Element, Chemical
A chemical element is a fundamental substance of the material world. Each element has an identity; for example, gold consists of only gold atoms, and a gold atoms is unlike any other atom. Indeed, a gold atom can be split, but the particles that (electrons, protons, etc.) that constitute a gold atom are not gold. It could be said that subatomic particle are generic, interchangeable. Atoms, on the other hand, have an identity, and constitute the identity of an element.
Chemists use the concept of atomic number to identify particular elements. Atomic number is the number of protons in an atom's nucleus, which means that atomic number constitutes, so to speak, a particular atom's identity tag. Thus, when we ascertain that a particular atom has 11 protons, we can immediately identify it as a sodium atom. No other atom has 11 protons. Unfortunately, despite their clearly defined identity, chemical elements sometime exhibit puzzling behaviors that have led scientists to question the concept of a distinct chemical element. Namely, a particular element can occur as two or more isotopes. If sodium (atomic number 11) has 11 protons, we assume that the number of neutrons will also be 11, giving us a total of 22, which chemists call atomic mass. Ideally, atomic mass should be the atomic number multiplied by two, but that is not always the case. In fact, beryllium (atomic number 4) usually occurs with a mass number of nine. Isotopes can thus be defined as atoms of the same element showing a discrepancy between atomic number (which never changes) and mass number.
A hydrogen (atomic number 1) atom does not have a neutron, which means that its atomic number and atomic mass are the same. When a neutron is added, hydrogen's atomic mass rises to two, yielding deuterium, in isotope which is necessary for the manufacture of the hydrogen bomb. However, if a proton is added to the hydrogen atom, a new element, helium is created. An additional proton will create lithium (atomic number 3), a metal widely used in industry, and so on.
There are 92 elements occurring in nature, with uranium (atomic number 92) at the end of the sequence which starts with hydrogen. However, since 1940, when Philip Abelson (b. 1913) and Edwin McMillan (1907-1991) created a new element, neptunium (atomic number 93) by bombarding uranium with neutrons, scientist have created a number of artificial elements, some of which are highly unstable, lasting only a fraction of a second. Transuranic (beyond uranium) elements now go up to the atomic number of 118. However, elements 113, 155, and 117 have yet to be created.
At room temperature, most elements appear in solid form; only two are liquids (including mercury, which is a metal), and 11 are gases. In chemistry, each element is known by its symbols: these symbols, usually a letter or two letter, usually represent an element's archaic name (in languages including Greek and Latin). Thus the chemical symbol for iron is Fe, from ferrum, the Latin word for iron. Thus, a chemical symbol often does not represent an element's everyday name, and that can cause some confusion. For example, while Al (aluminum, or aluminium --in Europe) seems straightforward, K (potassium) and Na (sodium) seem somewhat misleading.
Early Greek science postulated the existence of a primordial element as the foundation of the material universe. Thus, for example, Thales (c.624-545 B.C. regarded water as the fundamental element. Empedocles (died c. 430 B.C. identified four basic elements: earth, water, air, and fire. While the quaternary scheme of Empedocles eventually became part of official science thanks to the enormous influence of Aristotle (384-322 B.C., who incorporated the idea of four element into his theory of nature, early alchemists identified particular substances as elements. For example, they were familiar with certain metals, including gold, which inspired mystical reverence as the perfect element. Other elements discussed by both Western and Arabic alchemists are sulphur and mercury, regarded as important spiritual principles. During the Renaissance, Paracelsus (1491-1541) introduced the idea of three primal elements. Expanding on the sulphur-mercury duality in alchemy, Paracelsus created a trinity consisting of salt, representing the body, sulphur, representing the soul, and mercury, representing the spirit. In 1661, Robert Boyle (1627-1691) published The Sceptical Chymist, criticized both the tradition conceptions of elements, including the Aristotelian four element s and the alchemical triad of salt, sulphur, and mercury. In his view, elements were pure substances.
The modern scientific concept of element was not formulated until the late eighteenth century. In 1789, in his influential Elementary Treatise on Chemistry, Antoine-Laurent Lavoisier (1743-1794) defined an element as a substance that cannot be chemically decomposed into a more basic substance. Essentially, Lavoisier's definition is in agreement with contemporary atomic theory. Lavoisier's list of 33 elements include light, heat, certain compounds, but also around 20 substances which he correctly identified as elements: among his elements are oxygen, nitrogen, hydrogen, sulphur, antimony, arsenic, bismuth, cobalt, copper, gold, iron, lead, manganese, mercury, molybdenum, nickel, platinum, silver, tin, tungsten, and zinc. Coincidentally, Lavoisier's book was published in year the French Revolution started. In 1794, Lavoisier was executed as an enemy of the Revolution. Those who pleaded for his life were told that "the Republic has no need for scientists."
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