Structure of the Atom Part I continued What IS the structure of an atom What are the properties of atoms REMEMBER structure affects function Important questions Where are the electrons What is the energy of an electron Dual Nature of Light c E h Line Spectrum Bohr Model of Hydrogen Atom Mary J Bojan FA 2010 1 Quantized Energy Energy comes in discrete packets or quanta Energy of a quantum is h frequency of light h Planck s constant 6 63 10 34 J s Total energy in light beam is nh n 1 2 3 Dual Nature of Light Wave c Particle E h Experimental support black body radiation Planck 1900 photoelectric effect Einstein 1905 line spectra of hydrogen Bohr 1913 Mary J Bojan FA 2010 2 Classically expect metal to soak up energy of light until e binding energy Eb is overcome BUT No e s emitted until 0 No waiting time Kinetic energy of e h 0 mv2 where v speed of electron emitted Metal atoms absorb only 1 quantum of energy it happens all at once as if struck by a particle photon Ephoton h Eb mv2 Mary J Bojan FA 2010 3 When light of wavelength 420nm is focused on a metal surface electrons are ejected with a speed of 7 50 x10 5 m s What is the binding energy of the electron in the metal Mary J Bojan FA 2010 4 Line Spectra of Atoms Spectroscopy study of light interacting with matter Spectrum distribution of in emitted radiation Spectrum Type Monochromatic Continuous Discrete or line s Examples DEMONSTRATIONS How can we explain all of this Mary J Bojan FA 2010 5 Line spectra Hydrogen Mary J Bojan Neon FA 2010 6 Observation of line spectra implies that atoms have discrete quantized energy levels Mary J Bojan FA 2010 7 n 1 2 3 principal quantum number RH Rydberg constant 2 18x10 18J Mary J Bojan FA 2010 8 Energy of an Electron Bohr Model Energy is given off when an electron is put into orbital Coulomb s Law helps where Q1 charge of electron negative Q2 charge of proton positive d orbit radius distance between nucleus and electron Put electron into the orbital attractive interaction Energy will be negative means energy is given off Reverse the process try to remove the electron Energy will be positive energy is absorbed Note Orbit energy in Bohr Model is negative so it must correspond to energy needed to put electron into the orbit Mary J Bojan FA 2010 9 Line spectrum is due to electronic transitions Atoms absorb or emit light when e changes its orbit E Ef Ei h where ni and nf are integers This predicts the H atom spectrum EXACTLY Note nf ni nf ni Mary J Bojan E is E is absorbs photon emits photon FA 2010 10 Problem Solving Bohr Model If ni 2 and nf 1 is energy emitted or absorbed 1 emitted 2 absorbed Of the following transitions in an H atom which one results in the emission of the highest energy photon 1 n 1 n 6 2 n 6 n 3 3 n 3 n 6 4 n 1 n 4 5 n 6 n 1 Mary J Bojan FA 2010 11 From Orbits to Orbitals Bohr model explained some experimental evidence for hydrogen atom but it failed for other atoms DeBroglie 1924 if light has dual wave particle behavior perhaps matter does also Wavelength of matter waves h mv Electron waves discovered in 1927 Davidson and Garmer Basis for electron microscope For a baseball and bacteria is too small to observe but for electrons is of atomic size producing profound effects Electrons in atoms behave as standing waves Schr dinger equation 1926 Enter the Quantum World Mary J Bojan FA 2010 12 Electron microscope Used to image some of the tiniest objects Electrons diffract when interacting with matter Image of HIV budding from T cell Mary J Bojan FA 2010 13 At what velocity must a neutron which weighs 1 67 10 24 g be moving in order for it to exhibit a wavelength of 400 pm A B C D E Mary J Bojan 9 92 102 m s 9 92 10 1 m s 9 92 101 m s 9 92 104 m s 9 92 103 m s FA 2010 14 Heisenberg Uncertainty Principle It is NOT possible to simultaneously know the position velocity momentum mv of a particle with complete certainty Derives from wavelike nature of matter This really becomes important when dealing with subatomic matter All electrons have a velocity therefore you cannot specify their exact location It is not appropriate to imagine e moving in nice little orbits around the nucleus Contradicts Bohr s planetary model of the hydrogen atom Can we say anything about where the e are Mary J Bojan FA 2010 15 H E x y z wavefunction no physical significance 2 x y z probability of finding one electron in a region of space also called electron density Think of electrons as clouds of electron density Orbitals 2 x y z Mary J Bojan FA 2010 16 Tells us WHERE the electron is Tells us the ENERGY of the electron An orbital specifies the probability of finding an electron in a given region of space i e orbitals have shapes specifies the energy of the electron is characterized by quantum numbers 3 of them Mary J Bojan FA 2010 17 Classical waves Only certain stable modes are allowed Modes characterized by an integer number of nodes 1 for each dimension Equal degenerate s appear in 2 3 D due to symmetry Mary J Bojan FA 2010 18 3 D expect 3 quantum numbers n and m 1 Principal quantum n Mary J Bojan FA 2010 19 Mary J Bojan FA 2010 20 Quantum Numbers 2 Azimuthal quantum Use symbols rather than numbers for Mary J Bojan 0 1 2 FA 2010 3 21 3 Magnetic quantum number m Mary J Bojan FA 2010 22 22 Summary Orbitals Allowed energy states for electrons in atom Describes spatial distribution of electrons in these energy states Orbital name number of orbitals shape s p d f 1 3 5 7 Quantum Numbers n m principal azimuthal magnetic Mary J Bojan spherical dumbell clover leaf defines size shape orientation FA 2010 23 Shells Subshells Orbitals n2 number of states number of orbitals in the nth shell Subshells 1s of orbitals 2s 2p 3s 3p 3d 4s 4p 4d 4f orbitals in each subshell Mary J Bojan FA 2010 24 Shells Subshells Orbitals Shell defined by Subshell defined by Example 3s 2p quantum number quantum numbers n 3 0 n 2 1 Orbitals of the same subshell have the same energy they are degenerate Orbital defined by Example quantum numbers 2px n 2 1 2py n 2 1 2pz n 2 1 and m 1 0 1 when 1 Note All of these have the SAME energy Mary J Bojan FA 2010 25 Structure of the Atom Part II Orbitals Quantum Numbers Multi electron Atoms Spin Quantum Number ms Pauli Exclusion Principle Hund s Rule Electron Configurations using the Periodic Table …
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