A compound is a substance that can be decomposed into other different substances; and if the decomposition goes far enough, these substances will be elements.
A mixture is made up of two or more components (elements and compounds or both), physically put together. It differs from a compound whose compounds are chemically united.
(2) Laws.—Law of Definite Proportions: All specimens of a compound contain the same elements in the same proportions.
Law of Multiple Proportions: When two compounds consist of the same elements, the proportion of one is a simple multiple of the proportion of the other.
Law of Combining Proportions: Each element enters into all its compounds by a fixed proportional weight.
The fundamental laws of chemistry are proved by experiment.
(3) The Atomic Theory.—The atomic theory teaches that matter is composed of minute particles which themselves cannot be divided, but which unite to form molecules which can be divided.
A molecule, then, is the smallest amount of a substance that can exist in a free state.
The diameters of molecules have been ascertained by Jeans to be—
| Hydrogen | 20.3 |
| Nitrogen | 29.1 |
| Oxygen | 27.3 |