Chem 103, Section F0FUnit II - Quantum Theory and Atomic StructureLecture 8•More on the periodic table•Some characteristics of atoms that have more than 1 electron•The quantum mechanical model of the atom and the periodic tableLecture 8 - Electron Configuratioin•Reading in Silberberg-Chapter 8, Section 1 Development of the periodic table-Chapter 8, Section 2 Characteristics of many-electron atoms-Chapter 8, Section 3 The quantum-mechanical model and the periodic table2Lecture 8 - IntroductionThe periodic law gave rise to the periodic table•In the mid to late 1800’s scientists, such as Demtri Mendeleev, where looking for ways to organize their knowledge of the the properties of the known elements.-This led to the creation of the Periodic Table.•In this lecture we will see that the discoveries of the early 1900’s, which led to the quantum mechanical model for the structure of the atom allows us to see how the arrangement of the elements in the periodic table are intimately related to their electronic configurations.3Lecture 4 - The Atomic Theory Today4In the 19th century, investigators looked for ways to organize what was known about the various elements.Dmitri Mendeleev (1836-1907) created one of the most useful arrangements, in which the elements were arranged by mass.•In this arrangement, Mendeleev also grouped elements with similar physical and chemical properties.Lecture 8 - Periodic LawOne of the powerful aspect of Mendeleev’s periodic table was it ability to predict the physical and chemical properties of elements yet to be discovered.•For example:-Mendeleev was able to predict the properties of an element that he called “eka-silicon”-Later, when eka-silicon was isolated, it was found to have properties remarkably similar to those predicted by Mendeleev!This element is now called Germanium (Ge).5Lecture 8 - Periodic LawThe properties predicted for “eka-Silicon”6Lecture 8 - Periodic LawMendeleev’s table was arranged by the atomic mass of the elements.•There are some examples in Mendeleev’s table where the elements are out of order according to their masses.-This is because Mendeleev recognized that properties should trump masses in determining the arrangement of the elements in the periodic table.•Meendeleev’s placement of Telurium (Te), with a mass of 128, ahead of Iodine (I), with a mass of 127, is one example.7Lecture 8 - Periodic LawHenry Moseley (1887-1915)•In the early 1900’s, Henry Moseley discovered a way of determining the number of protons in an element by analyzing the X-rays emitted by an atom upon being bombarded by a beam of electrons.•This allowed the periodic chart to now be arranged by atomic number, which displays no issues with ordering.8Lecture 8 - Many-Electron AtomsSchrödinger’s quantum-mechanical model allows for the electronic configurations of atoms containing more than one electron to be approximated.The addition of more than 1 electron requires three considerations to be made:•The need for a forth quantum number, ms.•A limit on the number of electrons that can occupy a single orbital (the exclusion rule).•The existence of a more complex set of energy levels.9Lecture 8 - Many-Electron AtomsWhen a beam of hydrogen atoms passes through a strong magnetic field it splits into two beams.•This is due the 1 electron in hydrogen atoms having one of two possible “spins”.10Lecture 8 - Many-Electron AtomsIdentifying electrons in many-electron atoms requires four quantum numbers•n, l, ml•Plus a forth, ms, electron spin, which is a property of the the electron.11Lecture 8 - Many-Electron AtomsIdentifying electrons in many-electron atoms requires four quantum number•n, l, ml•Plus a forth, ms, electron spin, which is a property of the the electron12Lecture 8 - Many-Electron AtomsPauli exclusion principle: No two electrons in the same atom can have the same four quantum numbers.•Named for Wolfgang Pauli, who was awarded the 1945 Nobel Prize in physics for his contribution to our understanding of the structure of the atom.•This limits each orbital in an atom to containing only 2 electrons.-The two electrons must have opposite spins.13Wolfgang Pauli(1900-1958)Lecture 8 - Many-Electron AtomsEnergy level splitting.•Electrostatic interactions between electrons in atoms with more than one electron causes the energy levels to split into sublevels.•The electrostatic effects include:-The effect of nuclear charge (Z)-The effect of electron repulsions and shielding on orbital energy -The effect of orbital shape on orbital energy (penetration)14Lecture 8 - Many-Electron AtomsThe effect of nuclear charge (Z)•Higher nuclear charge lowers the energy of an energy level.15Comparing the 1s orbital of H and He+Lecture 8 - Many-Electron AtomsThe effect of electron repulsions and shielding on orbital energy •The electrons feel not only the attraction of the nucleus, but also the repulsion of the other electrons.16Electron repulsionLecture 8 - Many-Electron AtomsThe effect of electron repulsions and shielding on orbital energy •The electrons feel not only the attraction of the nucleus, but also the repulsion of the other electrons.•Shielding by inner elecrons greatly lowers the effective nuclear charge (Zeff).17Electron shieldingLecture 8 - Many-Electron AtomsThe effect of orbital shape on orbital energy (penetration)•The different orbitals, which are defined by the l quantum number, place the electrons at different distances from the nucleus,-The more stable orbitals are the ones that come closer to the nucleus.•Sublevel energies:-s < p < d < f18Orbital penetrationLecture 8 - Many-Electron AtomsMultiple electrons in the same atoms leads to•electron-electron repulsion•nuclear shielding•energy-level splittingThese effects lead to more energy levels that predicted by the Bohr model•These additional energy levels are observed in the atomic spectra of atoms with more than one electron.19Lecture 8 - Many-Electron Atoms20Energy-level splitting defines the order in which the electrons are filledfillingorderLecture 8 - Quantum Mechanical Model of the Periodic TableThe electron configuration for an atom is a list of the orbitals that each of the electrons in the atom occupies.•We will focus on the ground state configuration, which places all of the electrons in the orbitals with the lowest possible energies.This list is most easily constructed by•starting with a naked nucleus with the desired