1. LECTURE 6.2

2. LECTURE OUTLINE Weekly Reading Weekly Reading Prototype Practice Quiz 6: Feedback Prototype Practice Quiz 6: Feedback The Periodic Table The Periodic Table

3. CHAPTER XVII: THE METALLIC BOND Chapter 17 introduces the reader to the metallic bond: an oft-ignored "strong" bond, but one that is responsible for bonding in all metallic materials, virtually 75% of all known elements. It is shown that the "simple" nature of the metallic bond results in "close-packed" crystalline structures. The reader is introduced to the three major metallic structures: cubic close packed, hexagonal close packed, and body centered cubic. Chapter 17 also "hints" at the properties of metallic materials, in particular their melting points and their ductility. Chapter 17 introduces the reader to the metallic bond: an oft-ignored "strong" bond, but one that is responsible for bonding in all metallic materials, virtually 75% of all known elements. It is shown that the "simple" nature of the metallic bond results in "close-packed" crystalline structures. The reader is introduced to the three major metallic structures: cubic close packed, hexagonal close packed, and body centered cubic. Chapter 17 also "hints" at the properties of metallic materials, in particular their melting points and their ductility.

4. CHAPTER XVIII: THE VAN DER WAALS BOND Chapter 18 opens with a question: How can molecular materials, such as O2, H2 and CO2 form liquids, much less solids? Chapter 18 opens with a question: How can molecular materials, such as O2, H2 and CO2 form liquids, much less solids? If a material is composed of "molecules," then the atoms that constitute the molecule have attained the "magical octet" of outer- shell electrons. So, what driving force could there be for molecules to bond to each other? In Chapter 18, one of two possible answers is given—it is called the van der Waals bond. This bond is weak and is associated with "fluctuating dipoles" on individual atoms. If a material is composed of "molecules," then the atoms that constitute the molecule have attained the "magical octet" of outer- shell electrons. So, what driving force could there be for molecules to bond to each other? In Chapter 18, one of two possible answers is given—it is called the van der Waals bond. This bond is weak and is associated with "fluctuating dipoles" on individual atoms. Chapter 18 presents several examples of materials within which the van der Waals bond is of some importance. It also differentiates between intramolecular bonds and intermolecular bonds. These terms are only meaningful in molecular materials (i.e., those in which the strong bond is covalent). Chapter 18 presents several examples of materials within which the van der Waals bond is of some importance. It also differentiates between intramolecular bonds and intermolecular bonds. These terms are only meaningful in molecular materials (i.e., those in which the strong bond is covalent).

5. CHAPTER XIX: THE HYDROGEN BOND The two secondary or weak bonds are van der Waals (Chapter 18) and "hydrogen" (this chapter). Because the hydrogen bond is responsible for the unique properties of water, Chapter 19 concentrates on the hydrogen bonding in the only common liquid on planet Earth: water. The two secondary or weak bonds are van der Waals (Chapter 18) and "hydrogen" (this chapter). Because the hydrogen bond is responsible for the unique properties of water, Chapter 19 concentrates on the hydrogen bonding in the only common liquid on planet Earth: water. The hydrogen bond is shown to result from a permanent dipole that is created on a molecule, which consists of an electropositive and an electronegative atom. Following a description of the hydrogen bond, the unusual properties of water are explained in terms of the relative strengths of the van der Waals bond and the hydrogen bond. Finally, the mechanism for the formation of snowballs is demystified! The hydrogen bond is shown to result from a permanent dipole that is created on a molecule, which consists of an electropositive and an electronegative atom. Following a description of the hydrogen bond, the unusual properties of water are explained in terms of the relative strengths of the van der Waals bond and the hydrogen bond. Finally, the mechanism for the formation of snowballs is demystified!

