Elements - Real-life applications
T HE P ERIODIC T ABLE
Note that an ion is never formed by a change in the number of protons: that number, as noted earlier, is a defining characteristic of an element. If all we know about a particular atom is that it has one proton, we can be certain that it is an atom of hydrogen. Likewise, if an atom has 79 protons, it is gold.
Knowing these quantities is not a matter of memorization: rather, one can learn this and much more by consulting the periodic table of elements. The periodic table is a chart, present in virtually every chemistry classroom in the world, showing the elements arranged in order of atomic number. Elements are represented by boxes containing the atomic number, element symbol, and average atomic mass, in atomic mass units, for that particular element. Vertical columns within the periodic table indicate groups or "families" of elements with similar chemical characteristics.
These groups include alkali metals, alkaline earth metals, halogens, and noble gases. In the middle of the periodic table is a wide range of vertical columns representing the transition metals, and at the bottom of the table, separated from it, are two other rows for the lanthanides and actinides.
A N O VERVIEW OF THE E LEMENTS
As of 2001, there 112 elements, of which 88 occur naturally on Earth. (Some sources show 92 naturally occurring elements; however, a few of the elements with atomic numbers below 92 have not actually been found in nature.) The others were created synthetically, usually in a laboratory, and because these are highly radioactive, they exist only for fractions of a second. The number of elements thus continues to grow, but these "new" elements have little to do with the daily lives of ordinary people. Indeed, this is true even for some of the naturally occurring elements: few people who are not chemically trained, for instance, are able to identify thulium, which has an atomic number of 69.
Though an element can theoretically exist as a gas, liquid, or a solid, in fact the vast majority of elements are solids. Only 11 elements—the six noble gases, along with hydrogen, nitrogen, oxygen, fluorine, and chlorine—exist in the gaseous state at a normal temperature of about 77°F (25°C). Just two are liquids at normal temperature: mercury, a metal, and the non-metal bromine. (The metal gallium becomes liquid at just 85.6°F, or 29.76°C.) The rest are all solids.
The noble gases are monatomic, meaning that they exist purely as single atoms. So too are the "noble metals," such as gold, silver, and platinum. "Noble" in this context means "set apart": noble gases and noble metals are known for their tendency not to react to, and hence not to bond with, other elements. On the other hand, a number of other elements are described as diatomic, meaning that two atoms join to form a molecule.
N AMES OF THE E LEMENTS
ELEMENT SYMBOL.
As noted above, the periodic table includes the element symbol or chemical symbol—a one-or two-letter abbreviation for the name of the element. Many of these are simple one-letter designations: O for oxygen, or C for carbon. Others are two-letter abbreviations, such as Ne for neon or Si for silicon. Note that the first letter is always capitalized, and the second is always lowercase.
In many cases, the two-letter symbols indicate the first and second letters of the element's name, but this is far from universal. Cadmium, for example, is abbreviated Cd, while platinum is Pt. In other cases, the symbol seems to have nothing to do with the element name as it is normally used: for instance, Au for gold or Fe for iron.
Many of the one-letter symbols indicate elements discovered early in history. For instance, carbon is represented by C, and later "C" elements took two-letter designations: Ce for cerium, Cr for chromium, and so on. But many of those elements with apparently strange symbols were among the first discovered, and this is precisely why the symbols make little sense to a person who does not recognize the historical origins of the name.
HISTORICAL BACKGROUND ON SOME ELEMENT NAMES.
For many years, Latin was the language of communication between scientists from different nations; hence the use of Latin names such as aurum ("shining dawn") for gold, or ferrum, the Latin word for iron. Likewise, lead (Pb) and sodium (Na) are designated by their Latin names, plumbum and natrium, respectively.
Some chemical elements are named for Greek or German words describing properties of the element—for example, bromine (Br), which comes from a Greek word meaning "stench." The name of cobalt comes from a German term meaning "underground gnome," because miners considered the metal a troublemaker. The names of several elements with high atomic numbers reflect the places where they were originally discovered or created: francium, germanium, americium, californium.
Americium and californium, with atomic numbers of 95 and 98 respectively, are among those elements that do not occur naturally, but were created artificially. The same is true of several elements named after scientists—among them einsteinium, after Albert Einstein (1879-1955), and nobelium after Alfred Nobel (1833-1896), the Swedish inventor of dynamite who established the Nobel Prize.
A BUNDANCE OF E LEMENTS
IN THE UNIVERSE.
The first two elements on the periodic table, hydrogen and helium, represent 99.9% of the matter in the entire universe. This may seem astounding, but Earth is a tiny dot within the vastness of space, and hydrogen and helium are the principal elements in stars.
All elements, except for those created artificially, exist both on Earth and throughout the universe. Yet the distribution of elements on Earth is very, very different from that in other places—as well it should be, given the fact that Earth is the only planet known to support life. Hydrogen, for instance, constitutes only about 0.87%, by mass, of the elements found in the planet's crust, waters, and atmosphere. As for helium, it is not even among the 18 most abundant elements on Earth.
