1. © 2012 Pearson Education, Inc. Chapter 7 Periodic Properties of the Elements Subhash C Goel South GA State College Douglas, GA 31533

2. Copyright © Cengage Learning. All rights reserved.8 | 2 You learned how the organization of the periodic table can be explained by the periodicity of the ground-state configurations of the elements. Now we will look at various aspects of the periodicity of the elements.

3. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Development of Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be grouped.

4. © 2012 Pearson Education, Inc. Periodic Table Both Scientists noted: Similar chemical and physical properties recur periodically when elements are arranged in order of increasing atomic weight. Mendeleev got more credit for advancing his ideas and stimulating new work.

5. Copyright © Cengage Learning. All rights reserved.8 | 5 Mendeleev’s periodic table generally organized elements by increasing atomic mass and with similar properties in columns. In some places, there were missing elements whose properties he predicted. When gallium, scandium, and germanium were isolated and characterized, their properties were almost identical to those predicted by Mendeleev for eka-aluminum, eka-boron, and eka-silicon, respectively.

6. Copyright © Cengage Learning. All rights reserved.8 | 6 Periodic law states that when the elements are arranged by atomic number, their physical and chemical properties vary periodically. We will look in more detail at three periodic properties: atomic radius, ionization energy, and electron affinity.

7. Copyright © Cengage Learning. All rights reserved.8 | 7 Effective Nuclear Charge Effective nuclear charge is the positive charge that an electron experiences from the nucleus. It is equal to the nuclear charge, but is reduced by shielding or screening from any intervening electron distribution (inner shell electrons).

8. Copyright © Cengage Learning. All rights reserved.8 | 8 Effective nuclear charge increases across a period. Because the shell number (n) is the same across a period, each successive atom experiences a stronger nuclear charge. As a result, the atomic size decreases across a period.

9. Periodic Properties of the Elements © 2012 Pearson Education, Inc. What Is the Size of an Atom? The bonding atomic radius is defined as one-half of the distance between covalently bonded nuclei.

10. © 2012 Pearson Education, Inc.

11. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Sizes of Atoms The 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 the increasing value of n).

12. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.1 Bond Lengths in a Molecule Solve C—S bond length = bonding atomic radius of C + bonding atomic radius of S = 0.77Å + 1.02Å = 1.79Å C—H bond length = 0.77Å + 0.37Å = 1.14Å S—H bond length = 1.02Å = 0.37Å = 1.39Å Solution Natural gas used in home heating and cooking is odorless. Because natural gas leaks pose the danger of explosion or suffocation, various smelly substances are added to the gas to allow detection of a leak. One such substance is methyl mercaptan, CH 3 SH. Use Figure 7.6 to predict the lengths of the C—S, C—H, and S—H bonds in this molecule.

13. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Sizes of Ions Ionic size depends upon –The nuclear charge. –The number of electrons. –The orbitals in which electrons reside.

14. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Sizes of Ions Cations are smaller than their parent atoms: The outermost electron is removed and repulsions between electrons are reduced. Anions are larger than their parent atoms” Electrons are added and repulsions between electrons are increased. Ions increase in size as you go down a column: This increase in size is due to the increasing value of n.

15. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.3 Atomic and Ionic Radii Cations are smaller than their parent atoms, and so Ca 2+ Ca 2 + > Mg 2+. Solution Arrange Mg 2+, Ca 2+, and Ca in order of decreasing radius..

16. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Sizes of Ions In an isoelectronic series, ions have the same number of electrons. Ionic size decreases with an increasing nuclear charge.

17. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.4 Ionic Radii in an Isoelectronic Series Arrange the ions K +, Cl –, Ca 2 +, and S 2– in order of decreasing size. Solution This is an isoelectronic series, with all ions having 18 electrons. In such a series, size decreases as nuclear charge (atomic number) increases. The atomic numbers of the ions are S 16, Cl 17, K 19, Ca 20. Thus, the ions decrease in size in the order S 2– > Cl – > K + > Ca 2+.

18. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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 the first electron. –The second ionization energy is that energy required to remove the second electron, etc.

19. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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.

20. © 2012 Pearson Education, Inc.

21. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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. Generally, as one goes across a row, it gets harder to remove an electron. –As you go from left to right, Z eff increases.

22. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Trends in First Ionization Energies However, there are two apparent discontinuities in this trend. The first occurs between Groups IIA and IIIA (Be and B) In this case the electron is removed from a p orbital rather than an s orbital. –The electron removed is farther from the nucleus. –There is also a small amount of repulsion by the s electrons. The second discontinuity occurs between Groups VA and VIA (N and O). –The electron removed comes from a doubly occupied orbital. –Repulsion from the other electron in the orbital aids in its removal.

23. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Electronic Configuration of Ions Li (1s 2 2s 1 )→Li+ (1s 2 ) + e - Fe([Ar]3d 6 4s 2 )→Fe 2+ ([Ar]3d 6 ) + 2e - Fe 2+ ([Ar]3d 6 )→Fe 3+ ([Ar]3d 5 ) + e - Sn([Kr]4d 10 5s 2 5p 2 → Sn 2+ ([Kr]4d 10 5s 2 ) Sn 2+ ([Kr]4d 10 5s 2 )→Sn 4+ ([Kr]4d 10 ) F(1s 2 2s 2 2p 5 ) + e - → F - (1s 2 2s 2 2p 6 )

24. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.7 Electron Configurations of Ions (a) Calcium (atomic number 20) has the electron configuration [Ar]4s 2. To form a 2+ ion, the two outer electrons must be removed, giving an ion that is isoelectronic with Ar: Ca 2 :[Ar] (b) Cobalt (atomic number 27) has the electron configuration [Ar]3d 7 4s 2. To form a 3+ ion, three electrons must be removed. As discussed in the text, the 4s electrons are removed before the 3d electrons. Co 3+ :[Ar]3d 6 (c) Sulfur (atomic number 16) has the electron configuration [Ne]3s 2 3p 4. To form a 2– ion, two electrons must be added. There is room for two additional electrons in the 3p orbitals. S 2– :[Ne]3s 2 3p 6 = [Ar] Solution Write the electron configuration for (a) Ca 2+, (b) Co 3+, and (c) S 2–.

25. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Electron Affinity Electron affinity is the energy change accompanying the addition of an electron to a gaseous atom: Cl + e −  Cl −

26. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Trends in Electron Affinity

27. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Trends in Electron Affinity In general, electron affinity becomes more exothermic as you go from left to right across a row. There are again, however, two discontinuities in this trend.

28. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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 the nucleus and feels repulsion from the s electrons. The second discontinuity occurs between Groups IVA and VA. –Group VA has no empty orbitals. –The extra electron must go into an already occupied orbital, creating repulsion.

29. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Properties of Metal, Nonmetals, and Metalloids

30. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Metals versus Nonmetals Differences between metals and nonmetals tend to revolve around these properties.

31. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Metals versus Nonmetals Metals tend to form cations. Nonmetals tend to form anions.

32. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Metals Compounds formed between metals and nonmetals tend to be ionic. Metal oxides tend to be basic. Metals have low IE

33. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.8 Metal Oxides (a) Because scandium oxide is the oxide of a metal, we expect it to be an ionic solid. Indeed it is, with the very high melting point of 2485ºC. (b) In compounds, scandium has a 3+ charge, Sc 3+, and the oxide ion is O 2–. Consequently, the formula of scandium oxide is Sc 2 O 3. Metal oxides tend to be basic and, therefore, to react with acids to form a salt plus water. In this case the salt is scandium nitrate, Sc(NO 3 ) 3 : Sc 2 O 3 (s) + 6 HNO 3 (aq) → 2 Sc(NO 3 ) 3 (aq) + 3 H 2 O(l) Solution (a) Would you expect scandium oxide to be a solid, liquid, or gas at room temperature? (b) Write the balanced chemical equation for the reaction of scandium oxide with nitric acid.

34. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Nonmetals Nonmetals 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.

35. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Nonmetals Substances containing only nonmetals are molecular compounds. Most nonmetal oxides are acidic.

36. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.9 Nonmetal Oxides Write the balanced chemical equation for the reaction of solid selenium dioxide, SeO2(s), with (a) water, (b) aqueous sodium hydroxide. (a) The reaction between selenium dioxide and water is like that between carbon dioxide and water (Equation 7.13): SeO 2 (s) + H 2 O(l) → H 2 SeO 3 (aq) (It does not matter that SeO 2 is a solid and CO 2 is a gas under ambient conditions; the point is that both are water-soluble nonmetal oxides.) (b) The reaction with sodium hydroxide is like the reaction in Equation 7.15: SeO 2 (s) + 2 NaOH(aq) → Na 2 SeO 3 (aq) + H 2 O(l) Solution

37. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Metalloids Metalloids have some characteristics of metals and some of nonmetals. For instance, silicon looks shiny, but is brittle and a fairly poor conductor.

38. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Group Trends

39. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Alkali Metals Alkali metals are soft, metallic solids. The name comes from the Arabic word for ashes.

40. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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.

41. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Alkali Metals Their reactions with water are famously exothermic.

42. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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.

43. © 2012 Pearson Education, Inc. Chemistry, The Central Science, 12th Edition Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward Sample Exercise 7.10 Reactions of an Alkali Metal Write a balanced equation for the reaction of cesium metal with (a) Cl 2 (g), (b) H 2 O(l), (c) H 2 (g). (a)The reaction between Cs and Cl 2 is a simple combination reaction between a metal and a nonmetal, forming the ionic compound CsCl: 2 Cs(s) + Cl 2 (g) → 2 CsCl(s) (b)2Cs(s) + 2 H 2 O(l) → 2 CsOH(aq) + H 2 (g) (c)2 Cs(s) + H 2 (g) → 2 CsH(s) All three reactions are redox reactions where cesium forms a Cs + ion. The Cl –, OH –, and H – are all ions, which means the products have 1:1 stoichiometry with Cs +. Solution

44. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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.

45. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Alkaline Earth Metals Beryllium does not react with water, and magnesium reacts only with steam, but the other alkaline earth metals react readily with water. Reactivity tends to increase as you go down the group.

46. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Group 6A Oxygen, sulfur, and selenium are nonmetals. Tellurium is a metalloid. The radioactive polonium is a metal.

47. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Sulfur Sulfur is a weaker oxidizer than oxygen. The most stable allotrope is S 8, a ringed molecule.

48. Periodic Properties of the Elements © 2012 Pearson Education, Inc. Group VIIA: Halogens The halogens are prototypical nonmetals. The name comes from the Greek words halos and gennao: “salt formers.”

49. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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.

50. Periodic Properties of the Elements © 2012 Pearson Education, Inc. 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.