Elements - Chemistry

Literally millions of substances have so far been either discovered or synthesized and formally identified. Are these the fundamental building blocks of matter? Happily not, for their classification alone would pose an insurmountable task. In fact, all these substances are merely combinations of much smaller numbers of building blocks called elements. Elements are substances that cannot be decomposed into two or more simpler substances by ordinary physical or chemical means. The word ordinary excludes the processes of radioactive decay, whether natural or artificial, and high-energy nuclear reactions that do transform one element into another. When a substance contains two or more chemical elements, we call it a compound. For example, hydrogen and oxygen are elements because no further chemical separation is possible, whereas water is a compound because it can be separated into hydrogen and oxygen by passing an electric current through it.

Binary compounds are substances, such as water, that contain two elements, ternary compounds contain three elements, and quaternary compounds contain four elements, and so on. At present, scientists have identified some 112 chemical elements. A few have been known since before recorded history, principally because they occur in nature as elements rather than in combination with one another in compounds. Gold, silver, lead, copper, and sulfur are chief among them. Gold is found in streams in the form of little granules (placer gold) or nuggets in loosely consolidated rock. Sulfur is associated with volcanoes, and copper often can be found in its native state in shallow mines. Iron occurs in its elemental state only rarely (in meteorites); it usually is combined with oxygen or other elements. In the second millennium B.C., ancient metallurgists somehow learned to reduce iron oxide to iron with charcoal in forced-draft fires, and the Iron Age was born.

The names of the chemical elements and the symbols that designate them have a fascinating history. Many elements have Latin roots that describe physical or chemical properties, such as gold (aurum, symbol Au), copper (cuprum, Cu), iron (ferrum, Fe), and mercury (hydrargyrum, Hg). Hydrogen (H) means "water former." Potassium (kalium, K) takes its common name from potash (potassium carbonate), a useful chemical obtained in early times by leaching the ashes of wood fires with water. Many elements take their names from Greek and Roman mythology: cerium (Ce) from Ceres, goddess of plenty; tantalum (Ta) from Tantalus, who was condemned in the afterlife to an eternity of hunger and thirst while close to water and fruit that were always tantalizingly just out of reach; and niobium (Nb) from Niobe, daughter of Tantalus. Some elements are named for continents: europium (Eu) and americium (Am). Other elements are named after countries: germanium (Ge), francium (Fr), and polonium (Po). Cities provide the names of other elements: holmium (Stockholm, Ho), ytterbium (Ytterby, Yb), and berkelium (Berkeley, Bk). Still more elements are named for the planets: uranium (U), plutonium (Pu), and neptunium (Np). Other elements take their names from colors: praseodymium (green, Pr), rubidium (red, Rb), and cesium (sky blue, Cs). Still others honor great scientists: curium (Marie Curie, Cm), mendelevium (Dmitri Mendeleev, Md), fermium (Enrico Fermi, Fm), einsteinium (Albert Einstein, Es), and seaborgium (Glenn Seaborg, Sg).