Download - The Atom’s Family – Part 2 NBSP Physical Sciences Leadership Institute July 7, 2003 Professor Lynn Cominsky Joanne del Corral Sharon Janulaw Michelle Curtis.

The Atom’s Family – Part 2

NBSP Physical Sciences Leadership Institute

July 7, 2003

Professor Lynn Cominsky

Joanne del Corral

Sharon Janulaw

Michelle Curtis

7/7/2003 Prof. Lynn Cominsky 2

Key Concepts: FireworksFireworks make colors through two different physical processes: Incandescence: different elements burn at

different temperatures – these temperature differences are manifested as different colors of light. For example, a blue flame is hotter than orange

Luminescence: electrons jump up to higher energy levels, releasing different colored photons when they fall back down

For more, see the handouts in your binders.


More Questions about Metals

What materials make the best magnets?

Where are they located on the periodic table?


Magnetic elements: A deeper look

Spinning electrons can act as magnets In Iron, it is easier to make the electrons

line up than in other materials. When electron spins line up, they make a stronger magnet.

Iron

Lodestone (Magnetite)


Magnets: Thinking deeper

Which elements make the best magnets? We want to have orbitals that contain

unpaired electron spins. Then all the spins can line up together to make a stronger magnet.

Iron has filled shells for 1s, 2s, 3s and 4s. But for the 3d shell, it has 4 unpaired electrons. These are the ones whose spins line up to make iron a good magnet.


Magnets: Thinking deeper

In most materials, if you add energy to the electrons, you can get them to move and realign their spins

Can you think of ways to add energy to electrons?

How can you make a magnet? How can you demagnetize a magnet?


First activity: making magnets

Given: Magnets of various sizes and shapes, boxes of paper clips, long iron rods,hammersTry to magnetize the paperclips by holding them next to magnetsThen put them in a box and shake them to demagnetizeTry magnetizing the iron rod and then hitting it with a hammer to demagnetize


Key concepts: magnets

Since electron spins can have two different orientations, this leads to two different types of magnetic polesIf you add energy, it is easier to magnetize or demagnetize a metal, as you are giving the electron’s enough energy to cause the spins to flipMagnetism is not easy to understand using the orbital model. Fe, Co and Ni make good magnets, but Mn does not.


Key concepts: magnets

Some of the strongest magnets are made of rare earth elements like Neodymium (Nd), combined with Fe and B. (Nd2Fe14B)

Magnetic strength is measured in Gauss.

The Earth’s magnetic field is about 0.5 G. A Nd2Fe14B magnet can be 12,000 G!


Vocabulary

Magnet: material that can both attract and Magnet: material that can both attract and repel other magnets. Iron is most common.repel other magnets. Iron is most common.

Pole: Part of the magnet where the force is Pole: Part of the magnet where the force is the strongestthe strongest

Metal: material that is often attracted to Metal: material that is often attracted to magnets and a good electrical conductormagnets and a good electrical conductor

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ELD Activities: Comparing objects

Take a cylindrical or bar magnet around your house and try sticking it to different things. First predict whether or not the magnet will stick to the object. Then fill in the table below with the names of the things you have tested and write the result.

What are the objects made of?

Object Prediction/Result Made from?


Publisher’s Materials

Take some time to look through the state-adopted texts to find activities relating to magnets that could be used in your classroom.

Example: HC p. C44


Break – Thinking about magnets

Is it true that all magnets have exactly two poles?

Are the poles of equal strength?


Standard Connections

Students know each element has a specific number of protons in the nucleus (the atomic number) and each isotope of the element has a different but specific number of neutrons in the nucleus (8)

What are the names of the two isotopes of Hydrogen that appear on the earlier slides? How many neutrons do they have?


Isotopes: Thinking Deeper

Most of the lighter stable elements have about the same number of protons as neutrons in the nucleus.As the number of protons in the nucleus increases, it is harder for the strong force to overcome the electrostatic repulsion of the positive charges. In order for the nucleus to remain stable, an even greater number of neutrons are needed to shield the protons. However, too many neutrons also makes a nucleus unstable.


Isotopes: Thinking Deeper

This plot of proton number vs. neutron number shows the stable nuclei.


Alphas, Betas and Gammas

Alpha particles are doubly ionized Helium nuclei 4He++

Beta particles are either electrons (e-) or their anti-particles, positrons (e+)

Gamma rays are the most energetic type of light – they are not particles at all!

