| Of what is matter composed? Suppose you had a bar of pure gold (one should be so fortunate!) and divided it in half, and then the halves in half, and the halves of the half in half, and so on. Would you ever get to the point that if you made one more division you would no longer have gold? The answer is yes, and that point is the atom that indivisible part of matter. An atom is the fundamental unit of matter the smallest particle of an element that can enter into a chemical reaction. As early as 600 to 400 B.C., the Greek philosophers Leucippus, Democritus, and Epicurus were already formulating the concept of an atom, using philosophical logic rather than the experimental methods we now use to investigate the basic structure of matter. As a matter of fact, today we can actually see images of atoms (see Human Endeavors box in this chapter).
| Why did I select a gold bar for my example? Gold is what is called an element a substance made up of only one kind of atom. There are 92 elements that occur naturally on this earth, ranging from hydrogen, which is the smallest, to uranium, which is the largest. In addition to those 92, scientists have successfully produced at least 14 more elements in the laboratory. These 14, of which plutonium is one, do not occur in nature but must be produced under the artificial conditions of the laboratory. The elements that comprise 99 percent of the chemical makeup of living things are carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus. | |
|
|
| | |
|
| In order to make it easier to refer to elements, chemists have developed a shorthand of symbols to represent them. For example, in a chemist's shorthand the elements found most often in living things are represented by capital letters: C (carbon), H (hydrogen), O (oxygen), N (nitrogen), S (sulfur), and P (phosphorus). As you can see, the shorthand is usually based on the first letter (or first two letters) of the name of the element. This isn't always the case, however, since there are so many elements. Therefore, in some instances chemists use the letters of the Latin or Greek name. For example, sodium in Latin is natrium, so the symbol for sodium is Na. When the symbol has two letters, the second letter is always lowercase. |
|
Posting Komentar