January 3 – Rutherford's Physics Trumps Alchemy

nPostednon January 3, 2015

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This sculpture of Rutherford “splitting the
atom” and discovering the nucleus (although
in reality, he wore clothes as he did his
famous experiments) is found in Eastern
China, in the Qingpu Oriental Land Garden.

nForncenturies people had tried to create gold—precious, beautiful,nheavy, shiny gold—out of “base metals.” All the greedyntinkering with materials in this attempt—experimentalnmessing-around that went by the name alchemy—actualngrew into the experimental methods of an actual science, chemistry.n(Do you see the relation of the words alchemynand chemistry?)nn

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nBut,nit turns out, no amount of chemical tinkering can turn one element,nsuch as lead, into another. No gold for the alchemists, no matter hownhard they tried!

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nOnnthis date in 1919, Ernest Rutherford did not create gold out ofnanother element, but he did use gold foil in his experiment, and hendid succeed in—for the first time ever—using science to changenone element into another:

nHe sent alpha particles through thin gold foil and into pure nitrogen.

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And he created oxygen.

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n(Alphanparticles are helium nuclei: two protons and two neutrons. Actually,nwhen Rutherford sent the helium nuclei into pure nitrogen, he notnonly created oxygen but also leftover protons.)

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nThisnwas an incredible step forward for physics, but in a way it is all ofna piece with Rutherford’s other accomplishments. Because ofnRutherford’s experiments with radioactive materials, the gold foilnexperiment, and later a fully controlled splitting of a nucleus,nRutherford was able to develop a model for atoms that was much morenaccurate than earlier models.

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nUm…whatnexactly are atoms? n

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nMatternis largely made up of atoms. In the way olden days, people used atomnto mean the smallest possible quantity of matter, which could not benfurther divided.

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nIndivisible?nThen…why do we need a model? If it’s indivisible, how could therenbe structure?

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nOfncourse, the important words in the last sentence are “in the waynolden days.” Modern scientists of the early 1900s knew that therenmust be structure in atoms, and although they could not be divided bynchemical means, Rutherford showed that natural radioactivity was innfact atoms disintegrating into smaller parts. Theoretically, humansncould deliberately “split atoms.”

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nSonwhat model of atomic structure did scientists come up with?

nInn1904 J. J. Thomson suggested the plum pudding model of an atom. n

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nElectronsnhad been discovered in 1894, and Thomson suggested that thennegatively-charged electrons were scattered about in a sort ofnpositively-charged “soup” or pudding, like raisins in plumnpudding or blueberries in muffin batter.

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nAndnRutherford disproved this model?

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WhennRutherford ran his gold foil experiment, he hypothesized that thenalpha particles would continue through plum-pudding atomsnuninfluenced by their consistent “mixture” type of structure.nHowever, he discovered that a small portion of alpha particles werendeflected, which would only make sense if the positive charge in annatom was found only in a small central area rather than throughoutnthe entire atom.

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nDonwe still use Rutherford’s model?

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nYesnand no. Thanks to Rutherford and Niels Bohr, we know that protons (+ncharge) and neutrons (no charge) are in a central nucleus, but ournquantum physics insists that this familiar looking atomic model,nwhich has electrons orbiting the nucleus rather like planets orbitnthe sun…

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n…isntoo simplistic. Instead, electrons form a “probabilistic” cloudnaround the dense nucleus. n

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nButnquantum physics is hard to draw or even think about. Most “structure of the atom” model-making activities go back to the simplernRutherford-Bohr model.

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nAlsonon this date: