CHEMISTRY CATALYSTS Fall 2011 – Week 7 (Nuclear & Electrons)

Catalyst (7 min)  9/19/11 Half-Lives  EQ: What is the half-life of a nuclear substance?  You have $12800 in your bank account. You spend half the money each month. How many months until you only have $25 left?  Show your work! $12800  $6400  $3200  $1600  $800  $400  $200  $100  $50  $

What is a half-life?  A half-life is the amount of time it takes for half of the amount of a substance to decay.  For example: 241 Pu has a half-life of 14 years. Suppose we start with 100 grams of 241 Pu 14 years later, we have 50 grams 28 years later, we have 25 grams 42 years later, we have 12.5 grams…  Band of Nuclear Stability & Half-Lives Band of Nuclear Stability & Half-Lives

Catalyst (5 min)  9/20/11 Fusion & Fission  EQ: What are fusion and fission?  The half-life of Rf-267 is 1.3 hours. How long will it be until only 1/128 th of the original amount is left?  Show your work.

Catalyst (5 min)  The half-life of Rf-267 is 1.3 hours. How long will it be until only 1/128 th of the original amount is left? 1/2  1/4  1/8  1/16  1/32  1/64  1/ half-lives x 1.3 hours = 9.1 hours

NUCLEAR FUSION & FISSION

Nuclear Reactions  Change the makeup of nuclei  Accompanied by the release of tremendous amounts of energy  Two types:  Nuclear fusion  Nuclear fission

Nuclear Fusion  two nuclei combine to form a heavier nucleus  releases large amounts of energy (fusion releases more than fission)

Nuclear Fusion  the sun (and all other stars) is a tremendous fusion reaction; the major fusion reaction in the sun is thought to be:

Nuclear Fission  A heavy nucleus splits into lighter nuclei

Nuclear Fission  some elements undergo fission spontaneously  some elements can be forced to undergo fission when bombarded with other particles (like neutrons)

Fusion or Fission? Does not occur in nature. Fission

Fusion or Fission? Two nuclei fuse to make a new nucleus. Fusion

Fusion or Fission? The nucleus of an atom fissures into new atoms. Fission

The Atomic Bomb (Fission)  when the nucleus of U-235 splits, 2 isotopes are formed, plus neutrons are emitted  these neutrons collide with other U-235 atoms, causing them to undergo fission; they release neutrons, and so on…  The result - CHAIN REACTION!!

The Atomic Bomb (Fission)

Nuclear Chain Reaction (Model) How is this video like a nuclear chain reaction?

 Little Boy was the first nuclear weapon used in warfare. It exploded approximately 1,800 feet over Hiroshima, Japan, on the morning of August 6, 1945, with a force equal to 13,000 tons of TNT. Immediate deaths were between 70,000 to 130,000. Atomic Bomb: Little Boy Little Boy was a uranium (U-235) device

 Fat Man was the 2 nd nuclear weapon used in warfare. Dropped on Nagasaki, Japan, on August 9, 1945, it was equal to 20,000 tons of TNT & devastated more than 2 miles of the city and caused about 45,000 immediate deaths. Atomic Bomb: Fat Man Fat Man was a plutonium (Pu-239) device

Atomic Bomb Tests (Nevada, 1955)

Nuclear Power Plants (Fission) *nuclear reactor *San Onofre, Ca Nuclear Generating Station. Use nuclear reactions to generate electricity

Nuclear Power Plants (Fission) 1. The energy released in the fission process generates heat, which can be converted into usable energy. 2. This heat is used to boil water to produce pressurized steam. 3. Steam turns turbine of a generator. 4. Generator makes electricity.

Nuclear Power Plants (Fission)

Pros of Nuclear Energy  no air pollution  enormous amount of energy is released compared to coal or oil  alternative to using our rapidly decreasing fossil fuels

Cons of Nuclear Energy  containers for waste products may erode or break (think half-life)  thermal pollution (heated water returned to rivers, etc.)  potential theft of fuel (Pu-239) for use in weapons

Fusion or Fission? Produces lots of radioactive particles. Fission

Fusion or Fission? Requires a very high temperature & high pressure environment. Fusion

Fusion or Fission? Is used to power nuclear power plants. Fission

Fusion or Fission? Releases the largest amount of energy. (3-4 times greater than the other) Fusion

Fusion or Fission? Can be used to trigger a fusion bomb (like a hydrogen bomb). Fission

Catalyst (5 min)  9/21/11 Nuclear Chemistry Wrap-up  EQ: What do you know about nuclear chemistry?  Write equations for the alpha, beta, and gamma decay of 264 Sg.  These will be graded for accuracy, so do your best work!

