Lecture 3 Electronic structure of an atom Read HW BLB 2 1 2 2 6 1 6 3 BLB 6 4 10 13 23 26 Sup 6 1 3 4 5 do NOT do Sup 6 2 Know E h c photons quantized energy photoelectric effect line spectra Bohr model electronic transitions Exam 1 Monday Feb 9 6 30 Form a study group use the CRC take advantage of SI info on web use the online resources and work those problems practice practice practice Bonus deadline for Skill Check Tests 3 4 is Jan 29 Drop add ends Wednesday Jan 21 Sheets Page 1 Lecture 3 Examples a What is the frequency of light if 450 nm c c b What is the energy of one photon of 450 nm light h 6 63 10 34 J s E h NOTE E h is only for the energy of 1 photon c What is the energy of 1 mole of photons of 450 nm light You ll see these concepts again when we hit BLB Chap 18 throughout the semester Sheets Page 2 Lecture 3 Photoelectric effect direct observation of quantum effects Einstein 1921 Nobel Prize electrons are emitted by metal only if light has frequency i e energy greater than certain minimum value regardless of light intensity when electrons are emitted the number emitted is proportional to the light intensity Ek h Eb Ek kinetic energy of photoelectron E 1 2 mv2 h photon energy Eb binding energy Sheets Page 3 Lecture 3 Line spectra of atoms spectroscopy study of light interacting with matter spectrum distribution of frequency in emitted radiation spectrum type monochromatic continuous discrete or line Sheets s 1 all a few Page 4 example lasers hot solids gaseous atoms Lecture 3 Atomic spectra cont observation of line spectra implies that atoms have quantized frequencies energy levels in other words atoms can have only preset energy values most energy values cannot occur only certain energy changes are possible for electrons frequencies reflect of atoms atoms have characteristic frequencies Sheets Page 5 Lecture 3 Bohr model of H atom 1 atom is similar to planetary system with e orbiting central nucleus p 2 usual laws of physics hold except that only certain specific radii orbits are allowed n 1 2 3 4 3 energies of the allowed states are 1 E n RH 2 n n 1 2 3 4 RH Rydberg constant 2 18 10 18 J n integer principal quantum number as the allowed radii increase in a quantal fashion by n2 E decreases by 1 n2 NOTE En is always negative Sheets Page 6 E Q1Q 2 d Lecture 3 Electronic transitions in hydrogen ground state is most stable with the largest lowest negative energy Sheets Page 7 Lecture 3 Bohr model of H atom cont 4 atoms absorb or emit light of specific frequency when e changes its orbit i e a photon E Efinal Einitial h or 1 1 h RH 2 2 ninitial nfinal where ninitial and nfinal are integers of orbits predicts the H atom spectrum exactly if nfinal ninitial then E is a photon if nfinal ninitial then E is a photon Sheets Page 8 Lecture 3 Example What is the energy of an electron in a hydrogen atom with the principle quantum number of 6 A B C D E Sheets 6 06 10 20 J 3 63 10 19 J 6 06 10 2 J 3 63 10 19 J 6 06 10 20 J Page 9 Lecture 3 Example Which of the following electronic transitions of the hydrogen atom emits a photon of the shortest wavelength A B C D E Sheets n 6 n 3 n 1 n 2 n 3 n 2 n 2 n 1 n 2 n 4 Page 10 Lecture 3 Before next class Read HW BLB 6 3 6 6 BLB 6 33 39 51 54 Sup 6 6 7 8 10 no Sup 6 9 Know matter waves uncertainty principle electronic transitions of orbitals quantum numbers n m ms orbitals their shapes and energies Answers p 2 a 6 67 1014 s 1 b 4 42 10 19 J c 266 kJ p 9 A p 10 D Sheets Page 11 Lecture 3
View Full Document
Unlocking...