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P3A3B Atomic Physics Notes 2013 1 Coghlan Atomic Physics Notes Light is an example of _____________ radiation which transfers _____________ at 3.00 x 108 m s-1. The electromagnetic _____________ is the _____________ of all _____________ of this type. A ray or beam of light actually consists of two _____________ fields – _____________ and _____________ – hence – electromagnetic. These two fields are _____________ at _____________ angles. Its _____________ is the length of one oscillation or _____________ or energy pulse. Its _____________ is how many times the _____________ oscillate per second. http://micro.magnet.fsu.edu/primer/java/polarizedlight/emwave/ http://www.colorado.edu/physics/2000/microwaves/water_rotates.html P3A3B Atomic Physics Notes 2013 2 Electromagnetic radiation Coghlan Production radio waves e- _____________ up and down a radio mast micro waves e- oscillating in a _____________ cavity (magnetron) IR, visible, UV e- oscillating within _____________ & _____________ X-rays e- rapidly _____________ gamma rays e- oscillating in the _____________ http://lectureonline.cl.msu.edu/~mmp/applist/Spectrum/s.htm Nature of Light Wave Particle Duality http://www.colorado.edu/physics/2000/schroedinger/two-slit3.html Newton 1671 _____________ model for light light behaves like a _____________ _____________ explains most properties of light except _____________ and interference Huygens 1678 wave model http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html Young 1801 double slit _____________ experiment supported the wave model Maxwell 1865 - complete wave theory for light extended to all _____________ radiation P3A3B Atomic Physics Notes 2013 3 Coghlan Photoelectric effect http://www.colorado.edu/physics/2000/quantumzone/photoelectric.html The Photoelectric effect is the _____________ of an e- from a _____________ (usually metal) when _____________ radiation (usually light) shines on it. For the photoelectric effect, the following observations were made; - there is a certain _____________ frequency below which no _____________ were emitted - _____________ the threshold frequency, the _____________ the light the more photoelectrons emitted - there was no time de_____________ lay between irradiation and _____________ - if f is increased, EK of the _____________ increases The wave model was _____________ in explaining the photoelectric effect! If the wave model is true, then X - any frequency light should cause photoemission - - for lower frequencies there should be a time delay between irradiation and photoemission - - X the brighter the irradiation, the more the photoelectrons – X. P3A3B Atomic Physics Notes 2013 4 Coghlan Max Planck 1900 light energy is not _____________ light energy is delivered in tiny, _____________ bundles of energy called _____________ or _____________ the energy of the photon is _____________ to its frequency. Where E=hf E energy, J h Planck’s constant, 6.63 x 10-34 J s f frequency of photon, Hz The current view of light is that it possesses both _____________ and _____________ properties and which properties light in fact exhibits depends on the _____________ used to look at it. Atomic Structure http://www.rsc.org/chemsoc/timeline/pages/1911.html http://www.walter-fendt.de/ph14e/bohrh.htm http://www.colorado.edu/UCB/AcademicAffairs/ArtsSciences/physics/PhysicsInitiative/Physics2000/a pplets/a2.html http://csep10.phys.utk.edu/astr162/lect/light/bohr.html Neils Bohr 1913 e- exist in atoms in _____________ levels n = 1, 2, 3, 4…… the energy of the e- is _____________ – it can only have _____________ values e- in one energy level can jump to another level by the _____________ or _____________ of a _____________ P3A3B Atomic Physics Notes 2013 5 Coghlan the energy of such a photon = E between the _____________ levels lowest energy _____________ for an atom is called its _____________ state any other electron _____________ for an atom is its _____________ state. http://www.physics.uoguelph.ca/applets/Intro_physics/kisalev/java/atomphoton/index.html Consequently, an e- in an atom may _____________ from a _____________ allowed energy level to a lower one by _____________ just the _____________ amount(quantum)of energy (photon). LINE EMMISION SPECTRUM http://csep10.phys.utk.edu/astr162/lect/light/absorption.html http://jersey.uoregon.edu/elements/Elements.html Such _____________ emission spectra are _____________ for every elemental gas because every element has its own particular set of _____________ energy _____________ and hence only certain energy _____________ are _____________ from the excited