CHEM 120 Chapter Notes - Chapter 3: Shortwave Radio, Photon, Atomic Orbital

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24 Dec 2015

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Size of atom depends on its electrons. Electrons determine many of the chemical and physical properties of atoms. Quantum absolutely small; how electrons are described. Quantum particles (like electrons) can be in two different states at the same time. Ex. during radioactive decay an atom can emit absolutely small energetic particles from its nucleus and not editing particles at the same time. Quantum mechanical model - a model that explains the strange behavior of electrons. the model describes electrons as they exist within atoms, and those electrons determine the chemical and physical properties of of elements. Light has many characteristics in common with electrons. Main characteristic is common was the wave-particle duality of light. Certain properties of light are best described as a wave while others are as particles. Light is electromagnetic radiation a type of energy embedded in oscillating electric and magnetic elds. Magnetic eld: region of space where a magnetic particle experiences a force.

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Please help me finish lab...my lab stopped working and I can'tget the labs to finish. I highlighted and underlined my answers. Ibolded the questions that I could not finish.

1-4: Investigating the Properties of Alpha and BetaParticles

As scientists began investigating the properties of atoms, theirfirst discovery was that they could extract

negatively charged particles. They called these particleselectrons, but they are also known as beta

particles in the context of nuclear decay. Robert Millikan usedbeta particles in his famous Oil Drop

Experiment. Another particle ejected during nuclear decay is thealpha particle. An alpha particle is a

helium nucleus, or a helium atom without its two electrons.Consequently, an alpha particle is positively

charged. Ernest Rutherford used alpha particles in his Gold FoilExperiment.

1. Start Virtual ChemLab and select Alpha and BetaParticles from the list of assignments. The lab will open inthe Quantum laboratory.

2. What source is used in this experiment? Drag yourcursor over the source to identify it.

ElectronGun

What type of charge do electrons have? Negative

What detector is used in this experiment? A phosporScreen

3. Turn on the Phosphor Screen. (Click on the green/redbutton.)

What do you observe? A dot in the center of thescreen

The phosphor screen detects charged particles (such aselectrons) and it glows momentarily at the positions where theparticles impact the screen.

4. Drag the lab window down and left and the phosphor screenwindow up and right in order to

minimize the overlap. Push the Gridbutton on the phosphor screen, and set the Magnetic Fieldto 30

?T. (Click the button above the tens place three times. If youmistakenly click between digits, it will

move the decimal point. Click it to place it where it wasoriginally and then click above the tens

place.)

What happens to the spot from the electron gun on thephosphor screen? the dot moves to theright

5. Click once above the tens place on the ElectricField meter. Observe the spot. Click a second time

above the tens place on the Electric Field.

What happens to the spot from the electron gun on thephosphor screen? The dot moves to theleft

6. Zero out the Magnetic Field and ElectricField meters by clicking on the appropriate digit buttonsuntil the spot on the phosphor screen is centered again.

7. Double-click or click and drag the electron gun to move it tothe Stockroom counter. Enter the Stockroom byclicking inside the Stockroom. Double-click the electrongun to move it back to the shelf. Double-click on the alpha sourceto select it and move it to the Stockroom counter. Clickon the green Return to Lab arrow to return to the lab.Drag the alpha source from the Stockroom counter and placeit on the table where the electron gun was originally placed (themiddle spot light). Click on the front of the alpha source to openthe shutter.

What appears on thephosphor screen?

Atomic Theory

8. Change the unit for the Magnetic Field from ?T to mTby clicking once above the unit. Click above the hundreds placethree times to set the Magnetic Field to 300 mT(millitesla). This magnetic field is one million times strongerthan what we used for the electron gun.

Whichdirection is the spot deflected when the magnetic field isincreased this time?

How doesthis compare with the direction of movement when the magnetic fieldwas turned on for the electrons?

9. Change the unit for the Electric Field from V to kVby clicking once above the unit. Observe the spot as you increasethe Electric Field strength from 0 kV to 5 kV. Themovement is slight so pay careful attention.

Whichdirection is the spot moved when you increase the ElectricField?

How doesthis compare with the direction of movement for the electron beamin the Electric Field?

Why does ittake significantly stronger magnetic and electric field strengthsto move the beam of alpha particles compared with the beam ofelectrons (beta particles)?

