Exam review

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Types of Bonding

  • Ionic
  • Covalent
  • Metallic
  • Van der Waals (Secondary)

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The Periodic Table

Columns: Similar Valence Structure

Adapted from Fig. 2.6, Callister & Rethwisch 8e.

Electropositive elements:

Readily give up electrons

to become + ions.

Electronegative elements:

Readily acquire electrons

to become - ions.

give up 1e-

give up 2e-

give up 3e-

inert gases

accept 1e-

accept 2e-

O

Se

Te

Po

At

I

Br

He

Ne

Ar

Kr

Xe

Rn

F

Cl

S

Li

Be

H

Na

Mg

Ba

Cs

Ra

Fr

Ca

K

Sc

Sr

Rb

Y

*

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Some electron configurations

are especially stable.

(Think “noble gases”)

Rule #2: Stable Configurations

f06_02_pg23

Example: Na, Cl

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f06_02_pg23.jpg

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)

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2) Covalent bonding

Atoms Share Electrons

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f06_02_pg23

Example: H2O

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f06_02_pg23.jpg

2) Covalent bonding

Adjacent atoms share electrons to achieve stable e- configuration

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Reality check

ionic

covalent

Nature of the bond reported as:

Percent ionic character

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3) Metallic Bonding

  • Share electrons (“sea of electrons”)
  • Orbitals never completely filled:
    Electrons jump from atom to atom

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Section 2.7

Secondary or Van der Waals Bonding

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Rule #3: Dipoles
almost always
occur

4) Secondary (Van der Waals) bonding

  • Weak compared to primary bonds

  • Can significantly affect material properties

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4) Secondary (Van der Waals) bonding

+

Ion

core

–

–

Fluctuating induced dipole moments

–

Ion

core

Before:

After:

Ion

core

Ion

core

+

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  • Permanent Dipole Bonds

Permanent dipole moments in the molecule.

Bonds stronger than for Fluctuating

  • Example: H2O

O

H

H

+

–

O

H

H

+

–

O

H

H

+

–

4) Secondary (Van der Waals) bonding

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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)

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Sections 3.1–3.4; 3.7

Structure of Crystalline Solids

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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 3.2

Crystal Systems

Table 3.2, cont’d

Crystal Systems, cont’d

f04_03_pg46

Unit cell

Cubic System

a = b = c

a = b = g = 90º

Fig. 3.4

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f04_03_pg46.jpg

Atomic Packing Factor

APF = volume of atoms in unit cell

total volume of unit cell

Metallic xl Structures

Face-Centered Cubic (FCC)

Body-Centered Cubic (BCC)

Hexagonal Close-Packed (HCP)

f02_03_pg42

FCC

Atoms at 8 corners & 6 faces

Equivalent of

? whole atoms.

Atomic Packing Factor

(APF)= .74

Fig. 3.1

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f02_03_pg42.jpg

FCC Cubic structure

STM of Platinum

Dept. 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?

http://en.wikipedia.org/wiki/Scanning_tunneling_microscope

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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)

Etched Aluminum (SEM)

Gold

Galena (Pb ore)

0.3 mm

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?

f02_03_pg42

BCC

Atoms at 8 corners & 1 in center of cube

Equivalent of ? whole atoms

APF = .68

Fig. 3.2

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f02_03_pg42.jpg

BCC Cubic structure

STM of Aluminum (100) surface

https://wiki.fysik.dtu.dk/dacapo/Examples

BCC examples

Molybdenum

Iron

Metallic xl Structures

Face-Centered Cubic (FCC)

Cu, Al, Ag, Au, Pb, Ni, Pt

Body-Centered Cubic (BCC)

Na, Fe, Cr, Mo, W

Hexagonal Close-Packed (HCP)

Ti, Zn, Cd, Co, Mg

f07_03_pg54

Hexagonal
System

a1 = a2 = a3 ≠ z

  • = 90º

g = 120º

Fig. 3.7

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f07_03_pg54.jpg

f03_03_pg43

HCP

Atoms at 12 corners, 3 in interior,

2 centered on basal planes

Equivalent of ? whole atoms

(APF)= .74

Fig. 3.3

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f03_03_pg43.jpg

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 nanowires

http://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