physics-subatomic-particles

More accurate measurements using x-ray crystallography soon followed these crud eapproximations, and it is now possible to draw up an accurate table of atomic an dionic radii . It was later found that the size of a nucleus consisting of A particle swas given by the approximate equation : d 2r0 1 , where d is the diameter of the nucleus ,and 14 .1 .3 xRutherford's conception of the atom had been to consider it as a miniature solarsystem, with the electrons orbiting, like planets, in ellipses, around the nucleus a tthe centre, acting like a sun . However, such an atom would not be nearly so stable a sobservations of atoms suggested . But in 1913 the brilliant young Danish physicis tNiels Bohr came to Iianchester to work with Rutherford on subatomic structure . Cne o fBohr's greatest a .bitions throughout his life was to produce conditions under whic hinternational cooperation in science could flourish . As the Maxwell-Lorentz theorystated that all electric charges not moving uniformly in a straight line produc elight, all electrons would emit light constantly as they orbited the nucleus i nRutherford's model of the atom . If this were the case the orbiting electrons woul dquickly lose their energy and fall into the nucleus, which was obviously not what wa shappening .The Quantum Theory postulates that all paraicles must have an energy, and hencean angular momentum, of an integral multiple of a small constant known as Planck' sconstant (h) . Angular momentum is the speed at which a body rotates about a fixe dpoint .Bhr realised that because an electron has angular momentum when it revolves i nits orbit around the nucleus, it can only occupy various discontinuous orbits, becauseit must have an energy of an integer multiple of ) (h/?n) . Bohr primarily consideredthe protium (hydrogen) atom, because it was the simplest possible atom . In this atom ,he postulated that the single electron orbits, when the atom is in its normal state ,so that it has an angular momentum of 1X . 'When the atom is excited it changes it sorbit to one where its angular momentum is some integer multiple of greater than one .Bohr suggested that in its 'ground state' the hydrogen atom has an energy of -R ,where R, or, more usually, R„ (denoting an assumption of infinite proton mass) is anew constant called Ryberg's constant . The currently acknowledged value of Roi s1 .0973731(1) x 10 7 m . The reason why the energy of hydroger was said to be negativewas that the electron is in a 'bound state', and an energy value of 0 would indicat ethat the electron and the nucleus were infinitely far apart . Bohr stated that theenergy of a hydrogen atom was -R/n1 , where n was any positive integer . However, th emost revolutionary thing proposed by Bohr in his atomic model was that when th eelectron 'jumps' from a higher to a lower-energy orbit, energy in the form of electromagneticradiation is given off . He found that the frequency of the emitted light wa sgiven by hvA6 . Es - 2A , where v is the frequency, h is Planck's constant, Ea is th eenergy of the higher-energy orbit, and EA that of the lower-energy one . From this i tmay be seen that hvA a corresponds to the line in the spectrum of hydrogen produce dwhen a hydrogen atom loses the energy Ea - E A ,It had been shown by Balmer as early as 1885, that the first four lines of th espectrum of hydrogen had wavelengths in almost exact agreement with the formul a\_ > o n'- /(n 1-4) , where is any constant, and n is a positive integer greater than two .However, no theoretical justification had been found for this formula . But Bohrdiscovered, as a rsiult of the formula hv, . Ea - E mentioned above, that1 1Rr~A$ \n twhere \ A. is the wavelength of the spectral line produced when two positive integers