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While in this case, the microscope is apparently producing a magnified image of a hydrogen atom's orbital structure, it is possible for an atom to have a macrsc

While in this case, the microscope is apparently producing a magnified image of a hydrogen atom's orbital structure, it is possible for an atom to have a macrscopic size, although it normally only happens in deep space. It turns out that the mean radius if an electron relative to the proton in a hydrogen atom scales with the square of the principle quantum number, n [1]. Since the energy scales with one over the square of n, high-n states all have energies close to zero. A very tenuously bound electron, with a very large n, can reach macroscopic size scales. While the ground state of hydrogen is the only truly stable state, in tenuous environments with low collision rates, atoms can get "stuck" in excited states that only have very rare radiative transitions available. These sorts of very excited atoms are called Rydberg atoms [2]. [1] http://info.phys.unm.edu/~ideutsch/Classes/Phys531F11/ProblemSets/Phys531_PS01.pdf http://info.phys.unm.edu/~ideutsch/Classes/Phys531F11/Proble... [2] http://en.wikipedia.org/wiki/Rydberg_atom http://en.wikipedia.org/wiki/Rydberg_atom

steve19 13y ago
Theoretically, how wide could an atomic radius get in deep space? Or does that mean that there is an infinitesimally small chance a electron could be found very far away from the nucleus because there is nothing else for it to interact with in empty deep space? (The physics problem you linked to is far beyond my understanding)
- ngoldbaum 13y ago
  I'm honestly not sure how large atoms can be, since there are an arbitrarily large number of high-n states in the limit where the electron is tenuously bound to the proton. I know that states with n ~ 100 are commonly observed (see Figure 3 of [1]) in Galactic and extragalactic star forming regions. This is because ionizing radiation creates a population of relatively recently recombined atoms where the electron happened to arrive in a high-n state. It's not that the electron has an infinitesimally small chance to be observed far away from the nucleus - it's quite likely actually if it lives in a high-n state - it's that collisions rates are so low that the system is out of thermodynamic equilibrium. Section III of these notes [2] describe the physics of Rydberg aroms and the radio recombination lines we observe from them quite nicely. [1] http://iopscience.iop.org/0004-637X/549/2/979/pdf/52126.web.pdf http://iopscience.iop.org/0004-637X/549/2/979/pdf/52126.web.... [2] http://www.ucolick.org/~krumholz/courses/spring10_ast230/notes9.pdf http://www.ucolick.org/~krumholz/courses/spring10_ast230/not...

steve19 13y ago

Theoretically, how wide could an atomic radius get in deep space? Or does that mean that there is an infinitesimally small chance a electron could be found very far away from the nucleus because there is nothing else for it to interact with in empty deep space? (The physics problem you linked to is far beyond my understanding)

ngoldbaum 13y ago
I'm honestly not sure how large atoms can be, since there are an arbitrarily large number of high-n states in the limit where the electron is tenuously bound to the proton. I know that states with n ~ 100 are commonly observed (see Figure 3 of [1]) in Galactic and extragalactic star forming regions. This is because ionizing radiation creates a population of relatively recently recombined atoms where the electron happened to arrive in a high-n state. It's not that the electron has an infinitesimally small chance to be observed far away from the nucleus - it's quite likely actually if it lives in a high-n state - it's that collisions rates are so low that the system is out of thermodynamic equilibrium. Section III of these notes [2] describe the physics of Rydberg aroms and the radio recombination lines we observe from them quite nicely. [1] http://iopscience.iop.org/0004-637X/549/2/979/pdf/52126.web.pdf http://iopscience.iop.org/0004-637X/549/2/979/pdf/52126.web.... [2] http://www.ucolick.org/~krumholz/courses/spring10_ast230/notes9.pdf http://www.ucolick.org/~krumholz/courses/spring10_ast230/not...