10. Return the values on the two meters to zero. Double-click(or click and drag) the alpha source and the phosphor screen toreturn them to the Stockroom counter. Enter theStockroom. Double-click on the alpha source and thephosphor screen to place them on the shelf. Select the laser andthe video camera by double-clicking on them, and then click on thegreen Return to Lab arrow to return to the lab. Place thelaser in the center spotlight on the left and turn the laser on(click on the red/green light). Place the video camera on thecenter spotlight on the right and click the video camera to turn iton. Set the laser intensity to 1 nW and the wavelength to 20 nm.This wavelength is in the x-ray region of the electromagneticspectrum. The purple dot is a representation of the x-rays hittingthe video camera. Change the Electric Field andMagnetic Field to determine the effect on the x-rays.

Did theelectric or magnetic fields affect the x-rays? Why or whynot?

Summarizewhat you have learned about electrons (beta particles), alphaparticles, and x-rays.

he Aurora Borealis is caused by emission in the upper atmosphere from atoms, molecules, and ions excited by high energy particles originating from the sun. One of the strongest emissions is due to a single extremely narrow wavelength (557.7 nm) from very energetic oxygen atoms decaying to a lower, but still excited energy level. The transition is 1S to 1D and is not allowed (âforbiddenâ) by the quantum selection rules for electric and magnetic dipole transitions. The consequences are a very low transition probability, slow decay and very narrow band radiation. The radiative lifetime of the excited atoms is about a second â an eternity by ordinary electronic transition standards. In that time, at normal pressures, many of the excited atoms lose their energy nonradiatively by collisions with other atoms and molecules. The green radiation is only possible in the near vacuum of the upper atmosphere where collisions are less frequent. Oxygen atoms are also responsible for red aurorae. If oxygenâs green radiation is emitted grudgingly, its red light is even more so. The radiation is from atoms at a lower excited state, the 1D state, decaying to the ground (3P). This transition is also forbidden; the radiative lifetime is an immense 110 seconds and the atoms only have a chance to radiate above 150 km. At lower altitudes their energy is lost in collisions. We only see aurorae because we are looking through tens to hundreds of kilometres of glowing gas. By sea level standards that âgasâ is actually a vacuum. At 100 km, the altitude of green aurorae, the atmosphere's pressure is a millionth of that at sea level and the mean distance an oxygen atom travels between collisions is about a meter. Even so, it undergoes about 500 collisions each second and most excitation is removed nonradiatively. Only a small fraction of the 1S oxygen atoms radiate but this is enough to be observed. At 200 km, where the red oxygen aurora glows, the pressure is even lower. An oxygen atom will travel on average 4 to 5 kilometers between collisions and will be hit on average only once every 7 seconds. Even oxygen atoms in the 1D state have enough time to radiate their energy, and their collective light over a layer perhaps tens of kilometers thick gives us the soft and elusive auroral glow. Lights in a vacuum.. ..almost!

a) What are the possible term symbols for a p2 configuration?

b) Explain why the two transitions discussed above are forbidden: 1S --> 1D and 1D --> 3P (Which selection rules given in Eq. 9.46 are disobeyed?)

c) Draw a rough energy level diagram using the information in the table. Use arrows to show the transitions described above and calculate the transition wavenumber and wavelength. Do your results explain the colors observed in the Aurora Borealis?

State	/cm^-1
³P₂	0
³P₁	158.265
³P₀	226.977
¹D₂	15867.862
¹S₀	33792.583

Plastics Identification Data Table
Letter Label	Sampleâs Color	Sampleâs Shape	Floats in Water? (Yes/No)	Sinkersâ Boiling Water Results (Note color/shape changes.)	Sinkersâ Acetone Test Results (Note texture changes.)	Floatersâ Alcohol Test Results (Note number of squirts.)	Plastic Type
A
B
C
D
E
F
G

Questions

Why does PP float before HDPE and LDPE in the alcoholâwater solution?

Did any of the four plastics melt in boiling water? (Hint: How does melting differ from softening in plastics?)

When PS reacts with acetone, is this a physical or chemical change? Explain.

What is the approximate density of the alcoholâwater solution that was diluted with water to help identify LDPE from HDPE?