ON EARTH.
That great element essential to animal life, oxygen, is by far the most plentiful on Earth, representing nearly half—49.2%—of the total mass of atoms found on this planet. (Here the term "mass" refers to the known elemental mass of the planet's atmosphere, waters, and crust; below the crust, scientists can only speculate, though it is likely that much of Earth's interior consists of iron.) Together with silicon (25.7%), oxygen accounts for almost exactly three-quarters of the elemental mass of Earth. Add in aluminum (7.5%), iron (4.71%), calcium (3.39%), sodium (2.63%), potassium (2.4%), and magnesium (1.93%), and these eight elements make up about 97.46% of Earth's material.
In addition to hydrogen, whose distribution is given above, nine other elements account for a total of 2% of Earth's composition: titanium (0.58%), chlorine (0.19%), phosphorus (0.11%), manganese (0.09%), carbon (0.08%), sulfur (0.06%), barium (0.04%), nitrogen (0.03%), and fluorine (0.03%). The remaining 0.49% is made up of various elements.
E LEMENTS I N THE H UMAN B ODY
Fans of science-fiction are familiar with the phrase "carbon-based life form," which is used, for instance, by aliens in sci-fi movies to describe humans. In fact, the term is a virtual redundancy on Earth, since all living things contain carbon.
Essential though it is to life, carbon as a component of the human body takes second place to oxygen, which is an even larger proportion of the body's mass—65.0%—than it is of the Earth. Carbon accounts for 18%, and hydrogen for 10%, meaning that these three elements make up 93% of the body's mass. Most of the remainder is taken up by 10 other elements: nitrogen (3%), calcium (1.4%), phosphorus (1.0%), magnesium (0.50%), potassium (0.34%), sulfur (0.26%), sodium (0.14%), chlorine (0.14%), iron (0.004%), and zinc (0.003%).
TRACE ELEMENTS.
As small as the amount of zinc is in the human body, there are still other elements found in even smaller quantities. These are known as trace elements, because only traces of them are present in the body. Yet they are essential to human well-being: without enough iodine, for instance, a person can develop a goiter, a large swelling in the neck area. Chromium helps the body metabolize sugars, which is why people concerned with losing weight and/or toning their bodies through exercise may take a chromium supplement.
Even arsenic, lethal in large quantities, is a trace element in the human body, and medicines for treating illnesses such as the infection known as "sleeping sickness" contain tiny amounts of arsenic. Other trace elements include cobalt, copper, fluorine, manganese, molybdenum, nickel, selenium, silicon, and vanadium.
MAINTAINING AND IMPROVING HEALTH.
Though these elements are present in trace quantities within the human body, that does not mean that exposure to large amounts of them is healthy. Arsenic, of course, is a good example; so too is aluminum. Aluminum is present in unexpected places: in baked goods, for instance, where a compound containing aluminum (baking powder) is sometimes used in the leavening process; or even in cheeses, as an aid to melting when heated. The relatively high concentrations of aluminum in these products, as well as fluorine in drinking water, has raised concerns among some scientists.
Generally speaking, an element is healthy for the human body in proportion to its presence in the body. With trace elements and others that are found in smaller quantities, however, it is sometimes possible and even advisable to increase the presence of those elements by taking dietary supplements. Hence a typical multivitamin contains calcium, iron, iodine, magnesium, zinc, selenium, copper, chromium, manganese, molybdenum, boron, and vanadium.
For most of these, recommended daily allowances (RDA) have been established by the federal government. Usually, people do not take sodium as a supplement, though—Americans already get more than their RDA of sodium through salt, which is overly abundant in the American diet.
WHERE TO LEARN MORE
Challoner, Jack. The Visual Dictionary of Chemistry. New York: DK Publishing, 1996.
"Classification of Elements and Compounds" (Web site). <http://dl.clackamas.cc.or.us/ch104-04/classifi.htm> (May 14, 2001).
"Elements and Compounds" (Web site). <http://wine1.sb.fsu.edu/chm1045/notes/Intro/Elements/Intro02 htm> (May 14, 2001).
"Elements, Compounds, and Mixtures." Purdue University Department of Chemistry. (Web site). <http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch2/mix html> (May 14, 2001).
"Elements, Compounds, and Mixtures" (Web site). <http://www.juniorcert.net/serve/cont.php3?pg=SC2CEC0339� e; (May 14, 2001).
Knapp, Brian J. Elements. Illustrated by David Woodroffe and David Hardy. Danbury, CT: Grolier Educational, 1996.
"Matter—Elements, Compounds, and Mixtures" (Web site). <http://chem.sci.gu.edu.au/help_desk/Matter.htm> (May 14, 2001).
Oxlade, Chris. Elements and Compounds. Chicago, IL: Heinemann Library, 2001.
Stwertka, Albert. A Guide to the Elements. New York: Oxford University Press, 1998.
Zumdahl, Steven S. Introductory Chemistry: A Foundation, 4th ed. Boston: Houghton Mifflin, 2000.