Ch 6 Electronic Structure of Atoms Electronic structure The arrangements of electrons in atoms o Number of electrons in the atom as well as distribution around the nucleus and their energies 6 1 The Wave Nature of Light Electromagnetic radiation Also known as radiant energy light emitted or absorbed by substances o All types move through vacuum at 2 998 x 10 8 m s speed of light Periodic Pattern of peaks and troughs repeats itself at regular intervals o Wavelength Distance btwn two adjacent peaks o Frequency Number of complete wavelengths or cycles that pass a given point each second units are hertz Inverse relationship between frequency and wavelength of EM radiation o v c wavelength x frequency speed of light Electromagnetic spectrum Display showing various times of EM radiation arranged in order of increasing wavelength 6 2 Quantized Energy and Photons The emission of light from hot objects blackbody radiation The emission of electrons from metal surfaces on which light shines photoelectric effect The emission of light from electronically excited gas atoms emission spectra Hot Objects and the Quantization of Energy Max Planck 1858 1947 o German physicist o 1900 proposed energy can be released or absorbed by atoms only in discrete chunks o Quantum fixed amount Smallest quantity of energy that can be emitted or absorbed as EM radiation o E hv E energy of single quantum v frequency Planck constant 6 626 x 10 34 J s o Energy emitted or absorbed only in whole number multiples of hv o Allowed energies are quantized values restricted to certain quantities o 1918 Nobel Prize in Physics for work on quantum theory The Photoelectric Effect and Photons Albert Einstein 1879 1955 o Photoelectric effect 1905 use of Planck s theory to explain electrons emitted from metal surfaces Photon Packet or particle of energy Energy of photon E hv Radiant energy is quantized Photons can transfer energy to electrons in metal Work function Amount of energy required for electrons to overcome attractive forces holding them in metal Intensity brightness of light related to number of photons striking but not E of each photon Nobel Prize in 1921 for photoelectric effect 6 3 Line Spectra and the Bohr Model 1913 Danish physicist Niels Bohr explained line spectra using ideas of Planck and Einstein Line Spectra Monochromatic Radiation composed of a single wavelength Polychromatic Radiation composed of many different wavelengths most sources Spectrum Display of radiation separated into component wavelengths Continuous spectrum Rainbow of colors containing light of all wavelengths Ex Red orange glow from neon yellow from sodium Line spectrum Spectrum containing radiation of only specific wavelengths o Line spectrum of H found in mid 1800s 1885 Swiss Johann Balmer found equation relating wavelengths to integers o Balmer equation extended to Rydberg equation wavelength RH Rydberg constant 1 096776 x 107 m 1 n1 and n2 positive integers Bohr s Model Bohr assumed electrons in H atoms move in circular orbit around nucleus but electron does not lose energy as it should Model based on three postulates o Only orbits of certain radii corresponding to certain specific energies are permitted for the electron in a H atom o An electron in a permitted orbit is in an allowed energy state It does not radiate energy and does not spiral into nucleus o Energy emitted or absorbed by electron only as electron changes from one allowed energy state to another Energy E hv The Energy States of the Hydrogen Atom Energies corresponding to allowed orbits for electron in H atom o o Principal quantum number Integer n which can have whole number values Radius of orbit gets larger as n increases The lower most neg the energy is the more stable the atom is Ground state Lowest energy state n 1 Excited state Higher energy state n 2 or higher Reference Zero energy state in which electron is completely separated from nucleus Energy absorbed to move to higher energy state and emitted when electron jumps to lower energy state The energy of the photon Ephoton must equal the difference in energy btwn the two states E Limitations of the Bohr Model Electrons exist only in certain discrete energy levels which are described by quantum numbers Energy is involved in the transition of an electron from one level to another 6 4 The Wave Behavior of Matter Louis de Broglie 1892 1987 o French physicist o o Momentum Quantity mv for any object o Matter waves Wave characteristics of material particles o Any object of mass and velocity would give rise to a characteristic matter wave X ray diffraction Interference pattern characteristic of wavelength properties of EM radiation that forms when X rays pass through a crystal The Uncertainty Principle Werner Heisenberg o German physicist o Uncertainty principle Impossible to simultaneously know both the exact momentum of the electron and its exact location in space o 6 5 Quantum Mechanic and Atomic Orbitals Erwin Schrodinger 1887 1961 o Schrodinger s wave equation Incorporates both wave like and particle like behaviors of electron o Standing waves Waves that do not travel in space Appendix