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AP Chemistry Chapter 7 Outline
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AP Chemistry Chapter 7 Outline

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  • 1. Chapter 7 Periodic Properties of the Elements Chemistry, The Central Science , 11th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten John D. Bookstaver St. Charles Community College Cottleville, MO
  • 2. Development of Periodic Table
    • Elements in the same group generally have similar chemical properties.
    • Physical properties are not necessarily similar, however.
  • 3. Development of Periodic Table
    • Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.
  • 4. Development of Periodic Table
    • Mendeleev, for instance, predicted the discovery of germanium (which he called eka-silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.
  • 5. Periodic Trends
    • In this chapter, we will rationalize observed trends in
      • Sizes of atoms and ions.
      • Ionization energy.
      • Electron affinity.
  • 6. Effective Nuclear Charge
    • In a many-electron atom, electrons are both attracted to the nucleus and repelled by other electrons.
    • The nuclear charge that an electron experiences depends on both factors.
  • 7. Effective Nuclear Charge
    • The effective nuclear charge, Z eff , is found this way:
    • Z eff = Z − S
    • where Z is the atomic number and S is a screening constant, usually close to the number of inner electrons.
  • 8. What Is the Size of an Atom?
    • The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.
  • 9. Sizes of Atoms
    • Bonding atomic radius tends to…
      • … decrease from left to right across a row
        • (due to increasing Z eff ).
      • … increase from top to bottom of a column
        • (due to increasing value of n ) .
  • 10. Sizes of Ions
    • Ionic size depends upon:
      • The nuclear charge.
      • The number of electrons.
      • The orbitals in which electrons reside.
  • 11. Sizes of Ions
    • Cations are smaller than their parent atoms.
      • The outermost electron is removed and repulsions between electrons are reduced.
  • 12. Sizes of Ions
    • Anions are larger than their parent atoms.
      • Electrons are added and repulsions between electrons are increased.
  • 13. Sizes of Ions
    • Ions increase in size as you go down a column.
      • This is due to increasing value of n .
  • 14. Sizes of Ions
    • In an isoelectronic series , ions have the same number of electrons.
    • Ionic size decreases with an increasing nuclear charge.
  • 15. Ionization Energy
    • The ionization energy is the amount of energy required to remove an electron from the ground state of a gaseous atom or ion.
      • The first ionization energy is that energy required to remove first electron.
      • The second ionization energy is that energy required to remove second electron, etc.
  • 16. Ionization Energy
    • It requires more energy to remove each successive electron.
    • When all valence electrons have been removed, the ionization energy takes a quantum leap.
  • 17. Trends in First Ionization Energies
    • As one goes down a column, less energy is required to remove the first electron.
      • For atoms in the same group, Z eff is essentially the same, but the valence electrons are farther from the nucleus.
  • 18. Trends in First Ionization Energies
    • Generally, as one goes across a row, it gets harder to remove an electron.
      • As you go from left to right, Z eff increases.
  • 19. Trends in First Ionization Energies
    • However, there are two apparent discontinuities in this trend.
  • 20. Trends in First Ionization Energies
    • The first occurs between Groups IIA and IIIA.
    • In this case the electron is removed from a p -orbital rather than an s -orbital.
      • The electron removed is farther from nucleus.
      • There is also a small amount of repulsion by the s electrons.
  • 21. Trends in First Ionization Energies
    • The second occurs between Groups VA and VIA.
      • The electron removed comes from doubly occupied orbital.
      • Repulsion from the other electron in the orbital aids in its removal.
  • 22. Electron Affinity
    • Electron affinity is the energy change accompanying the addition of an electron to a gaseous atom:
    • Cl + e −  Cl −
  • 23. Trends in Electron Affinity
    • In general, electron affinity becomes more exothermic as you go from left to right across a row.
  • 24. Trends in Electron Affinity
    • There are again, however, two discontinuities in this trend.