atom. http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf Ex/ How many emission lines in a line emission spectrum would be produced by a gaseous atom excited by an electric field if its available energy levels are shown in the diagram? Ground state electrons in such an electric field continually _____________ just the right _____________ of energy to jump to a P3A3B Atomic Physics Notes 2013 6 Coghlan higher _____________ state (an _____________ state) and then fall back down to the _____________ state in one or more jumps from allowed energy state to allowed energy state. The ground state for valence electron represents a _____________ energy situation for an atom. Energy of electron 0 Distance from nucleus The energy levels allowed for the electron to access can be represented by a ladder diagram. Ionisation Many close levels E4 E3 E2 E1 An atom in the ground state is an _____________ atom. If an electron gains too much energy, it will _____________ the atom and an ion will be made. E0 Ground state Energy is _____________ to excite the atom. Energy is _____________ as _____________ when the excited electron _____________ back down to the _____________ state. http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/quantumzone/bohr2.htm l e- in an atom may _____________ level to a _____________ from a lower _____________ one by _____________ amount(quantum) of energy (_____________). energy just the correct P3A3B Atomic Physics Notes 2013 7 Coghlan LINE ABSORPTION SPECTRUM http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/quantumzone/lines2.ht ml Photon absorption To become excited, a ground state electron may _____________ a photon. However a ground state electron will only _____________ a photon if the photon’s energy _____________ corresponds to the energy _____________ for that electron to jump to one of its _____________ higher states. Ex/ A gaseous Hg atom is being irradiated with photons of many different energies. (a) Ionisation What energy photons may be absorbed? What energy photon causes ionisation? (c) What frequency would the -8.83 x 10-19 J Ground state photon in (b) possess? (d) -5.94 x 10-19 J Energy of e- (b) 0 -2.50 x 10-19 J -16.6 x 10-19 J What type of spectrum would be produced by this situation? (e) Not counting the ionisation energy, how many lines would be produced in the spectrum and what would be their colours? http://www.physics.uoguelph.ca/applets/Intro_physics/kisalev/java/laser/ Electron bombardment(scattering) http://www.matter.org.uk/tem/electron_scattering.htm If an atom is bombarded with electrons, _____________ or _____________ collisions between bombarding electrons and electrons in the _____________ state may occur. That is the bombarding P3A3B Atomic Physics Notes 2013 8 Coghlan electrons may give up _____________ or _____________ or _____________ of their EK and are then _____________ often with reduced EK. Ex/ 8.00 eV electrons bombard an atom in Energy of e- Ionisation 0 -1.80 eV its ground state. -2.10 eV the scattered electrons, and -4.70 eV (b) (a) Calculate; the energies and velocities of the frequencies of the emitted photons and their colours. Ground state Note: -10.0 eV E = V q 1.00 eV = 1.60 x 10-19 J Mass of electron = 9.12 x 10-31 kg P3A3B Atomic Physics Notes 2013 Types of Spectra 9 Coghlan http://www.astrophys-assist.com/educate/solarobs/ses01p11.htm There are three main types of spectra – _____________, _____________ and _____________ . Continuous Spectrum Line absorption spectrum Line emission spectrum Hot Gaseous element Cool Gaseous element energises Hot source Liquid or Solid energises Hot Gaseous molecules Cool coloured solution or transparent coloured solid Band absorption spectrum Band emission spectrum http://www.antarcticconnection.com/antarctic/weather/aurora.shtml Spectral analysis http://www.astro.uiuc.edu/~kaler/sow/spectra.html#absan Each element has its own _____________ emission/absorption _____________. A mixture of elements generating an _____________ /_____________ spectrum will retain all the _____________ from each element. An atomic absorption _____________ can be used to obtain an absorption spectrum from a sample and by _____________ lines, _____________ the _____________ elements in the sample. http://www.learner.org/teacherslab/science/light/color/spectra/ http://www.aurora-instr.com/ai1200.htm P3A3B Atomic Physics Notes 2013 10 Coghlan The black Fraunhöfer lines seen in the sun’s _____________ spectrum are caused by absorption of _____________ by _____________ in the sun’s _____________. Similar analysis can be performed for other stars and also for planets using light from stars that just _____________ a planet’s