Transcript - Dutton e-Education Institute Courseware

LECTURE 5.2
LECTURE OUTLINE

Weekly Reading
 Prototype Practice Quiz 5: Feedback
 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

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Chapter 14 also discriminates between metals and nonmetals.
Metals are defined as “electron donors,” while nonmetals 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 1938. 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%
UNIT 5 PROTOTYPE EXAM
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DISCRIMINATION
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Q1. A neutral atom of sodium (1123 Na) has _____ electrons.
<a+> 11
<b> 12
<c> 23
<d> 34
<e> 8
<F> 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.
a
T1
Temperature
T2
b
c
d
e
1)
2)
Time
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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 “T2” corresponds to ______.
<a> the melting point of the ceramic
<b+> the glass-transition temperature
<c> the dew-point temperature
<d> absolute zero
<e> the Curie temperature
a
T1
Temperature
T2
b
c
d
e
1)
2)
Time

<F> Temperature “T1” corresponds to the melting point of the ceramic. It
may be identified as such, because there is a discontinuous change in
volume at “T1.” Discontinuous changes in volume are always associated
with the liquid to crystalline transformation. Note that temperature “T2” is
associated with the “glass transition temperature,” the temperature at which
the amorphous ceramic becomes “rigid” and will no longer flow.
Liquid
Volu m e
a)
b)
c)
T1
Te m pe ratuer
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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+> a crystalline polymorph
<b> the glass
<c> the liquid
<d> the gas
Liquid
Volu m e
a)
b)
c)
T1
Te m pe ratuer

<F> 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.
?
a)
b)
c)
d)
e)
Figure 5.
Figure 4.
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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?
<a> Figure 5a
<b> Figure 5b
<c> Figure 5c
<d+> Figure 5d
<e> Figure 5e
?
a)

b)
c)
d)
e)
<F> The form that best describes the atomic motif of
Figure 4 is a hexagon.
a)
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b)
c)
d)
e)
f)
g)
Q19. Figure 8 shows "Lewis-Dot" notations for
certain representative elements. Which figure is
appropriate for phosphorus (1531P)?
<a> Figure 8d
<b+> Figure 8e
<c> Figure 8f
<d> Figure 8g
<e> Figure 8h
h)
a)

b)
c)
d)
e)
f)
g)
h)
<F> Reference to Table 12.1 shows that the Kshell 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
 Definition of a Molecule
 Definition of a Monomer
 Definition of a Crystal
 Definition of a Glass
 Molecular or Not?
 Matter and Form
Atoms
together
with
Geometric
Form
is not
which has
both
Single Atom
Number
may be
is
not
need
not be
Stable
plus
No
Translational
Form
creates
Liquid/
Glass
Macromolecule
plus
Translational
Form
which is
is both
Electrically
Neutral
creates
Monomer
with
with
Periodic
is
may
also be
Molecule
Shape
Lattice
creates
Crystalline Material
plus
plus
may
create
Linear 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.
MOLECULES, MONOMERS,
CRYSTALS, ETC.

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 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 106 monomers.
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.
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.
 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.
 It is now impossible to pack the macromolecules to create a crystalline
polymer.
 The result is amorphous low-density polyethylene (LDPE).
Atoms
together
with
Geometric
Form
is not
which has
both
Single Atom
Number
may be
is
not
need
not be
Stable
plus
No
Translational
Form
creates
Liquid/
Glass
?
Macromolecule
plus
Translational
Form
which is
is both
Electrically
Neutral
creates
Monomer
with
with
Periodic
is
may
also be
Molecule
Shape
Lattice
creates
Crystalline Material
plus
plus
may
create
Linear Form
MATTER AND FORM I

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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.
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!
EGYPTIAN BRICKMAKING:
MATTER AND FORM

Geometric
Form
Primal
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.
Together:
matter + form = material
(monomer)
MATTER AND FORM III
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!
 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
Monomer
a)
Running Bond
+
Lattice
Unit Cell
Dumb Bond
b)
+
Odd Bond
c)
+
MATTER + FORM = MATERIAL:
UBIQUITOUS SILICA I
Matter
+
Form
Monomer
+
a)



b)
c)
The “primal matter” consists of “formless” silicon plus
oxygen atoms.
The geometric form that is imposed on this matter is a
tetrahedron.
This yields the silica monomer.
MATTER + FORM = MATERIAL:
UBIQUITOUS SILICA II
+
Monomer
a)


+
Lattice
b)
Structure
c)
The second, periodic form is a lattice, whose shape is cubic.
This periodic form creates cristobalite.