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APChem- Chapter 7 Lecture- Periodic Trends
- 1. Development of PeriodicTable Elements in the same group generally have similar chemical properties. Properties are not identical, however.
- 2. Development of PeriodicTable Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.
- 3. Development of PeriodicTable 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.
- 4.
- 5.
- 6. The atomic numberdepends on the number of protons in the nucleus, while the atomic weight depends (mainly) on the number of both protons and neutrons in the nucleus.
- 7. Periodic Trends Inthis chapter, we will rationalize observed trends in Sizes of atoms and ions. Ionization energy. Electron affinity.
- 8. Effective Nuclear ChargeIn 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.
- 9. The attraction ofan electron to the nucleus depends on The charge of the nucleus The distance the electron is from the nucleus. In large atoms, the electrons in outer shells do not experience the full charge of the nucleus because inner shells of electrons “shield” them from the nucleus.
- 10. Effective Nuclear ChargeThe 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.
- 11.
- 12.
- 13. The 2 p electron of a Ne atom.
- 14. 2 s orbital 2 p orbital 3 s orbital 3 p orbital 3 d orbital In an germanium atom, which electron will experience the greatest effective nuclear charge? An electron in a…
- 15. 2 s orbital 2 p orbital 3 s orbital 3 p orbital 3 d orbital In an germanium atom, which electron will experience the greatest effective nuclear charge? An electron in a…
- 16. The effective nuclearcharge experienced by 3 p electrons in phosphorus is +2 +3 +5 +7
- 17. +2 +3 +5+7 Correct Answer: The effective nuclear charge is given by the equation: Z eff = Z S where Z represents number of protons in the nucleus and S represents the average number of electrons between the nucleus and the electron in question. Here: Z eff = 15 10 = +5
- 18. Sizes of AtomsIt is difficult to define atomic radii for single atoms because the outside of the electron cloud is ambiguous.
- 19. Sizes of AtomsThe non-bonding atomic radius is defined as one-half of the distance between two atoms when they collide.
- 20. Sizes of AtomsThe bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.
- 21. Sizes of AtomsAdding two bonding radii together gives a useful estimate of bond length.
- 22. Sizes of AtomsBonding atomic radius tends to… … decrease from left to right across a row due to increasing Z eff . … increase from top to bottom of column due to increasing value of n
- 23.
- 24.
- 25. Order the followingaccording to increasing atomic radius. Ge < Si < Se < Cl Se < Si < Ge < Cl Si < Cl < Ge < Se Cl < Si < Se < Ge Si < Ge < Se < Cl Ge Si Se Cl
- 26. Order the followingaccording to increasing atomic radius. Ge < Si < Se < Cl Se < Si < Ge < Cl Si < Cl < Ge < Se Cl < Si < Se < Ge Si < Ge < Se < Cl Ge Si Se Cl
- 27. Based on atomicradii, which of the following bonds would be expected to be the shortest? H H H F F F Cl Cl
- 28. Correct Answer: Theshortest bonding atomic radius belongs to the H atom, so an H 2 molecule will have the shortest H X (where X is any atom) bond distance. H H H F F F Cl Cl
- 29. Sizes of IonsIonic size depends upon: Nuclear charge. Number of electrons. Orbitals in which electrons reside.
- 30. Sizes of IonsCations are smaller than their parent atoms. The outermost electron is removed and repulsions are reduced.
- 31. Sizes of IonsAnions are larger than their parent atoms. Electrons are added and repulsions are increased.
- 32. Sizes of IonsIons increase in size as you go down a column. Due to increasing value of n .
- 33. Sizes of IonsIn an isoelectronic series , ions have the same number of electrons. Ionic size decreases with an increasing nuclear charge.
- 34.
- 35. Order the followingaccording to increasing atomic/ionic radius. C < Li + < O 2 - < N 3 - N 3 - < O 2 - < C < Li + Li + < C < N 3 - < O 2 - Li + < C < N 3 - < O 2 - Li + < C < O 2 - < N 3 - N 3 - Li + C O 2 -
- 36. Order the followingaccording to increasing atomic/ionic radius. C < Li + < O 2 - < N 3 - N 3 - < O 2 - < C < Li + Li + < C < N 3 - < O 2 - Li + < C < N 3 - < O 2 - Li + < C < O 2 - < N 3 - N 3 - Li + C O 2 -
- 37. Which is larger: Na + or Na? Na + Na
- 38. Na + NaCorrect Answer: Both have the same number of protons, but Na with one more electron will be larger.
- 39. Which is larger: Cl or Cl? Cl Cl
- 40. Cl ClCorrect Answer: Both have the same number of protons, but Cl − with one more electron will be larger.
- 41. Lecture 7b- Sections7.4 - 7.5
- 42. Ionization Energy Amountof energy required to remove an electron from the ground state of a gaseous atom or ion. First ionization energy is that energy required to remove first electron. Second ionization energy is that energy required to remove second electron, etc.
- 43.
- 44.
- 45. Ionization Energy Itrequires more energy to remove each successive electron. When all valence electrons have been removed, the ionization energy shows a HUGE increase.
- 46.
- 47.
- 48. I 2 for the carbon atom is greater.
- 49. Trends in FirstIonization 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.
- 50. Trends in FirstIonization 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. And the electron’s distance from the nucleus decreases.
- 51. Trends in FirstIonization Energies However, there are two apparent discontinuities in this trend.
