Init 3/1/2011 by Daniel Raymond Barnes

... explain how salt dissolves in water... explain why some materials conduct electricity and others don’t.... explain diffusion

conductor insulator

At present, this power point is just a bare bones outline. I will flesh it out with pictures and animations when time permits.

Diffusion: use drop of food coloring in beaker to show effect of random molecular motion. This helps explain the dissolving process, which helps explain why salt water conducts electricity.

Covalent vs Metallic bonds: compare & contrast water molecule with chunk of iron. They both involve sharing of electrons, but only in the metal are the shared electrons allowed to wander all over the place, hence, its conductivity. Molecular motion in still air vs. Molecular motion in windy air vs. Molecular motion in still water vs. Molecular motion in water in a current vs. Electron motion in non-conducting metal vs. Electron motion in conducting metal. Balance vs. Bias. Voltage drives electric current.

Testing of samples for conductivity, pt I (solids only): 1.Screwdriver shaft (This this thing provide energy? No. Just a path for the flow of electron traffic. It’s the road, not the gasoline.) 2. Screwdriver handle 3.Aluminum foil 4.Plastic spoon 5.Glass beaker 6.Washcloth 7. Wooden ruler Routing of electron flow through conductivity apparatus, including *discussion of plastic insulation vs copper wire (protecting humans from electrocution AND protecting house wiring from shorts) *light bulb interlude (button, black donut, collar, W filament) *irony of carbon, a “nonmetal”, being a conductor.

Testing of samples for conductivity, pt II: 1. Tap water 2. Distilled water 3. Salt (cr) 4. Salt water (salt + distilled water) 5. Sugar water (sugar + distilled water) 6. Vinegar 7. Ammonia (aq) 8. Oil 9. HCl

Q1: What are particles doing when a metal is conducting electrical current?

Al 3+

Q1: What are particles doing when a metal is conducting electrical current? Positive metallic ions are stuck in place, in a crystal pattern, due to metallic bonding. Metallic cations may be stuck in place, but electrons are free to wander. When electric current is flowing, Positive and negative charges move relative to one another. (A car moves relative to the road, even though the road is not moving relative to the earth.) When a voltage is applied, electron wandering becomes imbalanced.

Q2: Why did the insulators not conduct? Insulators tend to be made of nonmetal elements. For instance, plastics, like wire insulation, are made of carbon and hydrogen. Nonmetal atoms have high electronegativities & high ionization energies, so they don’t allow their electrons to wander. Electrons on a nonmetal atom stay home, orbiting their nucleus.

Q3: What are the particles doing when an electrolyte solution is conducting current?

Na + Cl - Na Cl Na + Cl -

Na + Cl - Na Cl Na + Cl -

Na + Cl - Na Cl Na + Cl -

Q3: What are the particles doing when an electrolyte solution is conducting current? An electrolyte solution includes positive and negative ions wandering around in the solvent. (The solvent is usually water, so most electrolyte solutions are “aqueous” solutions.) The positive electrode can pull electrons off of negative ions. Such electrons then travel through the wires and light bulbs, making the light bulbs light up. The electrons then are given away by the negative electrode to positive ions.

electronegativity

Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl -

Explanation of how water dissolves the ionic and polar materials that it does dissolve. Invocation of polarity of covalent bond between H & O in H2O. + - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na +

Idea of an “electrolyte” as a substance that breaks into ions in water. Comparisson of acetic acid vs. hydrochloric acid: Weak molecules are strong electrolytes/strong acids. Strong molecules are weak electrolytes/weak acids. Show dissociation equations. HCl has single arrow, CH3COOH has double arrow. NaCl(cr)  Na + (aq) + Cl - (aq) HCl(g) + H 2 O(l)  H 3 O + (aq) + Cl - (aq) CH 3 COOH(aq) ↔ CH 3 COO - (aq) + H + (aq) STRONG electrolyte weak electrolyte