Chemical elements

In chemistry, an element is a relatively simple manifestation of matter characterized both by exhibiting unique physical and chemical properties and by having an underlying structure consisting entirely of a single species, or type, of atom, of which, naturally occuring on Earth, 94 different species exist, comprising 94 different elements (e.g., hydrogen, helium, copper, uranium). All matter around us (solids, liquids, and gases) are made up of atoms, either of one species of atom (e.g., a nugget of pure gold; molecules of oxygen gas, or dioxygen) or a combination of atoms of different species (e.g., an alloy of copper and tin; sucrose [table sugar) molecules of carbon, hydrogen, and oxygen). Water is a compound of the elements hydrogen and oxygen, and for water the compound is a molecule in which the two constituent atoms form covalent bonds of two hydrogen atoms bonded to an oxygen atom arranged so that each molecule binds with each other weakly through hydrogen bonding. The element carbon is an important part of most living creatures as well as of fossil fuels (e.g., petroleum, coal, natural gas), the remains of plant material that once lived. The atoms comprising other elements are rare on earth, such as the noble gas neon. Some elements consist of stable atoms in that they maintain their uniqueness for lifetimes longer than we can measure, while some elements have finite life times and decay to other elements, while sending out radiation &mdash; the so-called radioactive elements. A well-known radioactive element is plutonium. Chemists have created about 20 non-naturally-occuring elements, characterized by having very short life times and being radioactive. Whereas each element comprises a single species of atom, many species come in varieties, called isotpes, differing among themselves for a given species by the number of neutrons in the nucleus of the atoms.

We recall that an atom consists of a positive nucleus of charge eZ, where e is the elementary charge, and the integral number Z is the atomic number, or number of protons. Remember that Z electrons (of charge &minus;e) "orbit" the nucleus, so that an atom is neutral. The elements are distinguished by their value of Z. For instance, the elements mentioned have the Z-value in brackets: hydrogen(1), oxygen(8), carbon(6), neon(10), plutonium(94). The naturally occurring elements have Z-values from 1 to 94 (with plutonium being extremely rare in nature and mainly man-made). The man-made elements run from Z = 95 to 118. The names of the elements are of historical origin and may vary between languages. The atomic number Z is a unique and universal label of an element, as is its international chemical symbol consisting of one or two letters.

There is a maximum to the number of elements due to the fact that a nucleus contains Z positively charged particles (protons). These repel each other by Coulomb forces and are bound together by strong nuclear forces. At a certain number of protons the strong nuclear forces will lose from the Coulomb forces&mdash;which add up with increasing number of protons &mdash; and the nucleus will no longer be stable. This is likely to happen between Z = 120 and Z = 130.


 * See Atomic electron configuration for the orbital occupancies of atoms in their so-called ground state.

Notes     Ag (silver) is from Argentum    Au (gold) is from Aurum    Cu (copper) is from Cuprum    Fe (iron) is from Ferrum    Hg (mercury) is from Hydrargyrum    K  (potassium) is from Kalium    Na (sodium) is from Natrium    Pb (lead) is from Plumbum    Sb (antimony) is from Stibium    Si (silicon) is from Silicium    Sn (tin) is from Stannum    W  (tungsten) is from Wolfram    Man-made elements Z = 112, ..., 118 are not listed 