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Precisely define valence please

  1. Jan 22, 2016 #1
    So I looked up valency on chem wikis, wikipedia and a bunch of textbooks. But everywhere I looked the definitions turned out to be different. The IUPAC defines it as the number of univalent atoms or groups that can combine with or be replaced with one atom of the element under consideration. I find this confusing given that we're using the concept of valency (in the word univalent) in its definition. How is that a legitimate defintion? Can something be defined by itself? I would appreciate a precise and universal defintion of valency. And if it's impossible to define it in that manner, I'd be content with a short analysis of how to describe it conpletely, in a few sentences.
  2. jcsd
  3. Jan 22, 2016 #2
    It's basically the number of bonds an atom can form. But it is a rather rough concept. An atom can make fractional bonds and things like that. But to first approx hydrogen has valence 1, oxygen 2, nitrogen 2, carbon 4, helium zero.
  4. Jan 25, 2016 #3


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    Technical definitions are often an attempt to prescribe a consensus meaning for a term. This contrasts starkly with a dictionary which has the goal of describing meaning. The difference between description and prescription is clear; description describes what is, and prescription defines what should or must be. Valence is not well defined because people use it with different meaning. I suggest you avoid it. There is little likelihood that a single definition/usage will ever be agreed to. I say this because it is used both as a pedagogical tool (teaching the kiddies) and (much more rarely) as a term used to communicate between experts, and since the audiences are different, the meaning will probably remain different as well. Valence is a simple concept which attempts to simplify the quantum mechanics involved in determining (predicting) the structure of a given assembly of atoms by assigning to each atom a property (valence) and ignore all of the other atoms which it may interact with. Three questions you should ask anyone who is teaching you valence: Is it useful for both neutral atoms and atoms in compounds, and metals? Is an atom's valence dependent on temperature? Is an atom's valence dependent on pressure? Is an atom's valence dependent on WHICH atoms are surrounding it? Oh, sorry that's four.
  5. Jan 25, 2016 #4
    So basically it's best to simply resort to a, shall I say, intuitive concept of valence, rather than a definitive statement? You're saying that I simply should adapt to the contextual meanings and stop trying to generalize the term?
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