Chapter 4
Nanomaterials & Bonding
NANO 101
Introduction to Nanotechnology
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Quiz Wednesday
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MC/Short Answer (10 questions, 30 pts)
Free Response (3 questions, 24 pts)
Calculations (3 questions, 21 pts)
Formula sheet, similar to extra practice
Bring a scientific calculator, not a cellphone,
graphing calculators are okay
• You will have 2 hrs, shouldn’t take the entire
time.
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Materials
• Matter with a useful purpose
Matter is…
• Anything that has mass and occupies space
• Made up of atoms and/or molecules
• To make molecules and solids – need chemical bonds
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Models of the Atom
J.J. Thomson
Rutherford
Proton
Neutron
Current model
Electron
Charge
Mass
(kg)
Location
~1.673*10-27 ~1.675*10-27 ~9.11*10-31
nucleus
nucleus
“clouds”
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Covalent Bonding
• Minimum energy:
Energy
• Attractive and repulsive
forces cancel out
• Binding Energy
• Separation between
atoms when bonded
• Interatomic distance
Interatomic Distance
• Bond length
http://voh.chem.ucla.edu/vohtar/winter02/20A/lecture5.htm
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Covalent Compounds
Atoms share electrons to form molecules
H
+
H
H H
H
H
H2
Bonding electrons
F
+
F
F F
F
F
F2
Lone pair electrons
Covalent bonds usually between nonmetal + nonmetal
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Ionic Bonding
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Forms salts
Transfer of electrons
Electrostatic attraction
No sharing of electrons
Non-Metal:
Accepts electron
anion
Metal:
Donates electrons
Fluorine
Sodium
cation
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Ionic solids
• Examples: NaCl (table salt), (NH₄)₂CO₃
• Properties:
– High melting point
NaCl
– Very hard
– Poor conductivity
– Water soluble
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Organic Compounds
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C-C bond length ~ 0.15 nm
C-H bond length ~ 0.11 nm
Simplest organic molecule: methane CH4
Octane end H to end H = 1.6 nm
Covalent Solids
• Examples: Diamond, Graphene, Silicon carbide,
Boron Nitride
SiC in bulletproof vests
• Properties:
Diamond =
carbon
molecular solid
– Hard
– High melting point
– Low conductivity (graphene is exception)
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Ionic/Covalent Scale
• Electronegativity – How much an atom wants to
gain electrons.
Same electronegativity
Very different
electronegativity
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Metallic Bonding
Atom cores
• Electrical Conductors
• Thermal Conductors
• Ductile materials
Sea of valence electrons
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Intermolecular Forces
Van der Waals forces
• dipole-dipole
• if between H & N, O, F
hydrogen bond
H
H
O
H
O
H
O
H
H
• dipole-induced dipole
• induced dipole-induced dipole
(London Dispersion forces)
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Graphite
• Intramolecular vs intermolecular
– Solid lines = covalent bonds = intramolecular foce
– Dotted lines = Van der Waals forces =
intermolecular force
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Strength of London Dispersion
• Propane
• Octane
• Paraffin
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Quiz Wednesday
•
•
•
•
•
MC/Short Answer (10 questions, 30 pts)
Free Response (3 questions, 24 pts)
Calculations (3 questions, 21 pts)
Formula sheet, similar to extra practice
Bring a scientific calculator, not a cellphone,
graphing calculators are okay
• You will have 2 hrs, shouldn’t take the entire
time.
16
Small Structures
• Particles
• Wires
• Films, Layers, Coatings
• Porous Materials
• Small Grained Materials
• Molecules
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Particles
• Small particles are mostly surface
• Bulk solids typically < 1% surface atoms
• Small nanoparticles can have ~90% surface atoms
• Van der Waals forces dominates
• Mostly interparticle interactions (fewer bonds)
• More reactive
• Useful as catalysts
Source: Younan Xia,
Washington University
Source: Seoul National University
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Wires / Tubes
Source: Evans Group, University of Leeds
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Source: Science Buzz, Science Museum of Minn.
Electronics
Optics
Strength-based applications
Can characterize by aspect ratio (length/(width
or diameter))
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Films, Layers, Coatings
Surface is where all interactions
and reactions take place.
Self-Assembled Monolayers:
Ordered arrangement of molecules
that occurs spontaneously
tail
http://phys.org/news85328131.html#nRlv
backbone
head
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Molecular Self Assembly
Mechanisms for much chemistry
Happens due to:
• Intermolecular interactions
– Hydrogen bonding
– hydrophobicity and hydrophilicity
– Solvency
“like dissolves like”
• Specific covalent reactions
– Functionalization
– Ex. Thiols and coinage metals
Looking Ahead
• Lab #1 due Thursday 4/23
• Homework #3 due Monday 4/27
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Pre-Lab for Thursday
• Bottom – up Nanoparticle Synthesis
– Starting with molecular precursors
– Chemistry! Will build the nanoparticles
• Comprehensive study on synthesis and properties
of colloidal gold published by Faraday (1857)
• Classic method (1985, Turkevich)
– Precursor: dilute chlorauric acid (HAuCl4)
– Reducing agent: sodium citrate (NaC6H5O7)
– Reaction temperature: 100 °C
– Product: stable, uniform, ~20 nm particles
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Gold NP Biosensors
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Make a salt or sugar sensor
• What type of bonds hold
the citrate to the gold
nanoparticle?
• What is the difference
between sugar
dissolved in water and
salt dissolved in water?
Dalton Trans., 2014,43, 5054-5061
• Observe color visually
• Observe color with
spectrometer
http://www.cytodiagnostics.com/store/pc/Gold-Nanoparticle-Properties-d2.htm
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