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Properties of elements...

  1. Sep 15, 2016 #1
    We say about an element that this element is solid, liquid and gaseous in nature...(like we say oxygen and nitrogen are gaseous)...My question is that how can we say that an ELEMENT is solid, liquid or gaseous...From what I understand, elements are kind of ''represented'' by their atoms...So how can we tell from individual atoms that that element is solid, liquid or gaseous...For example, Hydrogen is an element..how can we tell from single H atoms that hydrogen is what???...A lot of people have told me that we say that by observing physical properties from H2 molecules, is that true???
  2. jcsd
  3. Sep 15, 2016 #2


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    You sure can not. Phase is a property of a huge number of atoms/molecules.
  4. Sep 16, 2016 #3
    So how can we say about an element that element x is solid, liquid or gaseous at room temperature???
  5. Sep 16, 2016 #4


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    Look at a sample large enough?
  6. Sep 16, 2016 #5
    And is that ''sample'' individual atoms (which is not likely except for nobel gases), the H2 or O2 form or any other form???
  7. Sep 16, 2016 #6


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    Depends on many things, like which allotrope we deal with.

    "Individual atoms" is a rather poor category to think about, we almost never see isolated atoms, unless in very exotic conditions. Chemistry and large part of physics is about relatively large amounts of matter, not single atoms.
  8. Sep 16, 2016 #7


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    Since solid, liquid and gas are descriptions of how atoms and molecules are arranged in bulk matter, it makes no sense to apply the terms to single atoms or even small groups of atoms. But the terms can and do apply to elements. A large collection of Sulphur atoms at STP forms solids of various allotropic forms. At higher temperatures it forms liquids. This is all characteristic of the element Sulphur.
    Individual atoms do represent the element Sulphur, because they all (individually, each and every one) have the properties which cause Sulphur to have these bulk forms.
    For S I don't know. Its a big atom and has many SLG forms. But Hydrogen, I'd bet money that people have worked out enough detail to predict from atomic measurements, what the H-H bond energy would be, telling them that atoms of H will form H2 molecules, then that these will have so little cohesion that they form a gas above a few 10's of K. Or if you regard H2 as a compound of hydrogen, that above say 6000K H atoms will stay separate and be a gas.

    You may have some shred of a point if people were to say, all Sulphur is a solid, or, Sulphur is always a solid, or even, all Sulphur is solid at 20oC, and ultimately, you seem to be saying, if they said, all Sulphur is a solid at 20oC at 1 bar, because they need to add, at least, in macroscopic quantities. But people only add as many of these qualifications as necessary. "Sulphur is a solid" would IMO imply all of the last qualifications, unless circumstances required otherwise. "S is a solid at 70oC" would imply the other conditions, unless again circumstances implied otherwise. And so on. Since S,L,G is a property of bulk matter, I don't think people often think it necessary to add this qualification.

    Many other physical properties are essentially properties of very large numbers of atoms - temperature, coefft of expansion, speed of sound, electrical resistivity, refractive index, density, ... . And we don't find it necessary to say, the resistivity of copper in large enough quantities is 17 nanoohm metres. Or that this is not a property of copper.
    There must of course be a very interesting discussion to be had about how properties change as the number of atoms decreases. In nanoscience I guess this is what people are trying to find out - by experiment and by prediction from the properties of the individual atoms.

    'm sure no one just assumes that materials behave in small groups of atoms just the same as they do in bulk.
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