Looking at plastic containers like milk jugs, deli boxes, detergent bottles, soda bottles, and pill vials makes a person wonder whether they are really all that different from one another. The numbers and letters in the recycle codes seem to indicate that the plastics arenât the same, because these codes all refer to different kinds of plastics. For example, HDPE (high-density polyethylene) has the plastics recycling code number 2, while number 3 is used for PVC or V (polyvinyl chloride). An example of the polyethylene terephthalate (PETE) recycle code is shown at right. In this Activity, you will follow a flowchart to determine the identity of all seven recyclable plastics, without their labels; the first separation involves comparing the densities of plastic pieces to water.

A recycling plant may use manual separation of containers by having people visually recognize and remove containers as they travel along a conveyor belt. All of one kind of plastic will be collected at one location in the plant. Automated sorting may use whole containers or cut-up containers, called flake. Flake sorting involves putting the flakes into large containers of water to separate the âfloatersâ from the âsinkersâ. Whole container sorting uses electromagnetic radiation such as visible, near infrared, and X-ray systems. Optical sorting uses visible light to sort containers by color. Containers exposed to near infrared light absorb specific wavelengths and transmit others based on crystallinity of the plastics. Sensors detect the change in wavelength for each container and initiate the sorting by using jets of air to blast a container to a specific location. X-ray systems detect chlorine atoms in PVC. Recycle plants may sort plastics by using a combination of the systems described above or other technologies that are currently being developed.

Try This

You will need: seven kinds of plastic containers with different recycle codes, scissors, two cups or beakers, two stirring rods or wooden craft sticks, room temperature water, 70% isopropyl alcohol, graduated cylinder, acetone, 2 plastic pipets, hot plate with a 400 mL beaker of boiling water (student groups may share the boiling water), tongs, and forceps.

Cut a small, flat piece (1.5 cm Â´ 1.5 cm) from each container (seven total) and start a data table to record the color and shape of each piece as well as the permanent marker letter label (AâG) your instructor previously marked on each container. If two containers are the same color, cut different shapes (triangle, rectangle, circle, etc.) to help with piece identification. Now you are ready to follow the flowchart. Record your observations in the data table as you go along.

Tap Water Test: Place all seven pieces of plastic in a beaker or cup of room temperature tap water. Stir vigorously with a stirring rod or wooden craft stick to dislodge any bubbles from the plastic pieces. Bubbles tend to adhere to plastics. How would this change the apparent density? Observe and record which pieces sink and which float.

70% Alcohol Test: Remove the pieces that float from the water. Add them to a beaker or cup containing about 20 mL of 70% isopropyl alcohol. Stir. Do the pieces sink or float in the 70% alcohol? How does the density of alcohol compare to water?

Using a plastic pipet, add a squirt of tap water to the beaker containing alcohol. Stir. Do any of the pieces begin to float? When adding water to 70% alcohol, how does the density of the solution change? Keep adding squirts of water and stir until one piece floats. According to the flowchart, what is the identity of this plastic? Remove the piece and record your results.

Add more squirts of water until a second piece floats. Remove the piece and record the identity of the second plastic. You can now identify the third piece since it is still sinking.

Boiling Water Test: Place the four pieces that sank in tap water in the beaker of boiling water for a minimum of 30 s. Using tongs, remove them one at a time and test their flexibility, noting their size and color. Record your results. Which plastics can you now identify using the flowchart?

Acetone Test: Place the final two plastic samples in a small amount of acetone for one minute. Record your results.

Check with your instructor to see whether you correctly identified the seven plastics. You are now ready for an unknown. If your unknown floats in the tap water test, you will need to use the known pieces for PP, HDPE, and LDPE along with your unknown to help you with the identification in the 70% alcohol test.

More Things To Try

You might want to explore plastics coded as 7, âotherâ, or âmixedâ with this approach (see the figure at right). The results may be inconclusive because two or more polymers may be used to make these containers, or it might be 95% of one plastic and 5% another so that it will test as one component. Some containers have many additives to give the container a softer texture; some have several coloring agents. These additives will alter the density of the plastic. Another experiment to try is to test whether black microwavable PET dinner trays react like the transparent PET bottles.

CHEM 120 Chapter Notes - Chapter 3: Shortwave Radio, Photon, Atomic Orbital

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