IB Chemistry on Periodic Trends, Effective Nuclear Charge and Physical properties.

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IB Chemistry on Periodic Trends, Effective Nuclear Charge and Physical properties.

Transcript of IB Chemistry on Periodic Trends, Effective Nuclear Charge and Physical properties.

  • 1.Periodic Table of elements divided to Groups, Periods and BlocksPeriod- Horizontal row 7 periods/row Same number of shellGroups Vertical column Same number of valence electron Same number outmost electronsGroup 1Block different region in periodic table s, p, d, f blocks s block- elements with valence e in s sublevel p block elements with valence e in p sublevel18Periods 17Excellent site from periodic videos Click here to views block - s orbitals partially filld block d orbitals partially fillp block p orbital partially fillf block f orbital partially fill

2. s block elements s orbitals partially fill1H Hep block elements p orbital partially fill51s2 n = 2 period 2B[He] 2s2 2p161s12Periodic Table s, p d, f blocks elementsC[He] 2s2 2p27N[He] 2s2 2p33Li[He] 2s18O[He] 2s2 2p44Be[He] 2s29F[He] 2s2 2p511Na[Ne] 3s110Ne[He] 2s2 2p612Mg[Ne] 3s213Al[Ne] 3s2 3p114 20K Ca[Ne] 3s2 3p2[Ar]15P[Ne] 3s2 3p3[Ar]4s216S[Ne] 3s2 3p41719Si4s1CI[Ne] 3s2 3p518Ar[Ne] 3s2 3p6d block elements d orbitals partially fill transition elements21Sc[Ar] 4s2 3d122Ti[Ar] 4s2 3d223V[Ar] 4s2 3d1324Cr[Ar] 4s1 3d525Mn[Ar] 4s2 3d526Fe[Ar] 4s2 3d627Co[Ar] 4s2 3d728Ni[Ar] 4s2 3d829Cu[Ar] 4s1 3d1030Zn[Ar] 4s2 3d10f block elements f orbitals partially fillVideo on electron configurationClick here electron structureClick here video on s,p,d,f notationClick here video s,p,d,f blocks, 3. Periodicity Predicted pattern/trends in physical/chemical properties across period. Physical propertiesChemical propertiesPhysical change - without change in molecular composition. appearance change - composition remain unchanged.Element properties Atomic properties Color, texture, odor Density, hardness, ductility Brittleness, Malleability Melting /boiling point Solubility, polarity Ionization energyPeriodic Trends Across period 2/3 Down group 1/17Atomic/ionic radiiGp 1 period 2 period 3Ionization energy Atomic radii Ionic radii ElectronegativityMelting pointElectronegativityGp 17Chemical change diff composition from original substances - chemical bonds broken/ formed - new products formed 4. Why IE increases across the period? Why IE decreases down a group ?Ionization energy (IE) 1st Ionization energy Min energy to remove 1 mole e from 1 mole of element in gaseous state M(g) M+ (g) + e2nd Ionization energy Min energy to remove 1 mole e from 1 mole of +1 ion to form +2 ion M+(g) M2+ (g) + eIonization energyFactors affecting ionization energy12Distance from nucleus3Nuclear chargeelectron+3+4+5+6Effective Nuclear Charge (ENC)/(Zeff) Screening effect/shielding Effective nuclear charge (ENC)/(Zeff) (Zeff) = Nuclear charge (Z) shielding effect Net positive charge felt by valence electrons.Nuclear charge increaseDistance near to nucleus IE High Distance far away nucleus IE Low Nuclear charge high (more proton) IE High Nuclear charge low (less proton) IE Low +6Inner electron shield valence e from positive nuclear chargeDistance nearNuclear charge Higher electron/electron repulsionStrong electrostatic forces attraction bet nucleus and eStrong electrostatic forces attraction bet nucleus