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What % of an atom is empty?

  1. May 4, 2005 #1
    Recently i read:

    "atoms turn out to be 99.99999999% empty space"

    (source: http://www.futurehi.net/docs/Reality_Consciousness.html [Broken] )

    Is this correct?
    Does a more accurate measurement of the percentage of empty space in an atom exist?
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. May 4, 2005 #2


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    The volume of an atom (roughly 1 angstrom, or 10^-10 m in diameter) is about 15 orders of magnitude larger than the volume of a nucleon (roughly 1 fm, or 10^-15 m in diameter). It seems rather silly to express that ratio in percentage, but it would be 99.9999999999999% (13 nines after the decimal point).

    Of course, the radius of a nucleon is not an absolute figure, since there really is no concept of 'radius' in quantum mechanics. 1 femtometer is a reasonable value. If you're wondering whether anyone has gone out and made a more precise measurement of the size of a nucleon, the answer is no: there's really no such thing as a precise measurement of the size of a nucleon.

    - Warren
  4. May 4, 2005 #3
    Someone told me that, for instance, the nucleus of a hydrogen atom consists of 3 quarks. But that these quarks are considered 'points'.

    If these quarks are 'points', does that imply the nucleon is 99.99i (i=infinite) empty?
  5. May 4, 2005 #4


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    The quarks are regarded as being "point" particles, as are electrons. The nucleons, composed of quarks, do indeed have size, since the quarks they contain never get too close to each other. (This is analogous to the way electrons do not fall into the nucleus -- quantum mechanics forbids it.)

    In the end, if everything in the world is fundamentally composed of point particles, then everything is really entirely "empty" -- the notion of size is then just defined by the distance between such points. This may, in fact, be completely true.

    - Warren
  6. May 5, 2005 #5

    Andrew Mason

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    You first have to define what you mean by empty space. To do that, you have to define what you mean by space that is not empty - ie. what does it mean for space to be full or occupied?

    Most of the space occupied by an atom is inaccessible to other atoms due to the electrical forces between atoms. But it is quite accessible to a freely moving neutron. Most of the space inside the neutrons and protons in the nucleus is inaccessible to all atomic matter. But that space is quite accessible to a neutrino. Whether space is 'empty' or 'occupied' depends on what it is you are trying to penetrate it with.

    In fact, there is no such thing as a 'solid' particle. Solidity is a macroscopic concept. At the atomic level, solidity has no meaning.

    Last edited by a moderator: May 2, 2017
  7. May 5, 2005 #6
    I guess with empty space i mean... um... i dont know really. Any definition i can come up with seems to be flawed.

    Anyway thanks for the answers, things are a little bit more clear to me now.
  8. Mar 2, 2009 #7
    My friends are disturbed to learn that they are 99.9999999999999% empty space! I tell them that, although their bodies are almost entirely empty space, they nevertheless contain an extremely large amount of energy. I would like to reassure them further by telling them approximately how much energy is contained in their bodies. Does anyone have figures for, or know where I can find: (1) how much energy -- nuclear plus other(s)? -- is contained in carbon atoms, hydrogen atoms, oxygen atoms, and the other atoms that make up the human body; (2) the percentages of each relevant atom in the human body; (3) the average number of atoms in a 180-lbs. human body; and (4) a calculation of how much energy is contained in a 180-lbs. human body based on these figures?
  9. Mar 2, 2009 #8


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    Depends on how you were planning to extract the energy.
    Ultimately they contain energy E = mc2 which if M is 80kg is quite a lot.
    Remarkably similair for most living things -
    Oxygen (65.0%)
    Carbon (18.5%)
    Hydogen (9.5%)
    Nitrogen (3.2%)
    And the rest a few metals

    Oxygen has an atomic mass of 16 so there are 1 mole of oxygen atoms in 16g of oxygen.
    1 mole is 6x1023 atoms (quite a lot)
    So 80kg is 5000x 16g = 5000 moles = 5000 * 6x1023 = 3x1027 , that is 3 with 27 '0' after it!

