodies. An element is a substance or a gas which is not composed of more than one constituent; it is itself—a compound of perfectly identical particles. Every “compound” body, therefore, must be made up of some of the elements, of which there are sixty-five. These bodies are divided into non-metallic and metallic elements, and all bodies are composed of them, or are these bodies themselves. The list is as follows. The non-metallic elements are “metalloids.” We have omitted fractions from the weights, on which chemists differ.
TABLE OF ELEMENTS WITH THEIR CHEMICAL SYMBOLS AND COMBINING WEIGHTS.
| Name. | Symbols. | Atomic or Combining Weights. | Derivation of Name. | |
|---|---|---|---|---|
| Oxygen | O | 16 | Gr. Oxus, acid; gennaō, to make. | |
| Hydrogen | Gaseous | H | 1 | Gr. Udor, water; gennaō, to make. |
| Nitrogen | N | 14 | Gr. Natron, nitre; gennaō, to make. | |
| Chlorine | Cl | 35 | Gr. Chloros, green. | |
| Iodine | Solid | I | 127 | Gr. Ioeides, violet. |
| Fluorine | F | 19 | Fluor spar, the mineral. | |
| Carbon | C | 12 | Lat. Carbo, coal. | |
| Sulphur | S | 32 | Lat. Sulphurium. | |
| Phosphorus | P | 31 | Gr. Phos, light; pherein, to carry. | |
| Arsenic* | As | 75 | Gr. Arsenicon, potent. | |
| Silicon | Si | 28 | Gr. Silex, flint. | |
| Boron | B | 11 | Gr. Borax, Arab., baraga, to shine. | |
| Selenium | Se | 79 | Gr. Selene, the moon. | |
| Tellurium | Te | 129 | Lat. Tellus, the earth. | |
| Bromine | Fluid | 80 | Gr. Bromos, offensive smell. |
METALS.
The term “combining weight” requires a little explanation. We are aware that water, for instance, is made up of oxygen and hydrogen in certain proportions. This we will prove by-and-by. The proportions are in eighteen grains or parts of water, sixteen parts (by weight) of oxygen, and two parts (by weight) of hydrogen. These are the weights or proportions in which oxygen and hydrogen combine to form water, and such weights are always the same in these proportions. Chemical combination always occurs for certain substances in certain proportions which never vary in those compounds, and if we wish to extract oxygen from an oxide we must take the aggregate amount of the combining weights of the oxide, and we shall find the proportion of oxygen; for the compound always weighs the same as the sum of the elements that compose it. To return to the illustration of water. The molecule of water is made up of one atom of oxygen and two atoms of hydrogen. One atom of the former weighs sixteen times the atom of the latter. The weights given in the foregoing table are atomic weights, and the law of their proportions is called the Atomic Theory.
An atom in chemistry is usually considered the smallest quantity of matter that exists, and is indivisible. A molecule is supposed to contain two or more atoms, and is the smallest portion of a compound body. The standard atom is hydrogen, which is put down as 1, because we find that when one part by weight of hydrogen is put in combination, it must have many more parts by weight of others to form a compound. Two grains of hydrogen, combining with sixteen of oxygen, makes eighteen of water, as we have already seen.
Take an example so plainly given by Professor Roscoe, remembering that the numbers in our table represent the fixed weight or proportion by weight in which the simple body combines. The red oxide of mercury contains sixteen parts by weight of oxygen to two hundred parts by weight of mercury (we see the same numbers in the table); these combined make two hundred and sixteen parts of oxide. So to obtain 16 lbs. of oxygen we must get 216 lbs. of the powder. It is the same all through, and it will be found by experiment that if any more parts than these fixed proportions be taken to form a compound, some of that element used in excess will remain free. Lime is made up of calcium and oxygen. We find calcium combining weight is forty, oxygen sixteen. Lime is oxide of calcium in these proportions (by weight).
When we wish to express the number of atoms in a compound we write the number underneath when more than one; thus water is H2O. Sulphuric acid H2SO4. As we proceed we will give the various formulæ when considering the chief elements.
In chemistry we have acids, alkalis, and salts, with metallic oxides, termed bases, or bodies, that when combined with acids form salts. Alkalis are bases.