and eEasier valence e to leaveIE High IE High IE Low 5. IE drop from Be to B and N to OIonization Energy- Period 2Why IE increases across the period 2? IE increases across period 2 Nuclear charge increase Strong electrostatic forces attraction bet nucleus and e IE High LiBeBCNOFNe2p 2s 1s 1s2 2s11s2 2s21s2 2s2 2p11s2 2s2 2p2IE drop from Be to B1s2 2s2 2p31s2 2s2 2p4IE drop from N to OElectron in p sublevel of B further away from nucleus2 electrons in same p orbital - Greater e/e repulsionWeak electrostatic force attraction between nucleus and electronEasier to remove eIE - Low IE - Low period 21s2 2s2 2p51s2 2s2 2p6 6. IE drop from Mg to AI and P to SIonization Energy- Period 3Why IE increases across the period 3? IE increases across period 3 Nuclear charge increase Strong electrostatic forces attraction bet nucleus and e IE High NaMgAISiPSCIAr3p3s [Ne] 3s1[Ne] 3s2[Ne] 3s2 3p1[Ne] 3s2 3p2IE drop from Mg to AI[Ne] 3s2 3p3[Ne] 3s2 3p4IE drop from P to SElectron in p sublevel of AI further away from nucleus2 electrons in same p orbital - Greater e/e repulsionWeak electrostatic force attraction between nucleus and electronEasier to remove eIE - Low IE - Low Period 3[Ne] 3s2 3p5[Ne] 3s2 3p6 7. IE for Period 2 and 3Ionization Energy- Period 2 and 3Why IE period 3 lower than 2? Period 3 3 shells/energy levelPeriod 3Valence e further from nucleusHigh shielding effect more inner eWeaker electrostatic forces attraction bet nucleus and e IE Lower period 2 LiBeBCNOFNe2p 2s 1s 1s2 2s11s2 2s21s2 2s2 2p11s2 2s2 2p21s2 2s2 2p31s2 2s2 2p41s2 2s2 2p51s2 2s2 2p6Period 3 NaMgAISiPS[Ne] 3s2 3p1[Ne] 3s2 3p2[Ne] 3s2 3p3[Ne] 3s2 3p4CIAr3rd level3p 3s 2p 2s 1s [Ne] 3s1[Ne] 3s2[Ne] 3s2 3p5[Ne] 3s2 3p6 8. IE for Ne and ArIonization Energy- Period 2 and 3Why Ne and Ar have HIGH IE ? Full electron configuration, 2.8/2.8.8neon argonMost energetically stable structure Difficult to lose electronIE High period 2 LiBeBCNOFNe2p 2s 1s 1s2 2s11s2 2s21s2 2s2 2p11s2 2s2 2p21s2 2s2 2p31s2 2s2 2p41s2 2s2 2p51s2 2s2 2p6Period 3 NaMgAISiPS[Ne] 3s2 3p1[Ne] 3s2 3p2[Ne] 3s2 3p3[Ne] 3s2 3p4CIAr3p 3s 2p 2s 1s [Ne] 3s1[Ne] 3s2[Ne] 3s2 3p5[Ne] 3s2 3p6 9. Atomic Radius Distance between nucleus and outmost electrons.Atomic radius Atom not like a ball cant measure its radius directly Uncertain about position of electron uncertain of atomic radius Uncertain abt electron positionHow to measure atomic radius?Half the distance bet nuclei of two closest identical atoms. Atomic RadiusCovalent MoleculeNoble gas Monoatomic atomsDepend on type of bonding covalent or metallicMetallic elementsIonic compounds bond length bond length bond lengthCovalent Radius bond length of 2 atomVan Der Waals radius bond length of nuclei atoms not bonded together (noble gas)Click here video on atomic radiusMetallic radius bond length bet nuclei of neighbouring metal ionsClick here video on atomic radiusIonic radius Measure indirectly using internucleus distanceClick here video on atomic radius 10. Effective Nuclear Charge (ENC)/(Zeff) Screening effect/shielding Effective nuclear charge (ENC)/(Zeff) (Zeff) = Nuclear charge (Z) shielding effect Net positive charge felt by valence electrons.Effective nuclear chargeEffective nuclear charge magnesium (2.8.2) net +2 10 inner electron shield 12+ protons Valence electron feel a net (12-10 = +2)Calculate Z(eff) and atomic radius for Li Effective nuclear