    Atoms don't have an energy as such.
    But using e=mc2 as the total energy in your boy
    E = 80 * 3x108 * 3x108= 7 * x1018 J or about 0.1% of the worlds total energy usage in a year!
    Last edited: Mar 2, 2009
  10. Mar 2, 2009 #9


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    But.. it's full of electrons!

    Electrons don't move around the nucleus like planets orbiting the sun. They can exist at any distance from the nucleus. It's a quantum particle that doesn't have a definite location. In fact, for a hydrogen atom (one electron) the nucleus is in fact the single most probable point to find the electron!

    But remember that's just a single point, it's not the most probable distance. (as you get farther from the nucleus the amount of area where the electron might be increases as 4*Pi*r^2 - the area of a sphere). So, the distance at which the electron is most likely to be is something else.

    For a hydrogen atom, the probability you'll find the electron at a given radius, r, is:
    Where [tex]a_0[/tex] is a constant which happens to be the most probable distance: the Bohr radius; ~0.053 nm.

    So the 'size' of a hydrogen atom is often equated with the Bohr radius. And it is indeed quite large in comparison to the 'size' of the nucleus. But the electron could in fact exist at any radius, not least the ones between 0 and a0. There's about a 1-in-3 chance you'll find the electron there. Or put another way, it spends about a third of its time in between a0 and the nucleus.
  11. Mar 3, 2010 #10
    actually, from my limited understanding of quantum mechanics, their is no "empty space" in the atom. The regions between the electron orbitals have information and is occupied by strings. Is that correct? There is energy and information in this vacuum "empty space" in the form of plank strings. Is that true?
  12. Mar 3, 2010 #11
    Combustion of a single simple sugar molecule (C6H12O6 + 6O2 -> 6H2O + 6CO2) yields about 29 eV.

    Bob S
  13. Aug 15, 2011 #12
    The “empty” space between the nucleus of an atom and the electron may be filled with “dark energy”?
  14. Aug 15, 2011 #13


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    Corvus, I see this is your first post here so you may have missed looking at the rules, which is something you should do if you plan on hanging around.

    Resurrecting a thread this old is called "necroposting" and is against the rules. If you have a similar question to something, or a question that arises from something, in an old thread, start a new thread to ask it.

    That said, I don't have an answer to your question and you're more likely to get an answer if you post a new thread with a subject line something like "dark energy exists inside atoms?"
  15. Oct 11, 2013 #14

    Simon Bridge

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    @PIT2: you were "reading"?... where?

    Reading through the above: depends what you think "empty space" means.

    The statement, if from a pop-science or low-level textbook source, involves a pretty naive definition of "empty" ... i.e. a room is very empty if the volume occupied by it's constituents is small compared with the volume of the room.

    For an atom - you can add up the commonly quoted volumes of the electrons and nuclei and compare with the commonly quoted volume of the atom and see for yourself.

    However, that involves a lot of assumptions.
    i.e. the room may be full of air. So the definition of empty, for common use re rooms, would carry a rider that we are not counting the air in room. For the atom situation this may mean we are not counting the electromagnetic field ferinstance. Also assumptions about the overall state of the atom and what counts as part of the atom.

    Bottom line: it depends on how you look at it.

    I recall a practical demonstration given to 1st year college physics students ... they were given a bunch of objects and asked to rank them according to size. Different groups used different criteria, which were discussed afterwards ... but everyone ranked the golf ball at the small end and the 1.5m wooden rod at the bigger end. The professor than asks everone to re-evaluate their choices based on the criteria that the object has to pass through a garden sieve he had with him. Only the rod would fit... making it small. i.e. crossection counted.

    You'd think that the crossection for an atom is the same no matter what - since it's basically a ball right? But the crossection that is important depends on the sieve as well ... for the atom, the sieve is what we are looking at the atom with. You get different descriptions if we look with electrons or alpha particles ... or what energy the beam is set at... and so on.

    So you see: the reason for varying replies is that the question is too vaguely worded.
  16. Oct 12, 2013 #15


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    Simon, just fyi, this thread is from May 2005 and has been necro'd 4 times by my count.
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