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==Introduction== | ==Introduction== | ||
Following the convention of the International Union of Physical and Applied Chemistry (IUPAC), ''''chemical elements'''', in one sense of the term, refers to species, or types, of [[Atom|atoms]].<ref name=iupacdef97>[http://old.iupac.org/goldbook/C01022.pdf chemical element.] Definition of 'chemical element' by the Physical Chemistry Division, unpublished; R.B. 35. IUPAC [International Union of Physical and Applied Chemistry] Compendium of Chemical Terminology 2nd Edition (1997) | Following the convention of the International Union of Physical and Applied Chemistry (IUPAC), ''''chemical elements'''', in one sense of the term, refers to species, or types, of [[Atom|atoms]].<ref name=iupacdef97>[http://old.iupac.org/goldbook/C01022.pdf chemical element.] Definition of 'chemical element' by the Physical Chemistry Division, unpublished; R.B. 35. IUPAC [International Union of Physical and Applied Chemistry] Compendium of Chemical Terminology 2nd Edition (1997) | ||
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Some of the 94 elements , such as the gas [[neon]], are very rare on Earth. Some elements are stable, and will live as long as the universe, while some, known as the ''[[radioactivity|radioactive]] elements'', have finite life times and decay into other elements while emitting [[radiation]]. For example, [[plutonium]] is a well-known radioactive element. | Some of the 94 elements , such as the gas [[neon]], are very rare on Earth. Some elements are stable, and will live as long as the universe, while some, known as the ''[[radioactivity|radioactive]] elements'', have finite life times and decay into other elements while emitting [[radiation]]. For example, [[plutonium]] is a well-known radioactive element. | ||
Revision as of 12:27, 21 July 2009
Introduction
Following the convention of the International Union of Physical and Applied Chemistry (IUPAC), 'chemical elements', in one sense of the term, refers to species, or types, of atoms.[1] Familiar species of atoms include oxygen, copper, gold, and mercury — among the 94 naturally occurring species of atoms on Earth. See tables below. The distinguishing characteristic of a species of atoms is the number of protons in the nucleus of its atoms, referred to as the atomic number, Z, unique for each species of atom and for each corresponding chemical element.
In another sense of the term,'chemical elements' refers to chemical 'substances', specifically to 'pure substances', which in the case of chemical elements each is composed of a population of atoms solely of a single species, or type, of atoms, again as distinguished by its atomic number, Z.[1] In this sense of a 'chemical element', sometimes the term 'elementary substance' is used, but most often 'chemical element' is used for both senses. Familiar examples of such 'pure' chemical substances are segments of wire made solely of copper atoms, and rolls of aluminum foil made solely of aluminum atoms. This second sense, or concept, renders 'chemical element' a somewhat more tangible particular, defining it in terms of a substance.Cite error: Closing </ref> missing for <ref> tag For another example, the element carbon supplies the backbone of numerous species of essential compounds of all animal and plant life on Earth as well of all the fossil fuels (natural gas, petroleum and coal), which are the remains of plant material that once lived. Some compounds may consist of one element only, for instance a nugget of pure gold is made up solely of gold atoms arranged in crystalline form. Very often gold is not pure but an alloy — a mixture — of the elements copper, silver, and gold. Oxygen gas consists of entities [see molecule] each having two oxygen atoms chemically bonded to each other, hence the gas consists of the element oxygen only.
Some of the 94 elements , such as the gas neon, are very rare on Earth. Some elements are stable, and will live as long as the universe, while some, known as the radioactive elements, have finite life times and decay into other elements while emitting radiation. For example, plutonium is a well-known radioactive element.
- ↑ 1.0 1.1 chemical element. Definition of 'chemical element' by the Physical Chemistry Division, unpublished; R.B. 35. IUPAC [International Union of Physical and Applied Chemistry] Compendium of Chemical Terminology 2nd Edition (1997)
- 1. A species of atoms; all atoms with the same number of protons in the atomic nucleus.
- 2. A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. Sometimes this concept is called the elementary substance as distinct from the chemical element as defined under 1, but mostly the term chemical element is used for both concepts.