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The Modern Quantum Description of the Atom What does the atom really look like? Do the electrons really orbit like the planets? No. The negative charge the electrons carry looks smeared out—or like a cloud. Another possible formation: (note: this is ONE electron) Other possible configurations (or symmetries) These symmetries are responsible for the symmetry in the bonding of solids! Summary: Atomic models Greek Jellium Planetary Bohr (Quantum) Modern Quantum Scientific Notation How do we write 1,000,000,000,000,000,000 in a more compact form? 1,000,000,000,000,000,000 There are 18 zeros We write this as 1 x 1018 How do we write 1,200,000,000,000,000,000? Again there are 18 spots after the first number, but we have to account for the 2. Answer: 1.2 x 1018 What is (1.82 x 1012) x (3.87 x 109)? Step 1: group the numbers as follows (1.82 x 3.87) x (1012 x 109) Step 2: multiply these: 7.04 Step 3: add the exponents of the 10’s: 21 Step 4: Write the result: 7.04 x 1021 What is (2.4 x 1020) / (1.6 x 1011)? Step 1: (Group) (2.4/1.6) x (1020 / 1011) Step 2: (Divide numbers): 1.5 Step 3: SUBTRACT exponents: 9 Step 4: Write in scientific notation 1.5 x 109 What is 0.0000000000005 in scientific notation? There are 13 digits. Thus we can write this as 5.0 x 10-13 What is (3.0 x 1012) x (2.0 x 10-4)? 6.0 x 108 What is (6.0 x 104) / (3.0 x 10-3)? 2.0 x 107 And now to use scientific notation … Charges Revisited  It comes it two types: positive and negative.  Charge is conserved.  Like charges repel; opposites attract.  It only comes in discrete amounts (the amount that comes with an electron). Materials: Conductors: materials where the electrons are free to move through the material. Examples include metals (like wires), salt water, etc. Insulators: Electron are NOT free to move through the material. Examples include rubber, plastic, wood, coatings on electrical cords, etc. Conductors Describe the forces between the two charges. + - Since unlike charges attract, the electrostatic force will try to pull them together. How will the charges MOVE if the material is an insulator? They will NOT move—the electrons can’t move in an insulating material. How will the charges move if + the material is a conductor? - They will move towards one another. + - Describe the force between two - negative charges placed in a - conducting material. Like charges repel so the two charges will repel one another. How will the charges MOVE? They will move away from one another. - - Where will the charges end up? - - A C - - - - B D - - - - WHY do the charges end up in this configuration?? They want to maximize the - - distance between them. Now suppose that we have a metal ball with two electrons in it. Where do the electrons go?? - - They should end up somewhere on the outer perimeter—this will maximize the distance - between them. - Now suppose that we add a third electron—where will the three of - them end up? - They will end up equidistant from each other, but at the same - time maximizing the distance from one another. What if there are FOUR charges? Again, the charges will configure - - themselves to maximize the distance from each of the other charges. The - - results in them being an equidistance apart. What if there are 1 x 1015 “free” electrons in a conductor—where do they end up? They end up spread out evenly on the SURFACE of the conducting material!!
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