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Atomic Structure

Atomic Structure. Nuclear and Electronic Organization. Atoms. Notion dates from ca 400 BCE - Democritus Notion lay dormat 2200 years until early 1800’s - John Dalton. John Dalton. 1766-1844. Dalton’s Theory. Explained Conservation of Mass in chemical and physical changes

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Atomic Structure

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  1. Atomic Structure Nuclear and Electronic Organization

  2. Atoms • Notion dates from ca 400 BCE - Democritus • Notion lay dormat 2200 years until early 1800’s - John Dalton

  3. John Dalton 1766-1844

  4. Dalton’s Theory • Explained Conservation of Mass in chemical and physical changes • Accounted for differences between elements and compounds • Accounted for constant composition of compound substances. Water, eg, always 88.9% oxygen and 11.1% hydrogen

  5. Atoms • Incredibly small • Sub-microscopic • Yet much is understood, measurable of sub-atomic structure

  6. Two Major Zones or Regions • Nucleus • Dense, central core • Almost all of the atomic mass • only about 1-trillionth of the space or volume • Extranuclear, or electron, region • Most of the atomic volume • Almost none of the atom’s mass • Almost “empty space”

  7. Nucleus Extra-nuclear (electron) region Atom

  8. Electrons negative (-1) negligible mass (0.0 amu) outside nucleus Protons positive (+1) part of nucleus 1.0 amu Neutrons neutral part of nucleus 1.0 amu Three Sub-atomic Particles

  9. Atoms of Various Elements • Same no. of p+ for given element • equal to atomic number • equal to e- no. for neutral atoms • Neutron nos. may vary for atoms of same element • isotopes • average no. of neutrons determinable from atomic mass info

  10. 17 Cl 35.453 No. of protons Average mass, average total of p+ & n

  11. No. of protons Average no neutrons  18.5 17 Cl 35.453

  12. Cl-35or Cl-37or 35 37 Cl Cl 17 17 17 p+ 18n 17 p+ 20n Two Isotopes for Cl Mass = 37 amu ca 25% of isotopes Mass = 35 amu ca 75% of isotopes Average mass = 35.453

  13. No. of protons Average no neutrons  12.3053 12 Mg 24.3050

  14. Mg-26or Mg-24or Mg-25or 25 24 26 Mg Mg Mg 12 12 12 12 p+ 12n 12 p+ 14n 12 p+ 13n Three Isotopes for Mg Mass = 26 amu ca 11% of isotopes Mass = 25 amu ca 10% of isotopes Mass = 24 amu ca 79% of isotopes Average mass = 24.3050

  15. Electron Organization • Outside nucleus • Grouped in increasing levels of energy • Lowest-energy e- nearest nucleus • Limited no. e- at each level (more at higher levels) • Transitions of e- between levels absorb or release energy

  16. Energy Levels Levels approach a continuum for most atoms beyond then 10th level. 1 2 3 4 5 6 7 8, 9, 10, etc

  17. Electron Transitions Energy absorbed • • 1 2 3 4 5 6 7 8, 9, 10, etc

  18. Electron Transitions • • Energy released 1 2 3 4 5 6 7 8, 9, 10, etc

  19. Electron Transitions • Give rise to absorption and emission spectra • Only certain colors (or wavelengths) observed for given element • Spectrum (color set) for each element can be used to identify element in unknown sample

  20. Spectra

  21. Spectra

  22. Spectra

  23. Maximum Occupancy of Energy Levels • Level 1 -- 2 e- • Level 2 -- 8 e- • Level 3 -- 18 e- • Level 4 -- 32 e- • … • Level n -- 2 x n2 e- • Actual occupancy  32 e-

  24. Energy Levels 18e- 32e- 8e- Levels approach a continuum for most atoms beyond then 10th level. 2e- 1 2 3 4 5 6 7 8, 9, 10, etc

  25. Li 2, 1 Same as: 3 Lithium 2e- 1e-

  26. N 2, 5 Same as: 7 Nitrogen 2e- 5e-

  27. Same as: Ne 2, 8 10 Neon 2e- 8e- Largest atom for which all electrons exist only at main levels 1 and 2.

  28. Same as: Na 2, 8, 1 11 Sodium 1e- 2e- 8e- Smallest atom for which an electron must exist at main level 3.

  29. Same as: Ar 2, 8, 8 18 Argon 8e- 2e- 8e- Largest atom for which all electrons can exist within first three main levels.

