1. Elements are substances that cannot be decomposed or broken into more elementary substances by ordinary chemical means. Elements were at one time believed to be the fundamental substances but are now known to consist of a number of different elementary particles. More than 100 chemical elements are known to exist in the universe, although several of these, the so -called transuranium elements, have not been found in nature, and can only be produced artificially.
2. Sulfur in its natural form is a tasteless, odorless, light-yellow solid, once forcefully fed to children in the belief that it was good for their health. Sulfur compounds, found in dairy products and eggs, are an essential dietary ingredient. However, hydrogen sulfide, a compound that is very similar to water and smells like rotting eggs, is quite poisonous.
3. The atomic number indicates the number of protons in an atomic nucleus, and is the number assigned to an element in the periodic table. With one proton, the atomic number of hydrogen is 1; ununhexium, an element that has not been found in nature but can be produced in the laboratory, contains 116 protons in its nucleus, and thus has an atomic number of 116.
4. People once used hydrogen gas to lift zeppelins and other airships into the sky, allowing trans-Atlantic voyages by air. However, because the gas is so flammable, it contributed to many explosive accidents, including the Hindenberg explosion in 1937. Airships now use helium gas because it is nonflammable and therefore a safer lifting gas.
5. Buckminsterfullerium is not an element (note, however, that buckminsterfullerene, named for scientist Buckminster Fuller, is a natural physical form of the element carbon). Einsteinium, Berkelium, and Californium are all artificially created radioactive elements discovered in the late 1940s and early 1950s.
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7. Oxygen composes 21 percent by volume or 23.15 percent by weight of the atmosphere; 85.8 percent by weight of the oceans (88.8 percent of pure water is oxygen); and as a constituent of most rocks and minerals, 46.7 percent by weight of the solid crust of the earth. Oxygen comprises 60 percent of the human body.
8. According the United States Mint’s Web site, the alloy in pennies ‘remained 95 percent copper and 5 percent zinc until 1982, when the composition was changed to 97.5 percent zinc and 2.5 percent copper (copper-plated zinc). Cents of both compositions appeared in that year.
9. For many years chemists believed that these gases, because their outermost shells were completely filled with electrons, were inert–that is, that they would not enter into chemical combinations with other elements or compounds. This is now known not to be true, at least for the four heaviest inert gases–argon, krypton, xenon, and radon.
10. Silicon is a semiconductor, in which the resistivity to the flow of electricity at room temperature is in the range between that of metals and that of insulators. The conductivity of silicon can be controlled by adding small amounts of impurities, called dopants. The ability to control the electrical properties of silicon, and its abundance in nature, have made possible the development and widespread application of transistors and integrated circuits used in the electronics industry.