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Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry , 2007 (John Wiley)      ISBN: 9 78047081 0866 . CHEM1002 [Part 2]. A/Prof Adam Bridgeman (Series 1) Dr Feike Dijkstra (Series 2) Weeks 8 – 13

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  1. Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille,Chemistry, 2007 (John Wiley)     ISBN: 9 78047081 0866

  2. CHEM1002 [Part 2] A/Prof Adam Bridgeman (Series 1) Dr FeikeDijkstra (Series 2) Weeks 8 – 13 Office Hours: Monday 2-3, Friday 1-2 Room: 543a e-mail:adam.bridgeman@sydney.edu.au e-mail:feike.dijkstra@sydney.edu.au

  3. Periodic Trends • Lecture 4: • Titrations • Lecture 5: • Periodic Trends • Oxides and Hydroxides • Strengths of Acids and Bases • Blackman, Chapter 4, Section 4.8-4.9

  4. Periodicity of Atomic Radii Cs Rb K Na Li Xe Ar Kr Ne He

  5. Periodicity of Atomic Radii • Across each period • Increase in nuclear charge Z • Increase in e-/e- repulsion • Electrons move very fast and can avoid each other • Increase in effective nuclear charge: Zeff • Zeff increases across period • Size decreases across period

  6. Periodicity of Atomic Radii • Increase in size down each group • Increase in principal quantum number, n • Increase in shell size • Electrons in inner shells shield charge • Core charge = number of protons – number of core electronsZeff (Li) ≈ 3 - 2 = 1 • Zeff (Na) ≈ 11 - 10 = 1 • Zeff (K) ≈ 19 - 18 = 1 • Elements in a group have similar properties

  7. Trends in Two Atomic Properties increases decreases decreases increases atomic size ionization energy • Trends in atomic properties are usually either similar to the trend in the atomic radii or the exact opposite • Diagonally related elements often have similar properties: diagonal relationship

  8. Ionic and Atomic Radii • Ionization decreases e-/e- repulsion • Zeff increases • Cations are smaller than the respective atom • e.g. Ba - 222 pm but Ba2+ 135 pm • Adding an electron increases e-/e- repulsion • Zeff decreases • Anions are larger than the respective atom • e.g. O - 73 pm but O2- 140 pm , F 72 pm but F- 133 pm • Anions are often much larger than cations • e.g. Ba2+ 135 pm (row 6) but O2- 140 pm (row 2)

  9. Electronegativity • Tendency of an atom to attract electrons towards itself in a molecule • increases with Zeff • decreases with atomic size increases decreases electronegavity

  10. The Pure Elements • Bonding ranges from metallic for metals (bottom left of the periodic table) to covalent for non-metals (top right), with semimetals (metalloids) lying between. tend to gain electrons to form anions tend to lose electrons to form cations

  11. Oxides and Hydroxides I • Metal oxides and hydroxides are basic • Metal oxides and hydroxides are ionic due to large difference in electronegativity (EN ) between O and metal • Metal oxides (e.g. Na2O, EN = 2.6) contain the O2- ion, which combines with H+ to form H2O: • Na2O(s) + H2O(l)  2OH-(aq) + 2 Na+(aq) • Metal hydroxides (e.g.NaOH) contain the OH- ion • OH- and (especially) O2- have high affinity for H+ ion

  12. Oxides and Hydroxides II • Non-metal oxides and ‘hydroxides’ are acidic • non-metals form covalent bonds to oxygen due to low electronegativity difference • they do not contain O2- or OH- • Non-metal oxides dissolve in OH- to form a salt + H2O: • e.g. CO2(g) + 2OH-(aq)  CO32-(aq) + H2O(l) • Non-metal hydroxo compounds (e.g. HNO3, H2SO4) react with OH- as follows: • e.g. X-O-H(aq) + OH-(aq) X-O-(aq) + H2O(l)

  13. Oxides and Hydroxides III • Semi-metal (metalloid) oxides and ‘hydroxides’ are amphoteric - they can act both as acids and bases) • electronegativity is intermediate between metal and non-metal • As a base: • Al2O3(s) + 6 HCl(aq)  Al2Cl6(aq) + 3 H2O(l) • As an acid: • Al2O3(s) + 2 OH-(aq) + 3 H2O(l)  2 Al(OH)4-(aq)

  14. Acid-Base Behaviour electronegativity increases

  15. Strongest acids lose their protons easily more polarised the H-X bond is, the stronger the acid the larger the X is, the weaker the bond, the stronger the acid the more X=O groups, the greater the acid strength Relative Strengths of Acids and Bases increasing electronegativity, increasing acidity increasing bond length, increasing acidity

  16. Practice Examples • 1. Rank the following series of atoms in order of increasingelectronegativity. • N O F P As • (a) N < O < F < P < As • (b) F < O < N < P < As • (c) As < P < N < O < F • (d) P < As < N < O < F • (e) F < N < O < As < P • 2. Arrange the following atoms in order of increasing atomic radius. • N F Si P • (a) F < N < P < Si • (b) N < F < P < Si • (c) N < F < Si < P • (d) F < N < Si < P • (e) P < Si < N < F 3. Rank H2O(l), H2S(aq) and HF(aq) in order of their Brønsted acid strengths. Explain your reasoning (2007-N-3)

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