Which of the following is true regarding the Bohr model? QUESTION: Which of the following is true regarding the Bohr model? A. it assumes that electrons move around the nucleus in elliptical orbits B. it only works for atoms or ions with only one electron C. it assumes that electrons will eventually crash into the nucleus D. it predicts that light is produced when an electron transfers from a smaller orbit to a larger orbit CIRCULAR H, He+, Li2+, Be3+, B4+ SCRIPT Which of the following is true regarding the Bohr model? A. it assumes that electrons move around the nucleus in elliptical orbits B. it only works for atoms or ions with only one electron C. it predicts that electrons will eventually crash into the nucleus D. it predicts that light is produced when an electron transfers from a smaller orbit to a larger orbit Let’s examine each of the choices given. Choice A is wrong. CLICK Bohr’s model assumes circular orbits, not elliptical orbits CROSS OUT ELLIPTICAL Choice B is correct. Bohr’s model only works for the hydrogen atom, or ions with one electron, such as He+, Li2+, It doesn’t work for atoms with more than one electron like Helium. However, it will work for He+ ion, since He+ only has one electron This is the reason why Bohr’s model eventually had to be discarded. Choice C is wrong. The physics known at that time predicts that …. Because electrons moving around the nucleus are accelerating… They would be continually losing energy by emitting light…. And that they would eventually crash into the nucleus… The nuclear atom suggested by Rutherford’s experiment,… with negative electrons circling a positive charged nucleus … could not be stable and should not exist. Bohr made a bold assumption that electrons only stay in certain orbits that happen to be stable. For example, in the case of hydrogen, he predicted that the radius of the nth orbit is 52.9 picometers, times n squared. Choice D is wrong. It should say from a higher orbit… to a lower orbit. A higher energy is associated with a higher orbit. So when an electron transfers from a higher orbit to a lower orbit, it loses energy in the form of light. The energy of the photon produced is equal to the difference in the energy associated with the two orbits. Assumed electrons stay in allowed orbits For H: nth orbit has a radius of 52.9n2 pm E photon = E = E higher orbit – E lower orbit

Video ID: 2-2-1 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08