6. CHAPTER XX: THE STRUCTURE OF POLYMERS The structure of polymers is described with specific reference to the covalent bond, which is "primary" and strong, and to the secondary and weak bonds, van der Waals and hydrogen. The structure of polymers is described with specific reference to the covalent bond, which is "primary" and strong, and to the secondary and weak bonds, van der Waals and hydrogen. A distinction is drawn between thermoplastic polymers and thermosetting polymers. The thermoplastic polymers are described in terms of the primary and secondary bonds, and the differences between linear and branched polymers are presented. The chapter explains thermosetting polymers in terms of the creation of strong, intermolecular bonds that are typically covalent. The crystalline nature and microstructure of polymers is described briefly, and a discussion on the various states of matter, as applied to polymeric materials, is presented. A distinction is drawn between thermoplastic polymers and thermosetting polymers. The thermoplastic polymers are described in terms of the primary and secondary bonds, and the differences between linear and branched polymers are presented. The chapter explains thermosetting polymers in terms of the creation of strong, intermolecular bonds that are typically covalent. The crystalline nature and microstructure of polymers is described briefly, and a discussion on the various states of matter, as applied to polymeric materials, is presented.

7. PRACTICE QUIZ #6: FEEDBACK

9. Q5. The three primary bonds are:  Ionic, which form between a metal and a non-metal (e.g., NaCl).  Covalent, which form between a non-metal and a non-metal (e.g., CO 2 ).  Metallic, which form between atoms of metallic elements (e.g., in bronzes). Use the above information to answer the following question. Oxygen (O 2 ) is a molecular material. True False True. Oxygen is a non-metal and two oxygen atoms bond covalently to each other forming an O 2 molecule. Note that in the O 2 molecule, each bond consists of two bonding pairs (i.e., it is a “double bond”).

10. Q6. Phosphorus has an effective nuclear charge of 15. True False False. The effective nuclear charge of an element is numerically the same as the number of outer-shell electrons, which for phosphorus is 5. Note that the effective nuclear charge is a measure of the force of attraction between the nucleus (positive) and the outer-shell electrons (negative). The “effective” nucleus is taken to be comprised of the “real” nucleus plus all of the inner electron shells. The effective charge on this effective nucleus is given by the number of protons in the real nucleus minus the number of electrons in the inner shells. Each electron in the outer shell is then attracted to the nucleus by the effective nuclear charge.

11. Q7. Which of the following phenomena contribute to the stability of the noble gases? They have closed s and/or p shells, containing 2 and 8 electrons, respectively. For a given period, they are characterized by the highest value of the "effective nuclear charge." They have the highest ionization energies in a particular period. They have closed s and/or p shells, containing 2 and 8 electrons, respectively, and for a given period, they are characterized by the highest value of the "effective nuclear charge." They have closed s and/or p shells, containing 2 and 8 electrons, respectively, and for a given period, they are characterized by the highest value of the "effective nuclear charge," and they have the highest ionization energies in a particular period.

12. The noble gases have closed or filled outer shells (2 for the K-shell and 8 for the remainder). A closed outer shell implies a symmetric electron distribution, with little or no tendency to form dipoles. The effective nuclear charge is equal to 8 (other than for helium, which is 2). This is the highest value for any element within a given period and so the outer-shell electrons are most strongly bonded to the nucleus. Consequently, the ionization energy, which is the energy needed to remove an outer-shell electron, is highest, in a given period, for the noble gas.

13. Q8. Titanium is_____. in Period 4 a transition metal lustrous in Period 4 and a transition metal in Period 4, a transition metal, and lustrous Titanium can be located using its atomic number. It is found in Period 4, between Groups II and III (i.e., it is a transition metal). Because it is a metal, it is lustrous.

15. Q9. The Wayward islanders are just beginning to develop their own version of the periodic table, but many elements are yet to be discovered. The islanders use their own convention to discriminate between periods and groups. For example, in Period Q, several elements are known to exist. Their atomic weights are 40, 44, 46, 48, 50, 52 and 54. Recently, another element has been isolated, and it is known that it belongs to Period Q, but the islanders have lost the information about its atomic weight. Which of the following values do you think is most likely? 49 51 45 53 42 Reference to the listed atomic weights shows that there is a difference of 2 between adjacent elements. However, the "gap" between 40 and 44 is 4, which suggests a missing element. An atomic weight of 42 rather neatly fills this gap!

