PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 4612C1403 Lecture 13, Wednesday, October 19, 2005Chapter 17 Many-Electron Atoms and Chemical Bonding17.1 Many-Electron Atoms and the Periodic Table (Done)17.2 Experimental Measures of Orbital Energies17.3 Sizes of Atoms and Ions17.4 Properties of the Chemical Bond17.5 Ionic and Covalent Bonds17.6 Oxidation States and Chemical Bonding3Summary: The Periodic Table built up by electron configurations: the ground state electron configurations of the valence electrons of the elements417.2 Experimental Measures of Orbital EnergiesPhotoelectron spectroscopy. Measuring the energy of electrons in orbitals by kicking them out with photonsPeriodic trends in ionization energies and electron affinitiesEffective nuclear charge and screening by inner electrons. How these influence ionization energies and electron affinitiesIonization energies. How strongly atoms hold on to electronsElectron affinities. How strongly atoms add an electron5En = -(Zeff2/n2)Ry = energy of electron in orbitalrn = (n2/Zeff)a0 = “average” radius of a orbitalThe Bohr one electron atom as a starting point for the electron configurations of multielectron atoms.Some important periodic properties of atoms:Energy required to remove and add an electron (En)Size of atoms (rn)Rules: (1) Larger Zeff more energy required to remove e-(2) Smaller r more energy require to remove e-Replace Z (actual charge) with Zeff (effective charge)6Rule: In many electron atoms, for a given value of n, the value of Zeff decreases with increasing l, because screening decreases with increasing lFor a given n: s < p < d < fEffective nuclear charge: ZeffEffective nuclear charge, Zeff: the net positive charge attracting an electron in an atom.An approximation to this net charge is Zeff(effective nuclear charge) = Z(actual nuclear charge) - Zcore(core electrons)The core electrons are in subshell between the electron in question and the nucleus. The core electrons are said to “shield” the outer electrons from the full force of the nucleusSince the energy of an orbital depends on Zeff, in a many electron atom, for a given value of n, the energy of a orbital increases with increasing value of l.7Electron shielding (screening) of the nuclear charge by other electronsWhy is the energy of a 3s orbital lower than than of a 3p orbital? Why is the energy of a 3p orbital lower than the energy of a 3d orbital?A qualitative explanation is found in the concept of effective nuclear charge “seen” by an electron8Effective charge, Zeff, seen by valence electrons*:Rule: Zeff increases going across a period ot the table*Note x-axis is incorrect. What should it be?9Let’s take a look at some experimental data:The ionization energy (IE) of an atom is the minimum energy required to remove an electron from a gaseous atom.X(g) X+(g) + e- The first ionization energy IE1 is the energy required to remove the first electron from the atom. The second ionization energy IE2, is the energy required to remove the second electron from the +1 positive ion of the atom and so on.Ionization energies (ionization potentials):10Periodic trends ionization energies of the representative elements: What are the correlations across and down?11How do we obtain ionization energies?Photoelectron spectroscopy is an important technique that provides the energies of electrons in different orbitals and provides overwhelming evidence for the existence of shells and subshells.Photoelectron spectroscopy is the photoelectric effect explained by Einstein applied to gases:A photon hhits an electron and ejects it from the atom; part of the energy of the photon goes into overcoming the attraction of the electron for the nucleus (the ionization energy, IE) and the remainder appears as kinetic energy: h=  + (1/2)mv2Or:  = h- (1/2)mv2 (total photon energy - KE)12Photoelectron spectroscopy: the photoelectric effect for ejecting electrons from gaseous atoms.1s 2s 2pt, IE = h - (1/2)mv2Energy diagram for Ne: 1s22s22p61s2I onizedNe atom2s22p6-1.6 Ry-3.6 Ry-64 Ry0 Ry13Experimental data and theoretical ideasQuestion: Explain the “two slopes” for the ionization energies of carbon.Slope 2Slope 1146C 1s22s22p26C+5 1s12s02p06C+4 1s22s02p06C+3 1s22s12p06C+2 1s22s22p06C+1 1s22s22p1It takes more and more energy to remove an electron from an increasingly positively charged atom.The first smaller slope is due to removal of n = 2 electrons, the second larger slope is due to removal of n = 1 electrons.2s1s2p15Looking for trends: Ionization energies in tabular formLots of data but hard to see trends16Periodic trends of the first ionization energies of the representative elements mapped on the periodic table. IE IncresaseIE DecreaseAre correlations more apparent? What are they?17Looking for trends. Ionization energies as a graph: Periodic trendsBig drop after noble gases:ns2np6 ns2np6(n +1)s118Ionization energies of the main group elements in topographical relief form: family relationships.Why is the IE of H so much larger than the IE of Li? Why are the IEs of the alkali metals so similar?Why do noble gases have the highest IE?19First and Second ionization energies in graphical form Why is the IE of N greater than that of C or O?N OC20IE13Li [He]2s () 4Be [He]2s2 ()5B [He]2s22p1 () 6C [He]2s22p2 ()7N [He]2s22p3 () 8O [He]2s22p4 () 9F [He]2s22p5 () 10Ne [He]2s22p6 ()11Na [Ne]3s1 Using electron configurations to explain Ionization EnergiesRemoval of an electron from a neutral atom: IE1En = -(Zef2/n2)En = -(Zef2) if n is fixed(across a period)En = -(1/n2) if Zef is fixed(down a column)Zeff increases21IE2 (removal from E+)3Li+[He]+4Be+ [He] 2s1 ()5B+ [He] 2s2 ()6C+ [He] 2s22p2 ()7N+ [He] 2s22p3 () 8O+ [He] 2s22p4 () 9F+ [He] 2s22p5 () 10Ne+ [He] 2s22p6 ()11Na+ [Ne]+Using electron configurations to explain Ionization EnergiesRemoval of the second