Alphas, beta and gammas are often emitted by radioactive decay of unstable nuclei


Radioactive DecayThe weak nuclear force is responsible for radioactive decay. Different types of reactions can yield alphas, betas or gammas as well as other elementary particles called neutrinos (“little neutral ones”)Alpha emissionBeta emission (either e+ or e-)Electron capture


Alpha emission

Decay produces an alpha particleResulting nucleus has –2p and –2n.Gamma-rays are usually emitted also.


Beta emission (e-)

Electrons are emitted by beta decay in which:

n p + e- +


Beta emission (e+)

Positrons are emitted by beta decay in which:

p n + e+ +


Electron capture

Electrons are captured by protons, creating neutrons p + e- n +


Radioactive Decay

There are no stable nuclei with Z>83

What element has Z=82?

Unstable nuclei decay in a chain of reactions until they reach a stable nucleus

Each reaction has a different rate, characterized by a half-life the time it takes for half of the radioactive nuclei in a sample to turn into a different element


Math Connections: Radioactive Decay

Given: 10 g of 32P – radioactive Phosphorus, with a half-life of 14 days

How much is left after 14 d? 28 d? 42 d?


Math Connections: Radioactive Decay

32P becomes 32S after the decay. What type of decay was it? (Z=15 for P, Z=16 for S)

How much 32S is formed after 14 d? 28 d? 42 d?


Second activity: Half life of pennies

Given: shoebox with lid containing 100 pennies, all tails upHold the lid on, and shake the box up and down sharply, once.Open the lid, count how many pennies have become heads. Write the number in your data notebook in a table. Remove them.Repeat until all the pennies have turned into heads and have been removed.


Second activity: Half life of pennies

Graph the number of remaining coins (y-axis) vs. the number of shakes (x-axis).What is the half-life of the pennies?


Vocabulary

Isotope: elemental form with different number of neutrons

Radioactive: element that spontaneously emits charged particles or light

Alpha-particle: ionized Helium nucleus

Beta-particle: electron or positron

Gamma-ray: energetic form of light

Half-life: time it takes for half the element to radioactively decay


ELD Activities: Academic Language

There are many other examples in the English language that use Greek letters. Can you think of any?What is the difference between radioactivity and radiation?Write in your native language a definition of radioactivity and radiation, then write the definition in the language being learned.


ELD Activities: Involving Parents

Provide a bilingual handout that the child can share with his/her parents.

If you don’t speak the native language of the ELL, use any resource you can, in this case the child’s parents.

You may also have bilingual students in your classroom who can work with the ELL students. Chances are one of your co-workers can help you with the translation



Take some time to look through the state-adopted texts to find activities relating to isotopes and elements.


Lunch: Some things to think about

Is all radioactivity dangerous?

How much naturally-occurring radiation do you think you are exposed to on a yearly basis?

How much radiation are you exposed to during a dental X-ray? How does it compare to your average yearly dose?

How much more radiation do you get if you: Fly in airplanes regularly? Live in Denver?


Carbon-14 dating

14N + cosmic ray particle 14C

Carbon in atmosphere forms CO2

All living things take in CO2 until death

After death, 14C 14N + e- + Half-life of 14C is 5730 years


Radioactivity: The numbers

In the United States, the annual estimated average effective dose equivalent from radiation is 360 mrem per adult.

82% of the total average annual effective dose is from natural sources of radiation

Of the other 18%, the majority is from medical diagnosis and treatments, with <1% from nuclear power and fallout.


Radioactivity: The numbers

Airplanes: Add 1 mrem for each 1000 miles traveled in jets

Denver: Living at 5000 feet and in the Colorado Plateau adds about 70 mrem each year to your total dose

For more, try the EPA dose calculator: http://www.epa.gov/radiation/students/calculate.html


Third Activity: Radioactivity

Given: 6 computer stations set up with radioactive sources and Geiger counter, and one with background.Record in your lab book the background radiation count (15 sec sampling intervals)At each of three stations; alpha, beta and gamma, record the 15 sec count rate for the following 4 conditions: unshielded, covered with thick paper, covered with 3 mm plastic, covered with 3 mm lead.


Radioactivity (continued)

Make a table to display the fractional decrease in count rate for each sample for each condition.For each type of radiation were you able to decrease the count rate so that it was similar to the background count? What did it take?Which type of radiation was the easiest to block? Which type was the hardest? Were you able to totally block the gamma radiation with additional lead?


