Chapter 1 — IntroductionCHEM 101CHEM 101Fall 2013Fall 2013Dr. Michael Stollenz7. Periodic Trends2•Electrons in an atom are arranged by•the Principal Quantum Number n→→→→ shells•the Angular Momentum Quantum Number l→→→→ subshells•the Magnetic Quantum Number ml→→→→ orbitals•the Electron Spin Quantum Number ms→ spin stateQuantum NumbersQuantum Numbers7. Periodic Trends7. Periodic Trends3•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.•Two electrons of the same atom cannot have the same set of four quantum numbers (n, l, ml, and ms).PauliPauliExclusion PrincipleExclusion Principle7. Periodic Trends7. Periodic Trends4•Example n = 1, l = 0:This shell has a single orbital (1s) to which 2 electrons can be assigned.•Example n = 2, l = 0, 1:2s orbital: 2 electrons3 × 2p orbitals: 6 electrons∑8 electronsPauliPauliExclusion PrincipleExclusion Principle7. Periodic Trends7. Periodic Trends5•Example n = 3, l = 0, 1, 2:3s orbital: 2 electrons3 × 3p orbitals: 6 electrons5 × 3d orbitals: 10 electrons∑18 electronsPauliPauliExclusion PrincipleExclusion Principle7. Periodic Trends7. Periodic Trends6•Example n = 4, l = 0, 1, 2, 3:4s orbital: 2 electrons3 × 4p orbitals: 6 electrons5 × 4d orbitals: 10 electrons7 × 4f orbitals: 14 electrons∑32 electrons→Maximum electrons possible for nth shell:2n2PauliPauliExclusion PrincipleExclusion Principle7. Periodic Trends7. Periodic TrendsChapter 1 — Introduction7•Degenerate orbitals are filled with electrons (with the same spin direction) until all are half-filled before pairing up of electrons can occur.•Example: The degenerate 2p orbitalsHundHund’’ssRuleRule7. Periodic Trends7. Periodic Trends2p↑↑↑↑↑↑↑↑↑↑↑↑8SubshellSubshellEnergy LevelsEnergy Levels7. Periodic Trends7. Periodic Trends•In a hydrogen atom (1 electron) the orbitals of a subshell are equal in energy (degenerate)1s2s3s4s2p3p3dEnergy9SubshellSubshellEnergy LevelsEnergy Levels7. Periodic Trends7. Periodic Trends•In a multielectron atom the energy levels of orbitals of a subshell follow the orderof increasing n + l.2s3s4s2p3p3dE = n + l3d: n + l = 3 + 2 = 54s: n + l = 4 + 0 = 41s: n + l = 1 + 0 = 12s: n + l = 2 + 0 = 22p: n + l = 2 + 1 = 33s: n + l = 3 + 0 = 33p: n + l = 3 + 1 = 410The The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic Trends11•Why do we have the certain subshell filling order (1s→2s→2p→3s→3p→4s→3d8)?•The reason is the effective nuclear charge Z*.The The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic Trends12•The reason is the effective nuclear charge Z*.•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 electrons.The The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic TrendsChapter 1 — Introduction137. Periodic Trends7. Periodic TrendsLi atom147. Periodic Trends7. Periodic TrendsLi atom•The 2s electron experiences a positive charge greater than +1 but much smaller than +3(+1.28 for Li).15•Z* is the charge “felt” by the electron (usually) in the highest occupied orbitaland is then expressed by Z* = Z – S(S= screening constant)•Z* increases across a period owing to incomplete screening by inner electrons.The The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic Trends16•The relative extent to which an outer electron penetrates inner orbitals is s>p>d>f.•Therefore the effective nuclear charge Z* experienced by electrons in a multielectronsystem is in the orderns>np>nd>nfThe The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic Trends17The The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic Trends18The The AufbauAufbauPrinciplePrinciple7. Periodic Trends7. Periodic TrendsChapter 1 — Introduction19•The electron configurations follow three principles:1) Aufbau Principle: Lower energy orbitals fill first.2) Hund’s Rule: Degenerate orbitals are filled with electrons (with the same spin direction) until all are half-filled before pairing up of electrons can occur. Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic Trends20•The electron configurations follow three principles:3) 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.•We then have the electron configuration of an atom which represents the total number of the electrons from the lowest to the highest shell.Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic Trends21Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic TrendsGroup 1AAtomic number = 33 total electronsspdf notation: 1s22s11s2s3s3p2p1s 2s 2p↑↑↑↑↑↑↑↑ ↑↑↑↑LithiumBox notation22Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic TrendsGroup 2AAtomic number = 44 total electronsspdf notation: 1s22s21s 2s 2p↑↑↑↑↑↑↑↑ ↑↑↑↑BerylliumBox notation↑↑↑↑1s2s3s3p2p237. Periodic Trends7. Periodic TrendsBeLispdf notations ns1and ns2: s-block elements24Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic TrendsGroup 3AAtomic number = 55 total electronsspdf notation:1s22s22p11s 2s 2p↑↑↑↑↑↑↑↑ ↑↑↑↑BoronBox notation↑↑↑↑↑↑↑↑1s2s3s3p2pChapter 1 — Introduction25Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic TrendsGroup 4AAtomic number = 66 total electronsspdf notation:1s22s22p21s 2s 2p↑↑↑↑↑↑↑↑ ↑↑↑↑CarbonBox notation↑↑↑↑↑↑↑↑↑↑↑↑1s2s3s3p2p26Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic TrendsGroup 5AAtomic number = 77 total electronsspdf notation:1s22s22p31s 2s 2p↑↑↑↑↑↑↑↑ ↑↑↑↑NitrogenBox notation↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑1s2s3s3p2p27Electron ConfigurationsElectron Configurations7. Periodic Trends7. Periodic TrendsGroup 6AAtomic number = 88 total electronsspdf notation:1s22s22p41s 2s 2p↑↑↑↑↑↑↑↑ ↑↑↑↑OxygenBox notation↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑1s2s3s3p2p28Electron ConfigurationsElectron