Slide 1Development of Periodic TableDevelopment of Periodic TableDevelopment of Periodic TablePeriodic TrendsNuclear Charge (Z)Effective Nuclear Charge (Zeff)Effective Nuclear Charge, (Zeff)Sample ProblemPeriod Trends1. Atomic Radius SizeAtomic Size: Main GroupClicker: 7.1Atomic Size: Main GroupAtomic Size: Main GroupClicker: 7.2Atomic Size: Main GroupClicker: 7.32. Ionic (ION) Size2. Ionic (ION) SizeClicker: 7.63. Ionization Energy (IE)Ionization Energy (IE)Ionization Energy (IE)IE IrregularitiesClicker 7.7:Alkali Metals when added to water react violently4. Electron Affinity (EA)Electron Affinity (EA)Electron Affinity (EA)Clicker: 7.8Trend SummaryChange in Lecture Material1Periodic Trends of the ElementsChapter 7Chemistry the Central Scienceby: Brown, Lemay, Bursten, Murphy & WoodwardPresented by: Dr. Stacey GuldeDevelopment ofPeriodic TableMendeleev (Russian) & Meyer (German) 1869: independently published almost identical classifications of the elementsNoted many physical and chemical properties of the elements when arranged by increasing atomic weight•NOTE: Atomic #s were unknown at this time2Development ofPeriodic TableMendeleev given credit b/c insisted that elements w/similar characteristics be listed in same column, thus leaving blanks for undiscovered elementsPredicted placement & properties of Ga & Ge•Called them: eka-aluminum & eka-silicon, respectively–“eka” = below3Development ofPeriodic TableMoseley (1913): studied x-ray emissions of elements, found that x-ray frequencies increased w/atomic weight Assigned each freq. a whole number & called it: atomic number (# protons in nucleus)New system clarified some problems of MendeleevEx: Argon (Ar) Potassium (K)4Atomic weight:39.9 39.1Atomic #:18 19(out of order on PT)(in order on PT)5Periodic TrendsMany physical and chemical behaviors of an element are based on its electron configurationPeriodic trends – recurring patterns w/in a group (column) or period (row)Controlled by: placement of valence electrons & their attraction to their nucleusNuclear Charge(Z)Nuclear Charge, (Z) – attractive pull of protons (in nucleus) on an electronCoulomb’s law: •Attraction increases as: charge (Q) increases •Attraction decreases as: electron distance (d) increasesA high nuclear charge results in a strongnucleus–electron attraction 6  221dQQkZ Effective Nuclear Charge (Zef)When many electrons are present, each electron “feels”:1. the attractive pull of the nucleus (Z)2. the repulsion of the other electronsNot all electrons feel these forces equally!The core electrons prior to an electron of interest shields/screens (S) it from the nucleusEffective Nuclear Charge, (Zef)Effective Nuclear Charge, Zef - the lowering of what the electron of interest actually feels from the nucleus due to shieldingMore core electrons results in greater shieldingand a weaker nucleusActuallyfelt#Protons#COREelectronsShieldingElectronsZefSZZeffSample ProblemCalculate Zef for the valence electron in Na.9= 111s2 2s2 2p6 3s1- 10Zef = 1ProtonsCore e-s-SZZeffPeriod TrendsWe will investigate 4 types of trends, that we will be able to predict by looking at element positions on the periodic table1. Atomic radius size2. Ion radius size3. Ionization Energy (IE)4. Electron Affinity (EA)101. Atomic Radius SizeRemember: atoms represented by electrons whose position are know w/90% probabilityAtomic size – is an estimateBonding atomic radius – distance b/t identical nuclei & then divided in half•Can be used to determine radius of other atoms11199pmClClBondCClBond177pm100pm77pm~100pmAtomic Size: Main GroupA. Going DOWN, size increasesWhy?12Clicker: 7.113When going down a column, where do valence electrons go?Atomic Size: Main GroupA. Going DOWN: size increasesWhy?Electrons are placed farther from the nucleus (into larger energy, n, levels) thus atoms get biggerZef decreases due to increased shielding•More core electrons–Li has 2 core electrons–Cs has 54 core electrons14Atomic Size: Main GroupB. Going L to R: size decreasesWhy?15Clicker: 7.216When going across a row (LR), where do valence electrons go?Atomic Size: Main GroupB. Going L to R: size decreasesWhy?Electrons placed in same energy (n) levelsShielding (S) ineffective•Core electrons constant, causing Zef to increase–Li, 1s2 2s1: Zef = 3 – 2 = 1–Be, 1s2 2s2: Zef = 4 – 2 = 2–B, 1s2 2s2 2p1: Zef = 5 – 2 = 3The larger the Zef the stronger the “feel” of the nucleus•Thus, valence electrons are pulled in tighter17SZZeffClicker: 7.3Which atom will have the larger radius?Ca P182. Ionic (ION) SizeA. Cations – get smallerLose valence electrons•Less repulsionRemaining e-s pulled tighter to nucleus•Zef increasesEx: •Na = 1.54Å Na+ = 0.95Å•Mg = 1.30Å Mg+2 = 0.65Å•Al = 1.18Å Al+3 = 0.50ÅIonic radius – size of cation or anion (1st seen in Chap 6)2. Ionic (ION) SizeB. Anions – get largerGain valence electrons•More repulsionRemaining e-s spread out•Zef decreasesEx: •O = 0.73Å O2- = 1.40Å•F = 0.72Å F- = 1.36ÅC. Note: Column & row trend still applya) Top to bottom: Increaseb) Left to right: DecreaseClicker: 7.6Which of the following is the largest?21S2-S O2-3. Ionization Energy(IE)Ionization Energy (IE) – completely removes 1 mole of electrons from 1 mol of gaseous atoms or ionsRequires energy to overcome electron-nucleus attraction, IE always a positive valueThe larger (more positive) the IE, the harder to remove electronsAlways remove the outermost electronRemoval of 1st electron (IE1)Removal of 2nd electron (IE2))(gatom01IE)(gion12IEIE  egion )( egion )(223Ionization Energy(IE)Why is it harder to remove additional electrons?Pulling electrons from progressively more positive ions•Remaining electrons are attracted more to the nucleusZef gets largerNot smooth transition, large jumps exits, why?Removal of an inner (core) electron12IEIE Ionization Energy (IE)A. Moving Left to Right IE increasesAtoms get smaller, electrons held more tightly, thus harder to remove•Zef increasesB. Moving Top to Bottom IE decreasesAtoms get larger, electrons held less tightly, thus easier to remove•Zef decreases24IE IrregularitiesGroup 3 < Group 2: Greater than expected shielding