If you are not registered for ChE 361 Please come see me.
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Transcript of If you are not registered for ChE 361 Please come see me.
If you are not registered for ChE 361
Please come see me
About Clicker Quizzes:
1) Review previous lectures
2) Review reading assignment
3) Assess understanding of today’s discussion
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Types of Bonding
• Ionic
• Covalent
• Metallic
• Van der Waals (Secondary)
The Periodic TableColumns: Similar Valence Structure
Adapted from Fig. 2.6, Callister & Rethwisch 8e.
Electropositive elements:Readily give up electronsto become + ions.
Electronegative elements:Readily acquire electronsto become - ions.
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e-
ine
rt g
ase
s
acc
ept
1e
-
acc
ept
2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
ClS
Li Be
H
Na Mg
BaCs
RaFr
CaK Sc
SrRb Y
Some electron configurations are especially stable.(Think “noble gases”)
Rule #2: Stable Configurations
Example: Na, Cl
Opposites attract
Rule #1: Electrical Neutrality
1) Ionic Bonding
Atoms take/give electrons to neighbor– Often 1 metallic & 1 non-metallic (Elements from opposite sides of table)
2) Covalent bonding
Atoms Share Electrons
Example: H2O
2) Covalent bondingAdjacent atoms share
electrons to achieve stable e- configuration
Reality check
ionic covalent
Nature of the bond reported as:Percent ionic character
3) Metallic Bonding• Share electrons (“sea of
electrons”)
• Orbitals never completely filled:Electrons jump from atom to atom
Section 2.7
Secondary or Van der Waals
Bonding
Rule #3: Dipoles almost always
occur
4) Secondary (Van der Waals) bonding
• Weak compared to primary bonds
• Can significantly affect material properties
4) Secondary (Van der Waals) bonding
+Ioncore
–
–
Fluctuating induced dipole moments
–
Ion core
Before:
After:
Ion core
Ion core +
• Permanent Dipole BondsPermanent dipole moments in the molecule.Bonds stronger than for Fluctuating
• Example: H2O
OHH +– O
HH +– O
HH +–
4) Secondary (Van der Waals) bonding
For which will VdW forces have the strongest influence on properties?Covalent bond: Where a rod meets a ball
A.Graphite(Carbon)
B.Diamond(Carbon)
Sections 3.1–3.4; 3.7
Structure of Crystalline
Solids
Cubic xl Structures
Unit Cell
• Smallest structural unit that generates a 3-D xl (if repeated).
• 7 Crystal Systems—Only 7 unit cell shapes for all xl structures.
Table 3.2Crystal Systems
Table 3.2, cont’d
Crystal Systems, cont’d
Unit cell
Cubic Systema = b = c
º
Fig. 3.4
Atomic Packing Factor
APF = volume of atoms in unit cell
total volume of unit cell
Metallic xl Structures
1) Face-Centered Cubic (FCC)
2) Body-Centered Cubic (BCC)
3) Hexagonal Close-Packed (HCP)
FCCAtoms at 8 corners & 6 faces
Equivalent of ? whole atoms.
Atomic Packing Factor (APF)= .74
Fig. 3.1
FCC Cubic structure
STM of PlatinumDept. Kings.edu/chemlab, Property of IBM
A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level.
What’s an STM image?
Atoms….
You are under our control!
• 1990: IBM scientist Don Eigler used an STM to move single xenon atoms on a nickel surface
•The engineers moved 35 atoms to spell out "IBM" in a 10 micrometer logo.
FCC examples
Lab-grown copper (SEM)0.3 mm
Etched Aluminum (SEM)
GoldGalena (Pb ore)
A scanning electron microscope (SEM) produces images by scanning a sample with a focused beam of electrons. Yields topography and composition.
What’s an SEM image?
BCC
Atoms at 8 corners & 1 in center of
cube
Equivalent of ? whole atoms
APF = .68Fig. 3.2
BCC Cubic structure
STM of Aluminum (100) surface
https://wiki.fysik.dtu.dk/dacapo/Examples
BCC examples
Molybdenum Iron
Metallic xl Structures
1) Face-Centered Cubic (FCC)Cu, Al, Ag, Au, Pb, Ni, Pt
2) Body-Centered Cubic (BCC)Na, Fe, Cr, Mo, W
3) Hexagonal Close-Packed (HCP)Ti, Zn, Cd, Co, Mg
HexagonalSystem
a1 = a2 = a3 ≠ z
º
º
Fig. 3.7
HCP
Atoms at 12 corners, 3 in interior, 2 centered on basal planes
Equivalent of ? whole atoms
(APF)= .74Fig. 3.3
Hexagonal structure
STM of Nickel surface structure.
Dept. Kings.edu/chemlab, Property of IBM
Zinc hand sample
Hexagonal structure
SEM of Fine Cadmium powder
http://www.sciencephoto.com/media/8998/enlarge
SEM of ZnO nanowireshttp://www.lac.tu-clausthal.de/en/arbeitsgruppen/angewandte-photonik-
lac/projekte/zinc-oxide-nanowires-for-photonic-applications/
Hexagonal structure
HCP Examples
Titanium crystals
Cadmium crystal bar
Magnesium (SEM)
Atomic Packing Factors
BCC = 0.68 FCC = 0.74 HCP = 0.74