Ch 7 The Structure of Atoms and Periodic Trends 7 1 The Pauli Exclusion Principle States that no more than 2 electrons can occupy the same orbital and if there are 2 electrons in the same orbital they must have opposite spins Or stated another way No 2 electrons in an atom may have identical sets of 4 quantum numbers Shells n then subshells l then orbitals ml Quick trick Table 7 1 p 302 Clicker Q How many electrons fit into the Clicker Q How many electrons fit into the 7 2 Atomic Subshell Energies and Electron Assignments Quick trick Fig 7 1a p 303 Order of Subshell Energies and Assignments Aufbau principle German means building up Electrons in an atom are assigned to shells and subshells in order of increasingly higher energy Total energy of the atom is as low as possible Quick trick again good video of atomic orbitals long video http www youtube com watch v yKgSSPkgldk feature related Orbital energy diagram Effective Nuclear Charge Z Net charge experienced by a particular electron in a multi electron atom resulting from a balance of the attractive force of the nucleus and the repulsive forces of other electrons The outermost electrons in an atom experience attractive forces to the atom s nucleus as well as repulsive forces from the other electrons in the atom Z increases across a period owing to incomplete screening by inner electrons Figure 7 2 Effective nuclear charge Z Fig 7 2b p 304 7 3 Electron Configurations of Atoms Electron Configurations of the Main Group Elements Hydrogen Lithium Li and other elements of Group 1A Always ends in s1 Noble gas notation The electrons included in the noble gas notation are referred to as the core electrons Valence electrons the outermost electrons highest n number Beryllium Be and Other Elements of Group 2A Always ends in s2 Clicker Q How many valence e does have Boron B and Other Elements of Group 3A Always ends in s2 p1 Carbon C and Other Elements of Group 4A Always ends in s2 p2 Clicker Q How many valence e does have Nitrogen N and Oxygen O and other Elements of Groups 5A and 6A 5A ends in 6A ends in Clicker Q Fluorine F and Neon Ne and Elements of Groups 7A and 8A Clicker Q How many valence e does have Electron configuration and orbital box diagram Hund s rule the most stable arrangement of electrons is that with the maximum number of unpaired electrons all with the same spin direction Electrons occupy all the orbitals of a given subshell singly before pairing begins These unpaired electrons have parallel spins N Cl P Ar What element has the following e configuration 1s2 2s2 2p6 3s2 3p6 4s1 Ar 4s2 3d10 4p3 Kr 5s2 4d10 5p6 6s2 4f14 5d10 6p4 Ar 4s2 3d5 Clicker Q Give electron configuration of Electron Configurations of the Transition Elements Transition elements fill d orbitals Inner transition elements fill f orbitals 7 4 Electron Configurations of Ions Electrons are removed from the highest n level and maximum l level Do e config and orbital diagram Isoelectronic same of electrons with what other elements ions Na Al3 Fe3 V3 O 2 F Zn2 has what electron configuration Use noble gas configuration so Ar A monoatomic ion has a 2 charge and has the following electron configuration Kr What is the element 7 5 Atomic Properties and Periodic Trends Similarities in properties of the elements are the result of similar valence shell electron configurations Atomic Size Atomic radii describe the relative sizes of atoms Atomic radii increase within a column going from the top to the bottom of the periodic table Atomic radii decrease within a row going from left to right on the periodic table Atomic Radii of Elements Decreases Atomic Size Size decreases across a period owing to increase in Z read page 312 Each added electron feels a greater and greater charge Effective nuclear charge Z attractive effect of an additional proton in the nucleus outweighs the repulsive effect of an additional electron Large Small Increase in Z The reason the atomic radii decrease across a period is due to shielding or screening effect Effective nuclear charge Z experienced by an electron is less than the actual nuclear charge Z The inner electrons block the nuclear charge s effect on the outer electrons Clicker Q Put in order from smallest to largest no spaces between Ionization Energy Ionization Energy IE is the energy required to remove an electron from an atom in the gas phase Because energy must be supplied to overcome the attraction of the nuclear charge ionization energies are always positive Mg g 738 kJ Mg g e First Ionization Energies of the main group elements in the first four periods Ionization Energy Periodic trends for Ionization Energy 1 IE2 IE1 It always takes more energy to remove a second electron from an ion than from a neutral atom 2 IE1 generally increases moving from 1A elements to 8A elements Important exceptions at Be Mg N P etc due to filled and half filled subshells 3 IE1 generally decreases moving down a family IE1 for Li IE1 for Na etc 34 Ionization Energy Second ionization energy IE2 The amount of energy required to remove the second electron from a gaseous 1 ion Symbolically ion energy ion2 eMg 1451 kJ mol Mg2 e 35 Ionization Energy Group and element IA Na IIA Mg IIIA Al IE1 kJ mol IE2 kJ mol IE3 kJ mol IE4 kJ mol 496 738 578 4562 1451 1817 6912 7733 2745 9540 10 550 11 580 37 Ionization Energy The reason Na forms Na and not Na2 is that the energy difference between IE1 and IE2 is so large Requires more than 9 times more energy to remove the second electron than the first one The same trend is persistent throughout the series Thus Mg forms Mg2 and not Mg3 Al forms Al3 38 Ionization Energy Group and element IE1 kJ mol IE2 kJ mol IE3 kJ mol IE4 kJ mol IE5 kJ mol IE6 kJ mol Group Group Group Group Group 496 738 578 418 423 4562 1451 1817 889 1258 6912 7733 2745 1269 2157 1757 2698 10000 3578 9540 10 550 11 580 35006 40 Ionization Energy Clicker Q what charge ion would be expected for an element that has these ionization energies 1 2 3 1 2 3 Hint look for the biggest jump in energy happeen That jump is where you are removing a core electron which means all the previously removed electrons are valence electrons ANSWER 1 IE1 kJ mol 1680 IE2 kJ mol 3370 IE3 kJ mol 6050 IE4 kJ mol 8410 IE5 kJ mol 11020 IE6 kJ mol 15160 IE7 kJ mol 17870 IE8 kJ mol 92040 41 Electron Attachment Enthalpy and Electron Affinity The electron attachment enthalpy EAH is defined as the enthalpy change occurring when a gaseous atom adds an electron forming a gaseous anion Cl g e