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UNIT 2

UNIT 2. Atoms, Ions, Electronic Structure, and Periodic Properties of Atoms and Ions. Effective Nuclear Charge: Z eff. The effective nuclear charge Z eff experienced by the valence electrons is helpful in explaining the periodic trends of the properties of the elements.

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UNIT 2

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  1. UNIT 2 Atoms, Ions, Electronic Structure, and Periodic Properties of Atoms and Ions

  2. Effective Nuclear Charge: Zeff The effective nuclear charge Zeff experienced by the valence electrons is helpful in explaining the periodic trends of the properties of the elements. For the valence electrons, Zeff is approximated by taking the difference between the charge on the nucleus and the charge of the core electrons.

  3. Effective Nuclear Charge (Zeff) For the valence electrons, Zeff is approximated by taking the difference between the charge on the nucleus and the charge of the core electrons. Zeff (Mg) = 12 – 10 = +2 for the two 3s valence electrons.

  4. Periodic Trends – Size of Atoms e- configuration Zeff atomic radius Z Element (core notation) =(Z-core) (bonding) _____ _______ ________________ _______ _______________ 1 H 1s1 1-0 = +1 0.37Å 3 Li [He]2s13-2 = +1 1.34Å 11 Na [Ne]3s1 11-10 = +1 1.54Å 19 K [Ar]4s1 19-18 = +1 1.96Å 37 Rb [Kr]5s1 37-36 = +1 2.11Å 1 Å = 1 angstrom = 0.1 nm Atomic sizeincreasesdown a group.

  5. Periodic Trends – Size of Atoms e- configuration Zeff atomic radius Z Element (core notation) =(Z-core) (bonding) _____ _______ ________________ _______ _______________ 11 Na [Ne]3s1 11-10 = +1 1.54Å 12 Mg [Ne]3s2 12-10 = +2 1.30Å 13 Al [Ne]3s23p1 13-10 = +3 1.18Å 14 Si [Ne]3s23p2 14-10 = +4 1.11Å 15 P [Ne]3s23p3 15-10 = +5 1.06Å 16 S [Ne]3s23p4 16-10 = +6 1.02Å 17 Cl [Ne]3s23p5 17-10 = +7 0.99Å Atomic size generally decreases across a period due to the increasing Zeff experienced by the valence electrons (while n doesn’t change). Atomic size generally increases right to leftin a period.

  6. Periodic Trends – Size of Atoms

  7. Periodic Trends – Size of Atoms increasing size increasing size

  8. Periodic Trends – Size of Cations atomic radius ionic radius Element e- config (Å) ion e- config (Å) ________ ________ _______ ___ _________ ___________ Li [He]2s1 1.34 Li+ [He] 0.68 Na [Ne]3s11.54 Na+ [Ne] 0.97 K [Ar]4s1 1.96 K+ [Ar] 1.33 Rb [Kr]5s1 2.11 Rb+ [Kr] 1.47 1. The cation is ALWAYS SMALLER than its atom. 2. Otherwise, the trends in cation size are the same as atomic size. Ionic size increases down a group.

  9. Periodic Trends – Size of Anions atomic radius ionic radius Element e- config (Å) ion e- config (Å) ________ ________ _______ ___ _________ ___________ F [He]2s22p5 0.71 F- [Ne] 1.33 Cl [Ne]3s23p5 0.99 Cl- [Ar] 1.81 Br [Ar]3d104s24p5 1.14 Br- [Kr] 1.96 I [Kr]4d105s25p51.33 I- [Xe] 2.20 1. The anion is ALWAYS LARGER than its atom. 2. Otherwise, the trends in anion size are the same as atomic size. Ionic sizeincreasesdown a group.

  10. Periodic Trends – Size of Ions

  11. Periodic Trends – Size of Ions in an Isoelectronic Series atomic radius ionic radius ion e- config (Å) ion e- config (Å) ________ ________ _______ ___ _________ ___________ N3- 1s22s22p6 1.71 Na+ 1s22s22p6 0.97 O2- 1s22s22p6 1.40 Mg2+ 1s22s22p6 0.66 F- 1s22s22p6 1.33 Al3+ 1s22s22p6 0.51 Ions in anisoelectronic seriesall haveexactly the same electronic configuration. Ionic size in an isoelectronic seriesdecreaseswith increasing nuclear charge (Z).

  12. Periodic Trends – Ionization Energy Ionization energy (I.E.) is the energy needed to remove an electron from an atom in its gaseous state. Na (g)  Na+ (g) + e- e- configuration first ionization Z Element (core notation) energy (kJ/mol) _____ _______ ________________ ___________________ 1 H 1s1 1312 3 Li [He]2s1 520 11 Na [Ne]3s1 496 19 K [Ar]4s1 419 37 Rb [Kr]5s1 403 Ionization energy generally increases up a group.

  13. Periodic Trends – Ionization Energy Ionization energy (I.E.) is the energy needed to remove an electron from an atom in its gaseous state. Na (g)  Na+ (g) + e- e- configuration first ionization Z Element (core notation) energy (kJ/mol) _____ _______ ________________ _________________ 11 Na [Ne]3s1 496 12 Mg [Ne]3s2 738 13 Al [Ne]3s23p1 578 14 Si [Ne]3s23p2 786 15 P [Ne]3s23p3 1012 16 S [Ne]3s23p4 1000 17 Cl [Ne]3s23p5 1251 18 Ar [Ar] 1521 Ionization energy generally increases across a period.

  14. Periodic Trends – Ionization Energy

  15. Periodic Trends – Ionization Energy increasing I.E. increasing I.E.

  16. Periodic Trends – Electron Affinity Electron affinity (E.A.) is the energy released when an electron is added to a gaseous element. F (g) + e- F- (g) e- configuration electron affinity Z Element (core notation) (kJ/mol) _____ _______ ________________ _______________ 9 F [He]2s22p5 -328 17 Cl [Ne]3s23p5-349 35 Br [Ar]3d104s24p5 -325 53 I [Kr]4d105s25p5 -295 Negative energies denote large electron affinities. Electron affinity generally increases up a group.

  17. Periodic Trends – Electron Affinity Electron affinity (E.A.) is the energy released when an electron is added to a gaseous element. F (g) + e- F- (g) e- configuration electron affinity Z Element (core notation) energy (kJ/mol) _____ _______ ________________ _______________ 11 Na [Ne]3s1 -53 12 Mg [Ne]3s2 >0 13 Al [Ne]3s23p1-43 14 Si [Ne]3s23p2 -134 15 P [Ne]3s23p3-72 16 S [Ne]3s23p4 -200 17 Cl [Ne]3s23p5-349 18 Ar [Ar] >0 Negative energies denote large electron affinities. Electron affinity generally increases across a period.

  18. Periodic Trends – Electron Affinity increasing E.A. increasing E. A.

  19. Periodic Trends – Metallic Character • Metallic character is • luster • malleability • ductility • good conductivity • the tendency to form ionic oxides that are basic. • Metallic character is closely related to how easily electrons can be removed from an element. The lower the I.E. of an element, the higher its metallic character.

  20. Periodic Trends – Metallic Character increasing metallic character increasing metallic character

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