Catalyst (5 min)  9/22/11  EQ: What happens when atoms get excited?  Watch the video. 1. What creates rainbows? 2. What does this tell you about the color of light?  Science of Rainbows Science of Rainbows

How Do Rainbows Form? 1. White sunlight enters the drop of water. 2. The light bends as it enters causing it to split into colors. 3. The light reflects off the back of the drop of water. 4. The light bends more as it exits.

Plum Pudding Model JJ Thomson positive negative Nuclear Atom Ernest Rutherford Planetary Model Niels Bohr Modern Orbitals Erwin Schrödinger Flashback  Remember me?

Erwin Schrödinger  1926 – published a work describing the orbitals of an atom  Performed the double slit experiment  Schrödinger developed the wave particle duality of electrons. (Sometimes they behave like waves, sometimes like particles)

Double Slit Experiment Explained

Think About It What is light?

Frequency of Light High Energy Low Energy

Spectrum  A continuous spectrum contains all the colors of the rainbow in a connected band.  An atomic emission spectrum contains only colors specific to that atom in disconnected lines. Each one of these lines represents an electron dropping down from a specific energy level

Energy Levels of Hydrogen This is how Bohr studied Hydrogen

Atomic Orbitals  Bohr’s energy levels (orbits) were accurate for hydrogen, but they didn’t work for atoms with more than one electron.  Now we know that electrons don’t travel in circular orbits.  Electrons occupy a region around the nucleus called an orbital.

Emission Spectra

Electron Energy Level Diagram  Under normal conditions a hydrogen atom’s electron is in the lowest energy level, called the “Ground State” Ground State Excited State Energy e-e-

Electron Energy Level Diagram  When an atom absorbs energy, its electron can jump up to a higher energy level, further from the nucleus. Ground State (lowest energy) Excited State (higher energy) Energy e-e- Electricity or heat energy absorbed e-e-

Electron Energy Level Diagram  This excited state is temporary.  The electron will return to the ground state, emitting the ‘borrowed’ energy as colored light. Ground State Excited State Energy e-e-

Put it all together in your notes  Energy is absorbed & electron jumps to higher level  Energy is released as colored light when electron returns to ground state Ground State Excited State Energy e-e- e-e-

Flame Tests potassium lithium strontium calcium sodium Each element has a characteristic color when energy is added. neon

Spectrum  A continuous spectrum contains all the colors of the rainbow in a connected band.  An atomic emission spectrum contains only colors specific to that atom in disconnected lines. Each one of these lines represents an electron dropping down from a specific energy level

Catalyst (5 min)  9/23/11  EQ: What are the two types of atomic spectra?  Describe what happens when an electron in an atom gets excited.  Draw a diagram to show the process.

Spectroscope  A spectroscope is a tool used to measure the wavelength of light within the spectrum.  Our spectroscopes are qualitative (meaning they don’t give numbers, only colors)  Look through the hole and point the slit directly at your light source.

Diffraction Grating  A spectroscope uses a diffraction grating to separate white light into colors.  You have seen this before on the back of CDs and DVDs.

Emission vs. Continuous Spectra  An atomic emission spectrum (aka line spectrum) contains only colors specific to that atom in disconnected lines.  A continuous spectrum contains all the colors of the rainbow in a connected band.  For each of your lights, is it an example of an atomic emission spectrum or a continuous spectrum?

Your light sources are: 1. Incandescent bulb 2. Compact fluorescent bulb (CFL) 3. LED green holiday light 4. LED red holiday light 5. LED blue holiday light 6. LED orange holiday light 7. Incandescent white holiday lights 8. Incandescent bulb- red 9. Incandescent bulb- blue 10. Incandescent bulb- green 11. Plasma ball 12. Black light 13. Candle 14. Sunlight (if available)