  30. Atoms with At. No. > 18 Although level #3 can have 18 total electrons, level #4 must contain next 2 electrons; additional electrons after the 20th go back to level #3 (up to 18, maximum). 8e- 2e- “Filling order”: Level 1 - 2e- Level 2 - 8e- Level 3 - 8e- Level 4 - 2e- Level 3 - up to 18 total 8e-

  31. Same as: K 2, 8, 8, 1 19 Potassium 1e- 8e- 2e- 8e- Smallest atom for which energy level 4 must be occupied.

  32. Fe 2, 8, 14, 2 26 Iron 2e- 14e- Same as: 2e- 8e- Filling: 1st 18e-: 2,8,8 Next 2e-: 2,8,8,2 Last 6e-: 2, 8, 14, 2

  33. Same as: Zn 2, 8, 18, 2 30 Zinc 2e- 18e- 2e- 8e- Filling: 1st 18e-: 2,8,8 Next 2e-: 2,8,8,2 Last 10e-: 2, 8, 18, 2

  34. Good News! • Our requirements for electron configurations are - • limited to 30 e-, total (Zn) • involve main levels only (no s, p, d, f “orbital” or “subshell” configurations required) • Much of electron configuration determinable from Periodic Table

  35. Periodic Table of the Elements 1 H 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac 104 105 106 107 108 109 110 111 112 VIII I V III IV VI VII II 1 2 3 4 5 6 7

  36. “Periodic” Properties • Properties of the elements that change periodically (cyclically) as the atomic number increases. • Examples • Chemical reactivity • Atomic size (diameter, radius, eg.) • Ionization energy • Electronegativity • Metallic/non-metallic character

  37. Chemical Reactivity • Properties are similar for elements in same family or vertical group. • Group I: Li, Na, K, etc • Group II: Be, Mg, Ca, etc • Group VII: F, Cl, Br, I, etc • Similar kinds of reactions • Similar kinds of compounds

  38. Requires warm water; sluggish Similar Reactions Vigorous in cool water; may explode Consider Group I: Li, Na, K, Rb, Cs Explosion likely; very dangerous Li + H2O  explosive gas, alkaline solution Na + H2O  explosive gas, alkaline solution K + H2O  explosive gas, alkaline solution Rb + H2O  explosive gas, alkaline solution Cs + H2O  explosive gas, alkaline solution Run! Call 911 Our condolences.

  39. Similar Compounds Again, consider Group I: Li, Na, K, Rb, Cs “Sulfides”: Li2S, Na2S, K2S, Rb2S, Cs2S “Chlorides”: LiCl, NaCl, KCl, RbCl, CsCl “Phosphates”: Li3PO4,Na3PO4, K3PO4, Rb3PO4, etc

  40. Similar Compounds For Group II: Be, Mg, Ca, Sr, Ba “Sulfides”: BeS, MgS, CaS, SrS, BaS “Chlorides”: BeCl2, MgCl2, CaCl2, SrCl2, BaCl2 “Phosphates”: Be3(PO4)2, Mg3(PO4)2, Ca3(PO4)2, etc

  41. 1 H 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac 104 105 106 107 108 109 110 111 112 Atomic Size small LARGE

  42. Li 2, 1 3 Same as: 2e- 1e- Na 2, 8, 1 11 1e- Same as: 2e- 8e- K 2, 8, 8,1 1e- 19 8e- Same as: 2e- 8e- Atomic Diameter Increases going down a “family” or group. More energy levels occupied.

  43. 3+ 6+ 9+ 2e- 2e- 2e- 4e- 1e- 7e- Same as: Same as: Same as: Li 2, 1 C 2, 4 F 2, 7 3 6 9 Atomic Diameter Diameter shrinks going rightward across a period.

  44. Atomic Diameter Li 2, 1 3 Same as: 2e- 1e- 3+ Approx +1 at outer level Na 2, 8, 1 11 1e- Same as: 2e- 11+ 8e- Approx +1 at outer level 8e- K 2, 8, 8,1 19 Same as: 1e- 19+ 2e- 8e- Approx +1 at outer level “Shielding by “core” electrons keeps effective charge at outer level about the same within a family or group.

  45. Ionization Energy (Potential) • Minimum energy required to remove electron from gaseous atom: X(g) + I.E.  e- + X+(g) • I.E. is high for atoms which hold very tightly to their outer electrons • non-metals have high I.E.’s; metals, low • highest for smallest atoms. Ion -- at atom (or group of atoms) with net charge

  46. 1 H 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac 104 105 106 107 108 109 110 111 112 Ionization Energy Small size LARGE I.E. LARGE SIZE small I.E.

  47. Electronegativity • Tendency of atom to hold to its electron when sharing electrons with neighboring atom. • Generally, follow same trends as I.E. • Important for bonding polarity (next unit of study)

  48. Metallic Character 1 H 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne Non-metals 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe Metals 55 Cs 56 Ba 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac 104 Rf 105 Db 106 Sg 107 Bh 108 Hs 109 Mt 110 111 112

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