charge, (Zeff) = +212Calculate Z(eff) for LiFormula ionization energyFcentripetal FcoulombLithium (2.1) Z2 IE 1312 2 n 2nd energy level n=2 Z2 521 1312 2 2 Z eff 1.26 1st IE Li = 521kJ/mol 2 inner electron shield 3+ protonsCalculate atomic radius Li using Z(eff)Rmv 2 kqZ 2 r R 2 mh kqZ m2 2 R 2 R h2 R m 2 kqZR 168pmh h p mv h v m vh mR2nd energy level n=2n2 2 2R Rm = mass electron -9.1 x 10-31 h = plank constant 6.626 x 10-34 k = coulomb constant 9.0 x 109 q = charge electron 1.6 x 10-19 Z = effective nuclear charge - +1.26Valence electron felt a net (3-2) = +1Z(eff) = +1.26 NOT +1 (calculation shown above) Click here video ENC LiClick here video calculating radius Li 11. Atomic Radius (Covalent radius)Atomic Radius- Period 2/3Why atomic radius decrease across period 2/3 Atomic radius decrease across period 2/3 Effective Nuclear charge increase Strong electrostatic forces attraction bet nucleus and eSize decrease Gp 17Li +3Be +4C +6N +7F +9O +8Effective Nuclear charge increase period 2Na +11period 3B +5Mg +12AI +13Si +14P +15S +16CI +17Effective Nuclear charge increase Why atomic radius increase down Gp 17?Screening/shielding effect increase Inner shell electrons electron electron repulsion increase Number shell increase Valence e further away from nucleusAtomic radius High 12. Positive Ions (+)Atomic and Ionic Radius- Period 2/3Ionic radii Positive ion (+) smallerNegative Ions (-)Ionic radii Negative ion (-) biggerDecrease in number of shells loss of electronIncrease in number of shells gain of electronLess electron electron repulsionIncrease electron electron repulsionSize decrease Size increase Comparison bet atomic/ionic radiiComparison bet atomic/ionic radiiIonic radii Ionic radii Atomic radii Atomic radiiNaMgAI2.8.12.8.22.8.3Na+2.8Mg2+2.8AI3+2.8Atomic radii- 3 shellsIonic radii - 2 shellsS2.8.6S2-2.8.8Atomic radii CI2.8.7CI-2.8.8- 3 shellsIonic radii- 2 shells 13. Electronegativity Electronegativity (EN) Tendency of atom to attract/pull shared/bonding electron to itself EN value higher pull/attract electron higher (EN value from 0.7 4) Shared electron cloud closer to O EN highestEN lowest Electronegativity EN increase up a Group EN increase across a PeriodSizeFactors affecting EN value Size of atom/distance small size/distance stronger attraction for electron Nuclear charge higher nuclear charge stronger attraction for electronGp 17 EN decrease down gp 17FSize increase Nuclear chargeCIAttraction electron decrease EN increase across period 2Li +3EN lower Be +4B +5C +6N +7O +8BrF +9Period 2 I EN increase across period 2Nuclear charge increase Strong attraction for electron EN increase 14. Melting point across Period 2/3 Melting point down Gp 1/17Melting Point Temp when solid turn to liquid (temp remain constant) Energy absorb to overcome forces attraction bet moleculePeriod 2/3Melting PointGp 1Gp 17Factors affecting melting pointType of bonding/forcesStructure Metallic/Non Metallic structureCovalent structureSimple molecular structureIonic structureMetallic BondingMelting point across Period 2 and 3Giant molecular structureperiod 2 C period 3BSiBe MgLiNa N O F NeAI P SCovalent BondingCIIonic Bonding 15. Melting point for metallic/non metallicMelting point across Period 2Melting PointCperiod 2B Be Li N O F NeLiBeBCNOFNem/p (/C)180128023003730-210-218-220-249structuremetallicmetallicGiant covalentGiant covalentSimple molecularSimple molecularS