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NIS – CHEMISTRY

NIS – CHEMISTRY. Lecture 25 Electron Configuration Ozgur Unal. Electron Configuration. How do large number of people start seating after they get on a bus ?. Ground State Electron Configuration. Electrons occupy the orbitals in a similar way with the people on a bus .

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NIS – CHEMISTRY

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  1. NIS – CHEMISTRY Lecture 25 ElectronConfiguration OzgurUnal

  2. ElectronConfiguration How do largenumber of people start seatingaftertheyget on a bus?

  3. GroundStateElectronConfiguration Electronsoccupytheorbitals in a similarwaywiththepeople on a bus. Inordertoshowthis, weuseelectronconfiguration. Thearrangement of electrons in an atom is calledtheatom’selectronconfiguration. • Low-energyatomsaremorestablethanhighenergyatoms. • Electrons in an atom tendtoassumethearrangementthatgivesthe atom thelowestenergypossible. • Themoststable, lowestenergyarrangement of electrons is calledthegroundstateelectronconfiguration.

  4. GroundStateElectronConfiguration Thereare 3 rulesthat define howelectrons can be arranged in an atom’sorbitals. AufbauPrinciple ThePauliExclusionPrinciple Hund’sRule • TheAufbauPrinciple: • Theaufbauprinciplestatesthateachelectronoccupiesthelowestenergyorbitalavailable. • Aufbaudiagramshowsthesequence of atomicorbitalsfromlowestenergytohighestenergy • CheckTabe 5.3

  5. ThePauliExclusionPrinciple Electrons in orbitals can be representedbyarrows in boxes. Eachelectron has an associatedspin. An electron can spin in onlyone of twodirections. Arrowuprepresents an electronspinning in onedirection, arrowdownrepresentonespinning in theotherdirection. An emptyboxrepresents an orbitalwithoutelectrons. A boxwithtwoarrowsrepresents a filledorbital

  6. ThePauliExclusionPrinciple ThePauliExclusionPrinciplestatesthat a maximum of twoelectrons can occupy a singleatomicorbitalandthesetwoelectronsmusthaveoppositespins. WolfganPauli (1900-1958) Themaximumnumber of electronsrelatedtoeachprincipalenergylevel is 2n2.

  7. Hund’sRule Hund’sRulestatesthatsingleelectronswiththesamespinmustocupyeachequal-energyorbitalbeforeadditionalelectronswithoppositespins can occupythesameorbitals.

  8. ElectronArrangement Electrons in orbitals can be representedbyarrows in boxes. Eachbox is labeledwiththeprincipalquantumnumberandsublevelassociatedwiththeorbital. Example: Carbon atom has 6 electrons. Initsgroundstatethereare 2 electrons in 1s, 2 electrons in 2s and 2 electrons in 2p.

  9. ElectronConfigurationNotation Theelectronconfigurationnotationdesignatestheprincipalenergyleveland a energysublevelassociatedwitheach of theatom’sorbitalsandincldues a superscriptrepresentingthenumber of electrons in theorbital. Example: Carbon in itsgroundstate 1s2 2s2 2p2 CheckTable 5.4 • Noble-gasnotation: • This is a method of representingelectronconfigurationsusingnoblegases. • Noblegasesaretheelements in thelastcolumnoftheperiodictable. • Example:Aluminum ---- > [Ne] 3s2 3p1

  10. ElectronConfigurationNotation

  11. ExceptionstoPredictedConfigurations Therearesomeexceptionstotheelectronconfigurationsforsomeelements. UptoandincludingVanadium, we can usetheaufbaudiagramtowrite correctground stateelectron configurations. ForCr, Cuand someother elements, the configurations is slightlydifferent.

  12. NIS – CHEMISTRY Lecture 26 Valence Electrons OzgurUnal

  13. Valence Electrons Valence electronsaredefined as electrons in theatom’soutermostorbitals. Example: Sulfur has 16 electrons, 6 of whichare at theoutermostorbitals (3s and 3p). Sulfur has 6 valence electrons. Example: Cesium has 55 electrons, 1 of which is in theoutermostorbital (6s). Cs has 1 valence electron.

  14. Electron-dotStructure AmericanchemistG.N. Lewisdevised a method, calledelectron-dorstructure, toshow an atoms valence electrons. An atom’selectron-dotstructureconsists of theelement’ssymbol, whichrepresentsthenucleusandinner-levelelectrons, surroundedbythe dotsrepresentingall of the atom’s valence electrons.

  15. Electron-dotStructure Example: Sometoothpastescontainstannousfluoride, a compound of tin andfluorine. What is tin’selectrondotstructure? • Example: An atom of an element has total 13 electrons. What is the element, andhowmanyelectronsareshown in itselectron-dotstructure?

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