Long before the existence of atoms was established, ancient people recognized that matter was composed of elementary substances, or elements. Elements such as copper, iron, silver, lead, gold, sulfur, carbon, and mercury were the first to be identified, since examples of these could be found in nature. Over time, more elements were discovered.
Alchemists, the forerunners of modern chemists, discovered a number of elements by changing natural substances into new substances in their medieval laboratories between 400 and 1700 AD. Alchemists were driven by a quest to find or make the “philosopher’s stone.” This magical object could supposedly be used to change inexpensive metals into gold and to prepare the “elixir of life,” a potion that could make them enlightened and immortal! While they failed to manufacture gold and to prepare the elixir, they succeeded in isolating and identifying the elements phosphorus, arsenic, antimony, and bismuth.
Classifying Elements
More than 100 elements have been identified so far. Each element is characterized by a specific number of protons and electrons making up its atomic structure. Because of that, no two elements have exactly the same structure or the same set of properties. Each element is unique.
Nonetheless, some elements show similarities in their properties. For example, if you examined each element at room temperature, you would observe that some are gases, some are liquids, and others are solids. Some elements conduct electricity while others do not. Some elements conduct heat easily; others conduct heat poorly. Some elements are attracted by magnets; others are not. These are examples of physical properties of the elements.
Scientists use physical properties to sort elements into categories. Most elements fall into the two categories of metals or nonmetals. Metals and nonmetals differ in significant ways. Most metals tend to be solids at room temperature and good conductors of heat and electric current. Metals also tend to have a shiny or lustrous appearance. Metals are usually malleable (can change shape) and ductile (can be drawn into wires). These properties make it possible to turn gold and silver into jewelry, iron into nails and door hinges, and copper into electrical wiring.
Nonmetals tend to lack the shiny, lustrous appearance of metals. At room temperature, some nonmetals are gaseous, others are liquid, and still others are solid. At room temperature, helium in a balloon is a nonmetal gas, bromine is a nonmetal liquid, and carbon in graphite form is a nonmetal solid.
Physical properties of elements are not the only characteristics used to classify elements. Scientists also use chemical properties to group elements together. Chemical properties can be observed if the element undergoes an exchange or a sharing of electrons between atoms. Metals tend to give up electrons while nonmetals tend to gain or share electrons.
A salt is formed when a metal and a nonmetal combine as they exchange electrons. A common salt that people use every day is table salt. Table salt is formed by combining sodium (metal) and chlorine (nonmetal). Another example is road salt used in winter to prevent slippery roadways. A type of salt that can be used on roads is formed by combining calcium (metal) and chlorine (nonmetal).
Figure 16 Two examples of salts are table salt (a) and road salt (b).
Although scientists have found it useful to classify elements into metals and nonmetals, they have also worked to develop more precise ways to organize the elements. Their efforts led to the development of one of the most useful tools for the study of chemistry: the periodic table of elements.
Fill in the blank.
A
is a substance that is composed of a metal and non-metal.
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