Valency: Difference between revisions
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:''This article is about the chemical concept of valence, or valency. Other meanings are at [[valence]].'' |
:''This article is about the chemical concept of valence, or valency. Other meanings are at [[valence]].'' |
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:[[File:Wasser.png|thumb|[[Oxygen]] has twice the valence of [[hydrogen]], |
:[[File:Wasser.png|thumb|[[Oxygen]] has twice the valence of [[hydrogen]], so a molecule of [[Water|H<sub>2</sub>O]] requires twice as many hydrogen atoms as oxygen atoms.]] |
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In [[chemistry]], '''valency''' |
In [[chemistry]], '''valency''' or '''valence''' is the [[number]] of [[chemical bond]]s that an [[atom]] of a certain [[chemical element|element]] can form. |
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For a long time, people thought that this number was a fixed property of the element in question. They thought that [[carbon]] always has four bonds, [[oxygen]] always has two, and [[hydrogen]] always has one. The problem was seen only later. For example, [[phosphorous]] sometimes behaves as if it had three bonds, a valence of three. At other times though, it seems to have five bonds. |
For a long time, people thought that this number was a fixed property of the element in question. They thought that [[carbon]] always has four bonds, [[oxygen]] always has two, and [[hydrogen]] always has one. The problem was seen only later. For example, [[phosphorous]] sometimes behaves as if it had three bonds, a valence of three. At other times, though, it seems to have five bonds. |
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[[IUPAC]] saw this problem, and proposed [[oxidation number]]s. This means there is one number per chemical element. The problem |
[[IUPAC]] saw this problem, and proposed [[oxidation number]]s. This means there is one number per chemical element. The problem with this approach is that it leaves aside most{{Citation needed|date=July 2020|reason=Which ones?}} chemical properties of the elements in question. |
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A '''valence band''' is the highest occupied molecular orbital normally occupied by valence electrons for a given solid at [[absolute zero]] temperature. |
A '''valence band''' is the highest occupied molecular orbital normally occupied by valence electrons for a given solid at [[absolute zero]] temperature. |
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== Other websites == |
== Other websites == |
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*[ |
*[https://web.archive.org/web/20180630000234/iupac.org/goldbook/V06588.pdf "Valence"] from the [[IUPAC]] ''[[Gold Book]]'' (PDF file) |
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[[Category:Chemistry]] |
[[Category:Chemistry]] |
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Revision as of 23:40, 1 July 2020
- This article is about the chemical concept of valence, or valency. Other meanings are at valence.
Oxygen has twice the valence of hydrogen, so a molecule of H2O requires twice as many hydrogen atoms as oxygen atoms.
In chemistry, valency or valence is the number of chemical bonds that an atom of a certain element can form.
For a long time, people thought that this number was a fixed property of the element in question. They thought that carbon always has four bonds, oxygen always has two, and hydrogen always has one. The problem was seen only later. For example, phosphorous sometimes behaves as if it had three bonds, a valence of three. At other times, though, it seems to have five bonds.
IUPAC saw this problem, and proposed oxidation numbers. This means there is one number per chemical element. The problem with this approach is that it leaves aside most[source?] chemical properties of the elements in question.
A valence band is the highest occupied molecular orbital normally occupied by valence electrons for a given solid at absolute zero temperature.
Related pages
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