Chemical symbol: Difference between revisions
imported>Peter Schmitt (removing some duplicate information) |
imported>Peter Schmitt (Ions and isotopes added) |
||
Line 12: | Line 12: | ||
However, in a few cases there is no relation between the English word and its symbol. | However, in a few cases there is no relation between the English word and its symbol. | ||
For instance, Fe (derived from Latin "ferrum") is the symbol for [[iron]]. | For instance, Fe (derived from Latin "ferrum") is the symbol for [[iron]]. | ||
== Ions == | |||
An [[Ion]] of an element is indicated by a superscript, where + and - stand for positive and negative charge, respectively. | |||
For example, H<sup>+</sup> means a hydrogen ion, and Ca<sup>2+</sup> a calcium ion (with two electrons missing). | |||
<br> | |||
The ion H<sup>+</sup> of hydrogen is a [[proton]] | |||
which — in atomic reactions — is also indicated as p. | |||
== Isotopes == | |||
In atom physics, [[isotope]]s of an element are distinguished | |||
by adding the [[atomic mass]] as a superscript (usually, but not always, attached to the left of the symbol). | |||
<br> | |||
The isotopes of hydrogen have symbols of their own: | |||
<sup>1</sup>H is hydrogen H, <sup>2</sup>H is [[deuterium]] D, and <sup>3</sup>H is [[tritium]] T. | |||
== Examples == | |||
A simple example for a chemical reaction formula is | A simple example for a chemical reaction formula is |
Revision as of 11:43, 6 December 2009
Chemical symbols are the international standard way to denote chemical elements. In particular, they are used in chemical formulas to describe the composition and structure of molecules, and in reaction formulas. A chemical symbol consists of one or two letters — the initial letter of its scientific name in uppercase which, in most cases, is followed by a suitable lowercase letter from the name. (Sometimes, on a temporary basis, for new artificial elements initially 3-letter symbols may be used.)
Well-known examples of one-letter symbols are H for hydrogen and O for oxygen, Ca is the two-letter symbol for calcium. For most elements the symbol fits its English name because this name is also derived from the scientific name (which usually is of Greek or Latin origin). However, in a few cases there is no relation between the English word and its symbol. For instance, Fe (derived from Latin "ferrum") is the symbol for iron.
Ions
An Ion of an element is indicated by a superscript, where + and - stand for positive and negative charge, respectively.
For example, H+ means a hydrogen ion, and Ca2+ a calcium ion (with two electrons missing).
The ion H+ of hydrogen is a proton
which — in atomic reactions — is also indicated as p.
Isotopes
In atom physics, isotopes of an element are distinguished
by adding the atomic mass as a superscript (usually, but not always, attached to the left of the symbol).
The isotopes of hydrogen have symbols of their own:
1H is hydrogen H, 2H is deuterium D, and 3H is tritium T.
Examples
A simple example for a chemical reaction formula is
- 2 H2 + O2 → 2 H2O
which states that hydrogen and oxygen can react and produce water.
In China, each chemical element is assigned an ideograph as its symbol; most of them have been explicitly created for this purpose (see Chinese characters for chemical elements).
Chemical symbols may also be changed to show if one particular isotope of an atom that is specified, as well as to show other attributes such as the ionization and oxidation state of a chemical compound.
Attached subscripts or superscripts specifying a nucleotide or molecule have the following meanings and positions:
- The nucleon number (mass number) is shown in the left superscript position (e.g., 14N)
- The number of atoms of a nucleotide is shown in the right subscript position (e.g., N2)
- The proton number (atomic number) may be indicated in the left subscript position (e.g., 64Gd)
- If necessary, a state of ionization or an excited state may be indicated in the right superscript position (e.g., state of ionization Na+)