SUMMARY - Descriptions METALLIC Strong malleable solids Don’t dissolve eg copper IONS ONLY IONIC Crystals Dissolve in water eg sodium chloride (salt) IONS + FREE ELECTRONS SIMPLE MOLECULAR Usually Gases eg CO2, H2O ATOMS joined into GIANT MOLECULES GIANT MOLECULAR Hard strong solids Don’t dissolve eg diamond (graphite – special case) MOLECULES ONLY

SUMMARY - PROPERTIES Structure Property Reason Ionic HIGH mpt/bpt CONDUCT: Solid NO Molten YES Dissolved YES Strong bonds between IONS Ions can’t move Ions can move to carry current Covalent – Simple molecular LOW mpt/ bpt (often gas at room temp). Soft when solid CONDUCT: Never Bonds between MOLECULES very weak. Molecules aren’t charged Covalent – giant molecular HIGH mpt/bpt. Hard & strong Strong bonds between all ATOMS No free charges/electrons Covalent - graphite Soft & slippery CONDUCT: YES (fairly well) Strong bonds between ATOMS Weak bonds between LAYERS Free electrons between layers Metallic Malleable CONDUCT: YES (very well) Regular structure, layers slide Free electrons between ions

Structure of an Alloy Draw this picture. What 2 things are obvious from it? Different size atoms Irregular structure This makes alloys HARDER than pure metals.

Smart Materials Smart materials' 'are materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields.

Smart Liquids When a magnetic field is applied to the fluid it becomes semi-solid and when the field is removed, the fluid returns to a free-flowing liquid. http://www.youtube.com/watch?v=kL8R8SfuXp8

Shape Memory Alloys A shape memory alloy is an alloy that "remembers" its original, cold, forged shape, and which returns to that shape after being deformed by applying heat. http://www.youtube.com/watch?v=fsBHF_j2FJ4

Exam Question

Nanomaterials Are very small but how small?

Human hair 9 micrometers is equivalent to 0.000009 m 40 microns 9 microns

Very Small Can Make Properites Very Different 0.000000009 m is 9 nm or 0.009 micrometers 0.25 nanometers is the average length of a bond between atoms!!! Very Small Can Make Properites Very Different

Some Potential Uses Filtration Catalysis Tissue engineering Drug delivery Diagnostics Memory storage Quantum computers Optoelectronics

Quantum dots

Nanotubes Cylindrical carbon molecules have novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential uses in architectural fields. They exhibit extraordinary strength and unique electrical properties, and are efficient thermal conductors. Their final usage, however, may be limited by their potential toxicity and controlling their property changes in response to chemical treatment.