The Structure of Matter

Author: J.B. Hoag

Let us examine a piece of metal very carefully. If we polish its surface and look at it under a microscope we shall see small crystals of various shapes. Their shape depends on the heat and mechanical treatment which the metal received. These microscopic crystals are arranged in haphazard fashion and are sometimes long and narrow, sometimes fatter, like distorted polygons. Frequently there are impurities such as slag in the region between the crystals. If, now, any one crystal could be still further magnified, it would be found to contain atoms which are arranged in beautiful geometrical patterns, called space-lattices. This has been revealed to us by means of X-ray studies. The atoms are essentially fixed in position, although they may vibrate a little about their "fixed" positions. In addition to the metals, there are hosts of other physical objects in the world around us. Be they metals or non-metals, they are all but complex forms and combinations of only ninety-two basic substances called elements. Aluminum and copper are elements, whereas brass is an alloy of the elements zinc and copper. Each element is composed of small parts, called atoms, each measuring approximately 0.000,000,01 cm (= 10^-8 cm), or four-billionths of an inch in diameter. In some substances, the atoms form close-knit groups, called molecules. For instance, two hydrogen atoms and one oxygen atom make up a molecule of water.

The atoms are not solid spheres. In fact a great deal is already known about the insides of an atom. There is a heavy central core or nucleus, which is positively charged, around which electrons revolve rapidly, like the planets revolving around the sun. In an ordinary, electrically-neutral atom, the positive charge of the nucleus is equal to the total negative charge of all the planetary electrons around it.

The outermost electrons of an atom determine to a large extent the chemical combinations which are possible, and are called the valence electrons. If these electrons are disturbed and then return to their normal states, light rays are emitted. On the other hand, if electrons close to the nucleus are disturbed, and then return to their normal states, X-rays are emitted. When some of the planetary electrons are removed completely from the atom, it is left with an excess of positive charge and is said to be ionized. Then, it is an ion. Finally, when parts are added to or ejected from the nucleus itself, or when the nucleus is split asunder, a new element is produced. This is "atom smashing".