16. LESSON 6: THE PERIODIC TABLE Electronic Structure of the Elements The Periodic Table Atomic Radii Ionization Energies Metals and Non-Metals

17. INNER AND OUTER SHELLS The maximum number of electrons that may be associated with an inner shell is either equal to or greater than the maximum number of electrons, when that shell is an outer shell. The maximum number of electrons that may be associated with an inner shell is either equal to or greater than the maximum number of electrons, when that shell is an outer shell.

18. ENERGY LEVELS FOR A “MANY ELECTRON” ATOM The K-shell contains 2 electrons only: the 1s electrons. The K-shell contains 2 electrons only: the 1s electrons. The L-shell may contain a maximum of 8 electrons: 2s and 2p. The L-shell may contain a maximum of 8 electrons: 2s and 2p. The M-shell may contain up to 18 electrons: 3s, 3p, and 3d The M-shell may contain up to 18 electrons: 3s, 3p, and 3d However, after the 3s and 3p levels are filled, the next electron occupies a 4s level. However, after the 3s and 3p levels are filled, the next electron occupies a 4s level. The first series of “transition elements” are those elements whose inner 3d shell is being filled. The first series of “transition elements” are those elements whose inner 3d shell is being filled.

19. ELECTRONIC STRUCTURES The K-shell contains 2 electrons only: the 1s electrons. The K-shell contains 2 electrons only: the 1s electrons. The L-shell may contain a maximum of 8 electrons: 2s and 2p. The L-shell may contain a maximum of 8 electrons: 2s and 2p. The M-shell may contain up to 18 electrons: 3s, 3p, and 3d. The M-shell may contain up to 18 electrons: 3s, 3p, and 3d. However, after the 3s and 3p levels are filled, the next electron occupies a 4s level. However, after the 3s and 3p levels are filled, the next electron occupies a 4s level. The first series of “transition elements” are those elements whose inner 3d shell is being filled. The first series of “transition elements” are those elements whose inner 3d shell is being filled.

20. THE GROUP IV ELEMENTS Carbon: Period 2 Silicon: Period 3 Germanium: Period 4

21. ABBREVIATED PERIODIC TABLE

22. THE MAGICAL OCTET! For all outer shells, other than the K-shell, an atom will try to attain a full outer shell, consisting of eight electrons (the K-shell is complete with only two). For all outer shells, other than the K-shell, an atom will try to attain a full outer shell, consisting of eight electrons (the K-shell is complete with only two). An atom will seek this magical octet by donating, accepting, or sharing outer-shell electrons with other atoms. An atom will seek this magical octet by donating, accepting, or sharing outer-shell electrons with other atoms. It is this donating, accepting, or sharing of electrons that gives rise to “bonding”! It is this donating, accepting, or sharing of electrons that gives rise to “bonding”!

23. METALS AND NON-METALS Metals will be defined as electron donors and non- metals will be defined as electron acceptors. Metals will be defined as electron donors and non- metals will be defined as electron acceptors. In a very crude first approximation, we shall assume that it is relatively easy to lose a small number of outer-shell electrons and also relatively easy to gain a small number. In a very crude first approximation, we shall assume that it is relatively easy to lose a small number of outer-shell electrons and also relatively easy to gain a small number. Hence, “define” (?) a metal as an element that contains three outer-shell electrons or fewer. Hence, “define” (?) a metal as an element that contains three outer-shell electrons or fewer. Then a non-metal will contain five or more outer-shell electrons (?). Then a non-metal will contain five or more outer-shell electrons (?). This leaves us with the Group IV elements! This leaves us with the Group IV elements!

24. METALS AND NON-METALS: A FIRST ATTEMPT!

25. EFFECTIVE NUCLEAR CHARGE The “effective nuclear charge” is a measure of how strongly the outer-shell electrons are attracted to the nucleus. The “effective nuclear charge” is a measure of how strongly the outer-shell electrons are attracted to the nucleus. As the effective nuclear charge increases, the outer- shell electrons get closer to the nucleus, and the radius of the atom decreases. As the effective nuclear charge increases, the outer- shell electrons get closer to the nucleus, and the radius of the atom decreases. As the outer-shell electrons get closer to the nucleus, they become more difficult to “remove” from the atom, and the “ionization energy” increases. As the outer-shell electrons get closer to the nucleus, they become more difficult to “remove” from the atom, and the “ionization energy” increases. METALS TEND TO HAVE LOW IONIZATION ENERGIES! METALS TEND TO HAVE LOW IONIZATION ENERGIES!