  • 25. Trends in Electron Affinity
    • The first occurs between Groups IA and IIA.
      • The added electron must go in a p -orbital, not an s -orbital.
      • The electron is farther from nucleus and feels repulsion from the s -electrons.
  • 26. Trends in Electron Affinity
    • The second occurs between Groups IVA and VA.
      • Group VA has no empty orbitals.
      • The extra electron must go into an already occupied orbital, creating repulsion.
  • 27. Properties of Metal, Nonmetals, and Metalloids
  • 28. Metals versus Nonmetals
    • Differences between metals and nonmetals tend to revolve around these properties.
  • 29. Metals versus Nonmetals
    • Metals tend to form cations.
    • Nonmetals tend to form anions.
  • 30. Metals
    • They tend to be lustrous, malleable, ductile, and good conductors of heat and electricity.
  • 31. Metals
    • Compounds formed between metals and nonmetals tend to be ionic.
    • Metal oxides tend to be basic.
  • 32. Nonmetals
    • These are dull, brittle substances that are poor conductors of heat and electricity.
    • They tend to gain electrons in reactions with metals to acquire a noble gas configuration.
  • 33. Nonmetals
    • Substances containing only nonmetals are molecular compounds.
    • Most nonmetal oxides are acidic.
  • 34. Metalloids
    • These have some characteristics of metals and some of nonmetals.
    • For instance, silicon looks shiny, but is brittle and fairly poor conductor.
  • 35. Group Trends
  • 36. Alkali Metals
    • Alkali metals are soft, metallic solids.
    • The name comes from the Arabic word for ashes.
  • 37. Alkali Metals
    • They are found only in compounds in nature, not in their elemental forms.
    • They have low densities and melting points.
    • They also have low ionization energies.
  • 38. Alkali Metals
    • Their reactions with water are famously exothermic.
  • 39. Alkali Metals
    • Alkali metals (except Li) react with oxygen to form peroxides.
    • K, Rb, and Cs also form superoxides:
    • K + O 2  KO 2
    • They produce bright colors when placed in a flame.
  • 40. Alkaline Earth Metals
    • Alkaline earth metals have higher densities and melting points than alkali metals.
    • Their ionization energies are low, but not as low as those of alkali metals.
  • 41. Alkaline Earth Metals
    • Beryllium does not react with water and magnesium reacts only with steam, but the others react readily with water.
    • Reactivity tends to increase as you go down the group.
  • 42. Group 6A
    • Oxygen, sulfur, and selenium are nonmetals.
    • Tellurium is a metalloid.
    • The radioactive polonium is a metal.
  • 43. Oxygen
    • There are two allotropes of oxygen:
      • O 2
      • O 3 , ozone
    • There can be three anions:
      • O 2 − , oxide
      • O 2 2 − , peroxide
      • O 2 1 − , superoxide
    • It tends to take electrons from other elements (oxidation).
  • 44. Sulfur
    • Sulfur is a weaker oxidizer than oxygen.
    • The most stable allotrope is S 8 , a ringed molecule.
  • 45. Group VIIA: Halogens
    • The halogens are prototypical nonmetals.
    • The name comes from the Greek words halos and gennao : “salt formers”.
  • 46. Group VIIA: Halogens
    • They have large, negative electron affinities.
      • Therefore, they tend to oxidize other elements easily.
    • They react directly with metals to form metal halides.
    • Chlorine is added to water supplies to serve as a disinfectant
  • 47. Group VIIIA: Noble Gases
    • The noble gases have astronomical ionization energies.
    • Their electron affinities are positive.
      • Therefore, they are relatively unreactive.
    • They are found as monatomic gases.
  • 48. Group VIIIA: Noble Gases
    • Xe forms three compounds:
      • XeF 2
      • XeF 4 (at right)
      • XeF 6
    • Kr forms only one stable compound:
      • KrF 2
    • The unstable HArF was synthesized in 2000.