LECTURE 5.2

LECTURE OUTLINE Weekly Reading Weekly Reading Prototype Practice Quiz 5: Feedback Prototype Practice Quiz 5: Feedback Molecules, Monomers, Crystals, Etc. (Part II) Molecules, Monomers, Crystals, Etc. (Part II)

CHAPTER XIV: THE PERIODIC TABLE Chapter 14 rationalizes the "architecture" of the Periodic Table in terms of the electronic structures of the elements. It is shown that there are two major rhythms, or periodicities, when the elements are listed by atomic number. These rhythms are dictated by: the principal quantum number of the outer shell the number of electrons in that outer shell The first rhythm determines the Period within which an element will be located, and the second rhythm determines the Group to which an element will belong.

CHAPTER XIV: THE PERIODIC TABLE Chapter 14 also discriminates between metals and non- metals. Metals are defined as “electron donors,” while non- metals are defined as “electron acceptors.” The simple interpretation of the Periodic Table and the “conceptual definitions” of a metal and a non-metal is shown to permit the classification of virtually all elements as either metallic or non-metallic. Finally, it is noted that the Group IV elements—carbon, silicon, germanium, tin, and lead—are on the borderline between metallic and non-metallic behavior. Semiconductors are found in these Group IV elements.

CHAPTER XV: THE IONIC BOND Chapter 15 is the first in a series of five chapters on the nature of the bonds that develop between adjacent atoms, ions, molecules, and/or monomers. The chapter begins by presenting a glossary of terms that will appear throughout the remainder of the text and forging a link between bond types and the Periodic Table. The remainder of the chapter is devoted to the ionic bond. Several aspects of this bond are described, including: the nature of the ionic bond the ionic bond and crystalline ceramics the use of the Lewis notation for electronic bookkeeping the relationship between bond strength and material properties

CHAPTER XV: THE IONIC BOND The last named topic—the link between a fundamental structural quantity (the ionic bond) and material properties—is illustrated with respect to data from a veritable tome published in Prototypical properties evaluated include Mohs hardness and melting point (both of which were first introduced in Chapter 3).

CHAPTER XVI: COVALENT BONDING Oftentimes, the only bond that is ever mentioned in high school is the covalent bond. The covalent bond and the molecule are shown to be inextricably linked, and Chapter 16 defines "the molecule" in terms of the "covalent bond." It is argued that, in general, molecular materials are thoroughly useless as engineering materials because of their low melting points. However, it is also shown that covalently bonded network solids may have extremely high melting points.

CHAPTER XVI: COVALENT BONDING Chapter 16 introduces the reader to the concept of a “molecular weight” as contrasted with an “atomic weight.” It finishes with a description of an atomic model, courtesy of the American chemist Gilbert Newton Lewis, which was first formulated in 1902—a brief five years after the discovery of the electron. This remarkably sophisticated model of the atom predicted the electronic structures of many elements more than twenty years before the quantum mechanical description of the electronic structures.

PRACTICE QUIZ #5: FEEDBACK

Quiz Average: 53%

Q1. A neutral atom of sodium ( Na) has _____ electrons Reference to Section 12.4 shows that the subscript is the atomic number of the element, which is numerically equal to the number of protons in the nucleus. It is also equal to the number of electrons for a neutral atom. The superscript is the approximate atomic weight, which is numerically equal to the number of protons plus the average number of neutrons. For Na, the atomic number is 11—this is the number of electrons.

Q7. Figure 1 shows the cooling curves for a ceramic material. There are two different cooling rates: cooling rate # 1 is relatively slow, while cooling rate # 2 is somewhat more rapid. Temperature “T 2 ” corresponds to ______. the melting point of the ceramic the glass-transition temperature the dew-point temperature absolute zero the Curie temperature

Temperature “T 1 ” corresponds to the melting point of the ceramic. It may be identified as such, because there is a discontinuous change in volume at “T 1. ” Discontinuous changes in volume are always associated with the liquid to crystalline transformation. Note that temperature “T 2 ” is associated with the “glass transition temperature,” the temperature at which the amorphous ceramic becomes “rigid” and will no longer flow.

