Chapter 4 Nanomaterials & Bonding Introduction to Nanotechnology

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

Models of the Atom J.J. Thomson Rutherford Current model Proton Neutron Electron Charge Mass (kg) ~1.673*10-27 ~1.675*10-27 ~9.11*10-31 Location nucleus “clouds” Diameter of one atom: 0.1 – 0.5 nm (Carbon atom: 0.15 nm)

Covalent Bonding Minimum energy: Separation between atoms when bonded Attractive and repulsive forces cancel out Binding Energy Separation between atoms when bonded Interatomic distance Bond length Energy Interatomic Distance http://voh.chem.ucla.edu/vohtar/winter02/20A/lecture5.htm

Covalent Compounds Atoms share electrons to form molecules H + H H H Bonding electrons F + F F F F2 Lone pair electrons Covalent bonds usually between nonmetal + nonmetal

Ionic Bonding Forms salts Transfer of electrons Electrostatic attraction No sharing of electrons Non-Metal: Accepts electron Sodium Metal: Donates electrons Fluorine anion cation

Ionic solids Examples: NaCl (table salt), (NH₄)₂CO₃ Properties: High melting point Very hard Poor conductivity Water soluble 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) Diamond = carbon molecular solid SiC in bulletproof vests

Ionic/Covalent Scale Electronegativity – How much an atom wants to gain electrons. Same electronegativity Very different electronegativity

Sea of valence electrons Metallic Bonding Atom cores Sea of valence electrons Electrical Conductors Thermal Conductors Ductile materials

Intermolecular Forces Van der Waals forces dipole-dipole if between H & N, O, F hydrogen bond dipole-induced dipole induced dipole-induced dipole (London Dispersion forces) H O H H O O H H H All intermolecular forces are weaker than bonds (ionic, covalent, metallic)

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

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

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

Wires / Tubes Electronics Optics Strength-based applications 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 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

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

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

Gold NP Biosensors

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