LESSON TWO MATTER
The earth and everything upon it is composed of matter. Matter occurs in three principle physical states—solids, liquids, and gases. Examples of solids are rocks, wood, ice. Examples of liquids are water, gasoline, alcohol. Examples of gases are air, illuminating gas, water vapor or steam.
Molecules. The smallest particle of any pure substance, such as water, iron or salt, which can exist without that substance changing its physical properties, is called a molecule. Thus, water is made up of millions of water molecules, each of which is, so far as we know, exactly like every other water molecule. These molecules are much too small to be seen by even the most powerful microscope. There are ways of measuring them quite accurately, however, as to weight and size. Physical St
Change of Physical State. Matter can be changed from one physical state to another. Thus, by the application of heat, water can be changed from its solid state, ice, to its liquid state, water; and by further heating, to its gaseous state, water vapor. In a similar manner air, which is normally gaseous, by cooling and compression, can be converted into liquid air, and this by still further cooling, can be frozen solid.
Elements. There are compound substances and simple substances, or elements. Common salt, a compound substance, for instance, can be separated by electrical means into two substances—the metal element, sodium; and the poisonous gas element, chlorine. Water, in like manner, can be resolved into two constituent gases, the elements oxygen and hydrogen. Marble, similarly, can be divided into the elements carbon, calcium, and oxygen. All of those last named substances are characterized by the fact they cannot be further subdivided. They are called chemical elements. Chemical elements are the building materials of which everything else on earth is composed.
There are only 92 chemical elements. Several of these are relatively common in everyday life. Among the better known elements are iron, aluminum, copper, tin, lead, zinc, silver, gold, platinum, oxygen, carbon, sulphur, hydrogen, nitrogen, chlorine, iodine and nickel. Some of the elements are exceedingly rare, and have been obtained only in extremely minute traces. Other elements are very common.
Estimates based upon the averaging of thousands of chemical analysis show the upper 10 miles of the earth’s crust to be composed of the following elements in approximately the percentages given.
CHEMICAL COMPOSITION OF THE OUTER 10 MILES OF THE EARTH:*
|ELEMENT||% BY WEIGHT|
|All Remaining 80 elements||0.71|
|TOTAL 92 ELEMENTS||100.00|
* Clarke, The Data of Geochemistry
The striking thing about this table is that by far the greater part of the materials comprising the surface of the earth is composed of only five or six chemical elements. Most of the familiar metals that are used daily occur in amounts of less than one-tenth of one percent of the surface rocks of the earth.
Atoms. The smallest particle of a chemical element is called an atom.
Chemical Compounds. A chemical compound is a substance of definite chemical composition, which is composed of two or more elements. Over 750,000 different chemical compounds are known. Examples of chemical compounds are water (oxygen and hydrogen, abbreviated H2O), salt (sodium and chlorine, abbreviated NaCl), and sugar (carbon, hydrogen and oxygen, abbreviated C12H22O11).
Mixtures. Most substances are not simple chemical compounds, but are rather mixtures or aggregates of various compounds. Wood, for instance, is composed of carbon, hydrogen, oxygen, and a small amount of mineral matter. Wood, however, has not a definite chemical composition, and is not a single chemical compound. Likewise the air is a mixture chiefly of two gases, oxygen and nitrogen.
Chemical Changes. A chemical change involves a change of chemical composition. The grinding of wood into sawdust is a mechanical change which does not affect the chemical composition of the wood; burning of wood, however, is a chemical change. The burning of wood consists in combining the oxygen from the air with substances composing the wood. Without the added oxygen, wood will not burn. After the wood is burned, if all the gases given off are collected and analyzed, it is found that they consist of carbon dioxide and water vapor. A slight residue of mineral matter in the form of ash remains.
Hence, wood + oxygen → water + carbon dioxide + ash.
In a similar manner the burning of gasoline in an automobile results in water vapor and carbon dioxide. This can be seen by watching the steam issue from the exhaust pipes on a cold day.
gasoline + oxygen → water vapor + carbon dioxide
When chemical elements combine in such a manner as to form more complex substances from simple ones the process is called combination. The reverse process of breaking more complex substances down to form simpler ones is called decomposition.
Example of combination:
4Fe + 3O2 → 2Fe2O2
Example of decomposition:
2H2O → 2H2 + O2
Indestructibility of Matter. In all chemical changes of whatever sort it has been found that if all the materials are carefully weighed both before and after the change, while allowing nothing to escape in the meantime, the weight of the materials taking part in the change before the reaction will be exactly equal to the weight of the products resulting from the reaction. This is true not only for the whole, but is also true for each individual element.
All events on the face of the earth involve in one way or another the movement or change in the relative configuration of matter. The rains and the flow of water, the winds, the growth of plants and animals, as well as the operation of automobiles and factories are part of the movement of matter. Matter moves from one place to another, from one physical state to another, or from one chemical combination to another, but in all these processes the individual atoms are not destroyed; they are merely being continuously reshuffled.
- An Introduction to Chemistry, Timm.
- The Spirit of Chemistry, Findlay.
- Matter and Motion, Maxwell.
- The Data of Geochemistry, Clarke.
- Theoretical Chemistry, Nernst.