Q8. A certain ceramic is polymorphic and can exist as two crystalline solid forms. The ceramic can also exist as a gas, a liquid, and as a glassy solid. Figure 2 shows volume-temperature plots for this ceramic for both slow and moderately fast cooling. Figures 3a–c are schematic diagrams of three “states” for the ceramic. Figure 3a represents ________. a crystalline polymorph the glass the liquid the gas

Figure 3a shows a crystalline solid. The atoms are arranged in a periodic, regularly repeating fashion. The solid is said to display a “regular form.” Note that Figures 3b and c show amorphous materials, and we may only differentiate between the two possibilities on the basis of their relative specific gravities.

Q13. Figure 5 shows various forms that may be used to describe solid materials. They are, in sequence, a rectangle, a square, a pentagon, a triangle, a hexagon, and a question mark. The last implies the lack of form. Note that the triangle and the hexagon are shown together as part d, because the two forms are usually interchangeable. Note that two or more forms may be possible. For example a single pattern might be describable as both a rectangle and a square. If that is the case, choose the square. Which form best describes that of Figure 4? Q13. Figure 5 shows various forms that may be used to describe solid materials. They are, in sequence, a rectangle, a square, a pentagon, a triangle, a hexagon, and a question mark. The last implies the lack of form. Note that the triangle and the hexagon are shown together as part d, because the two forms are usually interchangeable. Note that two or more forms may be possible. For example a single pattern might be describable as both a rectangle and a square. If that is the case, choose the square. Which form best describes that of Figure 4? Figure 5a Figure 5a Figure 5b Figure 5b Figure 5c Figure 5c Figure 5d Figure 5d Figure 5e Figure 4. Figure 5.

The form that best describes the atomic motif of Figure 4 is a hexagon.

Q19. Figure 8 shows "Lewis-Dot" notations for certain representative elements. Which figure is appropriate for phosphorus ( P)? Q19. Figure 8 shows "Lewis-Dot" notations for certain representative elements. Which figure is appropriate for phosphorus ( P)? Figure 8d Figure 8d Figure 8e Figure 8e Figure 8f Figure 8f Figure 8g Figure 8g Figure 8h

Reference to Table 12.1 shows that the K- shell may only contain two electrons, and the L-shell a maximum of eight. This leaves a total of five electrons to occupy the M-shell.

MOLECULES, MONOMERS, CRYSTALS, ETC. (PART II) Definitions and Atomic Models

MOLECULES, MONOMERS, CRYSTALS, ETC. The Hierarchical Levels of Structure The Hierarchical Levels of Structure Definition of a Molecule Definition of a Molecule Definition of a Monomer Definition of a Monomer Definition of a Crystal Definition of a Crystal Definition of a Glass Definition of a Glass Molecular or Not? Molecular or Not? Matter and Form Matter and Form

DEFINITION OF A CRYSTAL A crystal is a solid material in which the atoms/monomers/molecules are arranged periodically, in a perfectly repeating form or pattern. A crystal can be represented by a “lattice” of points in space. A crystal is a solid material in which the atoms/monomers/molecules are arranged periodically, in a perfectly repeating form or pattern. A crystal can be represented by a “lattice” of points in space.

MOLECULES, MONOMERS, CRYSTALS, ETC. The crystal structure of diamond is built from many monomers, creating a “cubic” structure. The crystal structure of diamond is built from many monomers, creating a “cubic” structure. The “unit cell” of this structure is shown by the yellow straws. The “unit cell” of this structure is shown by the yellow straws. The covalent bonds are shown by the silver spokes. The covalent bonds are shown by the silver spokes.