surface. Luminescence Luminescence is the _____________ of light by a _____________ not due to the _____________ of the material. Luminescence caused by photons electrons living thing chemical reaction Bioluminescence Photoluminescence Electroluminescence may show Chemiluminescence may show Fluorescence or Phosphorescence The excited material emits one or more photons in a very short period of time ( 10-8 s) and returns to ground state producing a line or band emission spectrum. e.g. whiteners, fluorescent tube. A phosphorescent material has a metastable excited state in which the excited electron remains in a higher energy level for an extended period of time (up to 8 hours). It produces a line or band emission spectrum. e.g. watch dials, TV screens, toys. http://mineral.galleries.com/minerals/property/fluoresc.htm P3A3B Atomic Physics Notes 2013 11 http://www.lifesci.ucsb.edu/~biolum/ Coghlan http://www.shsu.edu/~chm_tgc/chemilumdir/chemiluminescence2.html Whiteners http://www.seventhgeneration.com/household_hazards/optical_brighteners.php Over time, _____________ paper and _____________ becomes more yellow. Intensity Old Intensity New Red Violet Red Frequency Violet Frequency An _____________ brightener can return the yellow fabric to white temporarily. These optical brighteners (usually contained in _____________ powder)are excited by _____________ radiation and when the _____________ return to _____________ state, they primarily emit _____________ in the blue-violet part of the spectrum and thus return the _____________ spectrum and the fabric appears white again. Energy of e- Ionisation Ground state P3A3B Atomic Physics Notes 2013 12 Coghlan X-Rays Röentgen, 1895 Produced in two ways. (1) High energy _____________ (> 40 keV) slowed down by _____________ with a _____________ atom (high m.p. metal) and being _____________ with a lower energy – the energy _____________ equal to the X-ray Intensity energy of the X-ray _____________ produced. Because many _____________ frequency X-ray photons can be produced in this way, an Xray _____________ is _____________. Wavelength (2) electron and _____________ from a _____________ falls into this by the incident X-ray Intensity _ level electron excited the atom. The higher An e- energy level _____________ lower energy level and an _____________. ____________ X-ray photon is Wavelength _____________ is filled by _____________ e-. energy level eBecause of the _____________ of energy levels, only _____________ frequency Xrays can be generated in this way. So a typical X-ray spectrum is a _____________ spectrum with one or more _____________ characteristic of the target _____________. http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/xray/making_xrays.htm l P3A3B Atomic Physics Notes 2013 13 Coghlan only 1% of incident e- produce X-rays, the _____________ appears as _____________. Much of the _____________ e- EK is lost and heat is produced X-ray; 0.1 nm f 3 x 1018 Hz Only _____________ X-ray photon is produced from _____________ einteraction with a _____________ energy level electron but _____________ than one photon from one _____________ incident may be produced. http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/xray/making_xrays2.ht ml The _____________ anode is typically made from _____________ tungsten which is often _____________ in copper (to help heat conductivity) and _____________ cooled to stop the tungsten from _____________. P3A3B Atomic Physics Notes 2013 14 Coghlan Energy of electron: W = q V Highest energy x-ray = q V h fmax = q V fmax = q V h fmax = q V h Where fmax maximum frequency of x-ray produced, Hz q charge on electron, C V acceleration potential difference, V h Planck’s constant, 6.63 x 10-34 J s http://www.antonineeducation.co.uk/Physics_A2/Options/Module_6/Topic_7/topic_7_x.htm Ex/ Calculate the cut-off wavelength for the X-ray spectrum produced by electrons that are accelerated through a potential difference of 65.0 kV. P3A3B Atomic Physics Notes 2013 15 Coghlan Applications of X-rays http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/xray/xray_abs1.html http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/xray/xray_abs2.html http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/xray/xray_abs3.html http://www.colorado.edu/physics/2000/xray/ Medical – the more _____________ the material the greater the xray _____________ - can vary the x-ray energy hence vary the image quality - protection needed – _____________ radiation - dentist – _____________ aprons - veterinarians - cancer treatment Industry – inspection of metal joins, welds, castings Crystallography – structure of molecules, crystals.