Chapter 4Nanomaterials & Bonding

NANO 101Introduction to Nanotechnology

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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.

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

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Rutherford Current model

Proton Neutron Electron

Charge

Mass(kg)

~1.673*10-

27

~1.675*10-

27 ~9.11*10-31

Location nucleus nucleus “clouds”

Covalent Bonding

• Minimum energy: • Attractive and

repulsive forces cancel out

• Binding Energy

• Separation between atoms when bonded • Interatomic distance• Bond length

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Ene

rgy

http://voh.chem.ucla.edu/vohtar/winter02/20A/lecture5.htm

Interatomic Distance

Covalent CompoundsAtoms share electrons to form

molecules

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H H+ H H H H H2

F F+ FF FF F2

Lone pair electrons

Covalent bonds usually between nonmetal + nonmetal

Bonding electrons

Ionic Bonding• Forms salts• Transfer of electrons• Electrostatic attraction• No sharing of electrons

Non-Metal:Accepts electron

Sodium

Metal: Donates electrons

Fluorineanion cation

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Ionic solids• Examples: NaCl (table salt), (NH₄)₂CO₃• Properties:

– High melting point– Very hard– Poor conductivity– Water soluble

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NaCl

Organic Compounds

• 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

• Properties:– Hard– High melting point– Low conductivity (graphene is exception) 10

SiC in bulletproof vestsDiamond = carbon molecular solid

Ionic/Covalent Scale

• Electronegativity – How much an atom wants to gain electrons.

11Same electronegativity Very different electronegativity

Metallic Bonding

Atom cores

Sea of valence electrons

• Electrical Conductors

• Thermal Conductors

• Ductile materials

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Van der Waals forces• dipole-dipole• if between H & N, O, F

hydrogen bond

• dipole-induced dipole

• induced dipole-induced dipole (London Dispersion forces)

O

Intermolecular Forces

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H

H OH

H

OH

H

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Graphite• Intramolecular vs intermolecular

– Solid lines = covalent bonds = intramolecular foce

– Dotted lines = Van der Waals forces = intermolecular force

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.

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

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Source: Younan Xia, Washington University

Source: Seoul National University

Wires / Tubes

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Source: Evans Group, University of Leeds Source: Science Buzz, Science Museum of Minn.

• Electronics• Optics• Strength-based applications• Can characterize by aspect ratio

(length/(width or diameter))

Films, Layers, Coatings

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Surface is where all interactions and reactions take place.

Self-Assembled Monolayers: Ordered arrangement of

molecules that occurs spontaneously

tail

backbone

head

http://phys.org/news85328131.html#nRlv

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?

• Observe color visually• Observe color with

spectrometer

http://www.cytodiagnostics.com/store/pc/Gold-Nanoparticle-Properties-d2.htm

Dalton Trans., 2014,43, 5054-5061