MOLECULES, MONOMERS, CRYSTALS, ETC. A small fragment of a macromolecule of polyethylene ( a “pentamer”). A real macromolecule of PE might contain 10 6 monomers. A small fragment of a macromolecule of polyethylene ( a “pentamer”). A real macromolecule of PE might contain 10 6 monomers. Packing of these linear macromolecules can produce a crystalline polymer, called high-density polyethylene (HDPE). Packing of these linear macromolecules can produce a crystalline polymer, called high-density polyethylene (HDPE). Note that for “polymers” the monomer is much smaller than the (macro)molecule. Note that for “polymers” the monomer is much smaller than the (macro)molecule.

DEFINITION OF A GLASS A glass is amorphous, or without form or shape. The atoms/monomers/molecules in a glass are not arranged periodically. A glass has the structure of a liquid, but the properties of a solid. A glass is amorphous, or without form or shape. The atoms/monomers/molecules in a glass are not arranged periodically. A glass has the structure of a liquid, but the properties of a solid. Glasses are brittle! Glasses are brittle!

MOLECULES, MONOMERS, CRYSTALS, ETC. However, the macromolecules need not be straight. They may be curved while still retaining the tetrahedral geometry of the monomers. However, the macromolecules need not be straight. They may be curved while still retaining the tetrahedral geometry of the monomers. It is now impossible to pack the macromolecules to create a crystalline polymer. It is now impossible to pack the macromolecules to create a crystalline polymer. The result is amorphous low-density polyethylene (LDPE). The result is amorphous low-density polyethylene (LDPE).

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MATTER AND FORM I Any material may be considered the superposition of “form” on “matter.” Any material may be considered the superposition of “form” on “matter.” Matter is “ponderable,” it can be touched, weighed, and felt. However, this “matter” is shapeless. Matter is “ponderable,” it can be touched, weighed, and felt. However, this “matter” is shapeless. Form is antithetical to matter. It is imponderable, but it confers shape or form to matter. Form is antithetical to matter. It is imponderable, but it confers shape or form to matter. Two forms may be superimposed on “matter”: the first is geometric, the second can be periodic! Two forms may be superimposed on “matter”: the first is geometric, the second can be periodic!

EGYPTIAN BRICKMAKING: MATTER AND FORM The brick may be considered in terms of “primal matter” or “stuff” with a geometric “form” which gives shape to the “formless” matter. The brick may be considered in terms of “primal matter” or “stuff” with a geometric “form” which gives shape to the “formless” matter. The “matter” consists of “brick atoms.” The geometric form describes the shape of the brick—an insensible parallelepiped. The “matter” consists of “brick atoms.” The geometric form describes the shape of the brick—an insensible parallelepiped. Together: Together: matter + form = material (monomer) Primal Matter Geometric Form

MATTER AND FORM III But our final “object” is the brick wall. But our final “object” is the brick wall. I must impose a second (periodic) form on the “matter,” where the “matter” is now defined as the product of the first application of form to matter: the brick, or monomer! I must impose a second (periodic) form on the “matter,” where the “matter” is now defined as the product of the first application of form to matter: the brick, or monomer! This second form is periodic and is a lattice pattern, which describes the way in which the bricks are assembled to create the wall. This second form is periodic and is a lattice pattern, which describes the way in which the bricks are assembled to create the wall.

MATTER + FORM = MATERIAL Lattice Unit Cell Monomer

MATTER + FORM = MATERIAL: UBIQUITOUS SILICA I The “primal matter” consists of “formless” silicon plus The “primal matter” consists of “formless” silicon plus oxygen atoms. The geometric form that is imposed on this matter is a tetrahedron. The geometric form that is imposed on this matter is a tetrahedron. This yields the silica monomer. This yields the silica monomer.

MATTER + FORM = MATERIAL: UBIQUITOUS SILICA II The second, periodic form is a lattice, whose shape is cubic. The second, periodic form is a lattice, whose shape is cubic. This periodic form creates cristobalite. This periodic form creates cristobalite.