CHEM 101 1st Edition Lecture 19Outline of Last Lecture I. The Schrödinger Wave EquationII. Electron SpinIII. Quantum NumbersIV. Pauli Exclusion PrincipleV. Hund’s RuleOutline of Current Lecture I. Subshell Energy LevelsII. Aufbau PrincipleIII. Electron ConfigurationCurrent Lecture- Subshell Energy Levelso In a multielectron atom the energy levels of orbitals of a subshell follow the order of the Aufbau Principle- ___ 8s___ ___ ___ ___ 7s 7p___ ___ ___ ___ ___ ___ ___ ___ ___ 6s 6p 6d___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 5s 5p 5d 5f___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 4s 4p 4d 4f___ ___ ___ ___ ___ ___ ___ ___ ___ 3s 3p 3d___ ___ ___ ___ 2s 2p___ 1so The reason is the effective nuclear charge Z*o Z* is the 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 electronso Z* is the charge “felt” by the electron (usually) in the highest occupied orbital and is then expressed by Z*=Z-S (S= screening constanto Z* increases across a period owing to incomplete screening by inner electrons- The Aufbau Principleo The relative extent to which an outer electron penetrates inner orbitals iss > p > d > fo Therefore the effective nuclear charge Z* experienced by electrons in a multielectron system is in the orderns > np > nd > nfo n= whatever number is in front of the letter (1-8)o l= 0-3, depending on the letter (s=0, p=1, d=2, f=3)- Electron Configurationso The electron configurations follow three principles: Aufbau Principle: lower energy orbitals fill first Hund’s Rule: degenerate orbitals are filled with electrons (with the samespin direction) until all are half-filled before pairing up of electron can occur. Pauli Exclusion Principle: no more than two electrons can occupy the same orbital, and, if there are two electrons in the same orbital, they must have opposite spins.o We then have the electron configuration of an atom which represents the total number of the electrons from the lowest to the highest shello Ex: Lithium Atomic number= 3 so 3 total electrons…__ 2s 1sTherefore, spdf notation: 1s^(2)2s^(1)o Ex: BerilliumAtomic number= 4 so 4 total electrons… 2s 1sTherefore, spdf notation: 1s^(2)2s^(2)o Ex: BoronAtomic number= 5 so 5 total electrons…__ ____ ____ 2s 2p 1sTherefore, spdf notation: 1s^(2) 2s^(2) 2p^(1)o Ex: CarbonAtomic number= 6 so 6 total electrons…__ __ ____ 2s 2p 1sTherefore, spdf notation: 1s^(2) 2s^(2) 2p^(2)o Ex: NitrogenAtomic number= 7 so 7 total electrons…__ __ __ 2s 2p 1sTherefore, spdf notation: 1s^(2) 2s^(2) 2p^(3)o Ex: OxygenAtomic number= 8 so 8 total electrons… __ __ 2s 2p 1sTherefore, spdf notation: 1s^(2) 2s^(2) 2p^(3)o Ex: FluorineAtomic number= 9 so 9 total electrons… __ 2s 2p 1sTherefore, spdf notation: 1s^(2) 2s^(2) 2p^(5)o Ex: NeonAtomic number= 9 so 9 total electrons…o 2s 2p 1sTherefore, spdf notation: 1s^(2) 2s^(2) 2p^(6)o The electron configuration of an element can be represented by the core electrons (noble gases notation) and the valence electrons: Ex: Silicon Atomic number= 14 so 14 total electrons…Noble Gas Notation: [Ne] 3s^(2)3p^(2)o 3d Transition Elements: 3d 4sCa [Ar]4s^(2) ___ ___ ___ ___ ___ Sc [Ar]3d^(1)4S^(2) __ ___ ___ ___ ___ Ti [Ar]3d^(2)4S^(2) _______ ___ ___ V [Ar]3d^(3)4S^(2) _________ ___ Cr [Ar]3d^(5)4S^(1) __________ Mn [Ar]3d^(5)4S^(2) __________ Fe [Ar]3d^(6)4S^(2) ________ Co [Ar]3d^(7)4S^(2) ______ Ni [Ar]3d^(8)4S^(2) ____ Cu [Ar]3d^(10)4S^(1) Zn [Ar]3d^(10)4S^(2) o Electron configurations are written by shell even though the electrons fill the orbitals following the Aufbau principle: Ex: Nickel:Electron Configuration by Aufbau principle:1s^(1)2s^(2)2p^(6)3s^(2)3p^(6)4s^(2)3d^(8)Electron Configuration by shell: 1s^(2)2s^(2)^(2)p^(6)3s^(2)3p^(6)3d^(8)4s^(2) Ex: Cerium: [Xe] 4f^(1)5d^(1)6s^(2) Ex: Uranium: [Rn] 5f^(3)6d^(1)7s^(2)- Atomic Radiio How can atomic radius be defined if we know that orbitals have no sharp boundaries? We consider the bond distance between atoms in elementso The half of the bond distance is called the covalent radius of the atom Cl:198 pm/2 = 99 pmo If the bond distance in a heteronuclear bond is known, then the covalent radius of another atom can be estimated:r (carbon)= 176pm-99pm = 77pmo Atomic Radii increases down the periodic table and from right to
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