- 52. Trends in FirstIonization Energies The first occurs between Groups IIA and IIIA. Electron removed from p -orbital rather than s -orbital Electron farther from nucleus Small amount of repulsion by s electrons.
- 53. Trends in FirstIonization Energies The second occurs between Groups VA and VIA. Electron removed comes from doubly occupied orbital. Repulsion from other electron in orbital helps in its removal.
- 54.
- 55. Which will havethe highest ionization energy? C N O Al Si
- 56. Which will havethe highest ionization energy? C N O Al Si
- 57. Which will bethe largest? I 1 of Na I 2 of Na I 1 of Mg I 2 of Mg I 3 of Mg I = ionization energy
- 58. Which will bethe largest? I 1 of Na I 2 of Na I 1 of Mg I 2 of Mg I 3 of Mg I = ionization energy
- 59.
- 60. They have thesame electron configuration: [Ar]3d 3 .
- 61. Electron Affinity Energychange accompanying addition of electron to gaseous atom: Cl + e − Cl −
- 62.
- 63.
- 64. They are equalin magnitude and opposite in sign.
- 65. Trends in ElectronAffinity In general, electron affinity becomes more exothermic as you go from left to right across a row.
- 66. Trends in ElectronAffinity There are again, however, two discontinuities in this trend.
- 67. Trends in ElectronAffinity The first occurs between Groups IA and IIA. Added electron must go in p -orbital, not s -orbital. Electron is farther from nucleus and feels repulsion from s -electrons.
- 68. Trends in ElectronAffinity The second occurs between Groups 4A and 5A. Added electron must go in an occupied p -orbital.
- 69.
- 70. Based on periodictrends, which of the following elements is expected to have the largest (i.e., most negative) electron affinity? K Na Si S
- 71. Correct Answer: Shas most negative electron affinity in this list. K Na Si S
- 72. Lecture 7c- Sections7.6 - 7.8
- 73. Properties of Metal,Nonmetals, and Metalloids
- 74. Metals versus NonmetalsTable 7.3 on page 277 Differences between metals and nonmetals tend to revolve around these properties.
- 75. Metals versus NonmetalsMetals tend to form cations. (Low I.E.) Nonmetals tend to form anions. ( exo E.A.)
- 76. Metals Tend tobe lustrous, malleable, ductile, and good conductors of heat and electricity.
- 77. Metals Compounds formedbetween metals and nonmetals tend to be ionic. Metal oxides tend to be basic.
- 78. Metal oxide +water metal hydroxide MgO (s) + H 2 O (l) Mg(OH) 2 (aq) but only if it dissolves a bit in water Metal oxide (a.k.a. base anhydride) reactions Metal oxide + acid water + salt MgO (s) + HCl (aq) MgCl 2 (aq) + H 2 O (l)
- 79. Nonmetals Dull, brittlesubstances that are poor conductors of heat and electricity. Tend to gain electrons in reactions with metals to acquire noble gas configuration.
- 80. Nonmetals Substances containingonly nonmetals are molecular compounds. Most nonmetal oxides are acidic.
- 81. nonmetal oxide +water acid SO 3 (g) + H 2 O (l) H 2 SO 4 (aq) nonmetal oxide (acid anhydride) reactions nonmetal oxide + base water + salt CO 2 (g) + 2NaOH (aq) Na 2 CO 3 (aq) + H 2 O (l)
- 82. Metalloids Have somecharacteristics of metals, some of nonmetals. For instance, silicon looks shiny, but is brittle and fairly poor conductor.
- 83.
- 84. Alkali Metals Soft,metallic solids. Name comes from Arabic word for ashes.
- 85. Alkali Metals Foundonly as compounds in nature. Have low densities and melting points. Also have low ionization energies.
- 86. Alkali Metals Theirreactions with water are famously exothermic. 2M (s) + H 2 O (l) 2MOH (aq) + H 2 (g)
- 87. Alkali Metals Alkalimetals (except Li) react with oxygen to form peroxides. K, Rb, and Cs also form superoxides: K + O 2 KO 2 Produce bright colors when placed in flame.
- 88. Alkaline Earth MetalsHave higher densities and melting points than alkali metals. Have low ionization energies, but not as low as alkali metals.
- 89. Alkaline Earth MetalsBe does not react with water, Mg reacts only with steam, but others react readily with water. Reactivity tends to increase down the group. Mg (s) + 2H 2 O (g) Mg(OH) 2 (aq) + H 2 (g)
- 90. Hydrogen Hydrogen isa nonmetal. It has a high ionization energy because its single electron experiences no nuclear shielding When it does lose it’s electron it isn’t really an atom anymore. It is a proton.
- 91. Group 6A Oxygen,sulfur, and selenium are nonmetals. Tellurium is a metalloid. The radioactive polonium is a metal.
- 92. Oxygen Two allotropes:O 2 O 3 , ozone Three anions: O 2 − , oxide O 2 2 − , peroxide O 2 1 − , superoxide Tends to take electrons from other elements (oxidation)
- 93. Sulfur Weaker oxidizingagent than oxygen. Most stable allotrope is S 8 , a ringed molecule.
- 94. Group VIIA: Halogens Prototypical nonmetals Name comes from the Greek halos and gennao : “salt formers”
- 95. Group VIIA: Halogens Large, negative electron affinities Therefore, tend to oxidize other elements easily React directly with metals to form metal halides Chlorine added to water supplies to serve as disinfectant
- 96. Group VIIIA: Noble Gases Astronomical ionization energies Positive electron affinities Therefore, relatively unreactive Monatomic gases
- 97. 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.