26. EFFECTIVE NUCLEAR CHARGE: PERIOD 3

27. EFFECTIVE NUCLEAR CHARGES, ATOMIC RADII, IONIZATION ENERGIES, ETC. The effective nuclear charge in Period 3 increases going from left to right. The effective nuclear charge in Period 3 increases going from left to right. We would therefore predict that in going across Period 3, for example, the atomic radii will decrease. We would therefore predict that in going across Period 3, for example, the atomic radii will decrease. Hence, the ionization energies increase going from left to right! Hence, the ionization energies increase going from left to right! In going “north to south” in a given group, the effective nuclear charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases. In going “north to south” in a given group, the effective nuclear charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases. Hence, ionization energies decrease going north to south in a given group! Hence, ionization energies decrease going north to south in a given group!

28. ATOMIC RADII: A PERIODIC FUNCTION a) The Group I Elements b) The Period 3 Elements

29. THE ATOMIC RADII OF THE PERIOD 4 ELEMENTS

30. EFFECTIVE NUCLEAR CHARGES, ATOMIC RADII, IONIZATION ENERGIES, ETC. The effective nuclear charge in Period 3 increases going from left to right. The effective nuclear charge in Period 3 increases going from left to right. Therefore, we would predict that in going across Period 3, for example, the atomic radii will decrease. Therefore, we would predict that in going across Period 3, for example, the atomic radii will decrease. Hence, the ionization energies increase going from left to right! Hence, the ionization energies increase going from left to right! In going “north to south” in a given group, the effective nuclear charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases. In going “north to south” in a given group, the effective nuclear charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases. Hence, ionization energies decrease going north to south in a given group! Hence, ionization energies decrease going north to south in a given group!

31. IONIZATION ENERGIES: METALS AND NON-METALS

32. THE GROUP IV ELEMENTS Carbon: Period 2 Silicon: Period 3 Germanium: Period 4

33. EFFECTIVE NUCLEAR CHARGES, ATOMIC RADII, IONIZATION ENERGIES, ETC. The effective nuclear charge in Period 3 increases going from left to right. The effective nuclear charge in Period 3 increases going from left to right. Therefore, we would predict that, in going across Period 3, for example. the atomic radii will decrease Therefore, we would predict that, in going across Period 3, for example. the atomic radii will decrease Hence, the ionization energies increase going from left to right! Hence, the ionization energies increase going from left to right! In going “north to south” in a given group, the effective nuclear charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases. In going “north to south” in a given group, the effective nuclear charge remains the same, but the outer shell becomes more remote from the nucleus as the number of inner shells increases. Hence, ionization energies decrease going north to south in a given group! Hence, ionization energies decrease going north to south in a given group!

34. THE GROUP IV ELEMENTS: IONIZATION ENERGIES

35. THE GROUP IV ELEMENTS For carbon, the outer shell is the L-shell. Hence, the four outer-shell electrons are strongly bound to the nucleus and the ionization energy is very high. Carbon in the guise of diamond is a prototypical non-metal. For carbon, the outer shell is the L-shell. Hence, the four outer-shell electrons are strongly bound to the nucleus and the ionization energy is very high. Carbon in the guise of diamond is a prototypical non-metal. For lead, the outer shell is the P-shell. The outer-shell electrons are only weakly bound and lead is a typical metal. For lead, the outer shell is the P-shell. The outer-shell electrons are only weakly bound and lead is a typical metal. IN THE MIDDLE ARE THE SEMICONDUCTORS: SILICON AND GERMANIUM. IN THE MIDDLE ARE THE SEMICONDUCTORS: SILICON AND GERMANIUM.

36. ATOMIC RADII AND IONIZATION ENERGIES: PERIODIC PROPERTIES

37. IONIZATION ENERGIES: METALS AND NON-METALS

38. METALS AND NON-METALS