Radioactivity: thinking deeper

The Sentinel Node Dye test can be utilized in people diagnosed with breast cancer to determine involved lymph nodes.

The Dye contains radioactive technetium-99 injected into the body and the sensor is outside the body.

Based on what you have learned about radioactivity, what type of radiation do you think is being detected?


Break – thinking about radioactivity

What do you think is the most common source of naturally occurring radioactivity?

?


History:Semiconductors

Semiconducting materials were discovered and the transistor was invented in 1947 by Shockley, Bardeen, and Brattain. They received the Nobel prize in 1956 for their discovery.

Today transistors are very small and are packed onto small chips, called integrated circuits. Integrated circuits are the basis of all modern electronics and computers.


Review:Electrical Conductivity

We have seen that metals (especially copper, silver and gold) are good conductors. Electrons outside filled shells are free to move through wires made of these materials.

Plastics and glass do not conduct electricity at all – the electrons in these materials do not move even when large voltages are applied.


Key Concepts: SemiconductorsWith a semiconductor, the amount of conductivity can be controlled by the amount of voltage that is applied.This gives semiconducting materials the versatility needed for use in electronics and computer products.

Copper – good

conduction

Glass – good insulation

Silicon – moderate conduction


Key Concepts: SemiconductorsSilicon and Germanium are 2 elements commonly used as semiconductors.

A solid piece of pure silicon has a lattice structure with adjacent atoms sharing electrons in the outer shell.


Key Concepts: SemiconductorsThe highest energy electrons (the ones outside filled shells) are called valence electrons. In a solid, these electrons are in the valence band.The next higher (usually unfilled) shell is called the conduction shell. In a solid, it is known as the conduction band.There is a gap (“forbidden zone”) in energy between the valence and conduction bands.


Key Concepts: SemiconductorsIn a good conductor, there is room in the valence bands for more electrons. Conduction occurs when new electrons fill holes in the valence band, replacing electrons that are moving through the material.In an insulator, the valence band is filled, and the band gap is very large. It is hard to get any electrons into the conduction band.In a semiconductor, the valence band is filled, but the band gap is small. If a little bit of energy is applied, the valence electrons can jump to the conduction band.


Key Concepts: Semiconductors


Fourth Activity: Exploring Semiconductors

Given: light source, solar cell, wires, little motorsTwo solar cell units composed of semiconducting material are connected in series to obtain more voltage than just one alone. For them to be useful you must connect the wires from the cells to the small motor with fan attached.Now you have a current path. Does the fan turn?


Fourth Activity (cont)

Place the light source 50 cm away and turn it on. Aim it at the panels. What happens?If you look at the solar cell panels you will see small bumps in the protective covering. Do they remind you of small optical lenses? What might be their use?Bring your hand close to the light source. What is the relative temperature compared to the room? Warmer? Colder?


Fourth Activity: (cont)

If the protective cover is made of plastic, what would happen if you brought the light source too close?

If the fan did not move when when you turned on the light, on bring the light source closer.

Place it close enough to cause the motor to turn. Cover one panel with your hand. What happens?


Semiconductors: Things to think about

To turn on a light (rather than running the fan), greater current and voltage are needed, which can be obtained from connecting more solar panels.

Solar cells are just one use for semiconductors. From what you have observed, think of uses and limitations to solar panels in your home.


Vocabulary

Semiconductor: material that conducts electricity in some situations,but not in othersTransistor: small circuit made of semi-conducting material that can be used as either a switch or an amplifierIntegrated circuit: complex circuit made of hundreds (or more) transistorsValence: electron in highest energy level in an atom


ELD Activities: Compare

Survey your home or school to find all the electronic devices that contain integrated circuits.

Fill out the table below

Item Where Found Used for?


ELD Activities: Visual Imagery

Find pictures or examples ofConductors InsulatorsSemiconductors



Take some time to look through the state-adopted texts to find activities relating to silicon or other semiconducting elements


Lesson Study Activities

Identify a key concept from today’s lecture for further development

Review the publisher’s materials about this key concept

Think about the best way to present this key concept in your classroom


Take away - puzzler

Gallium is often used in conjunction with another element in semiconductors.

What other element would combine with Gallium so that the overall properties would be similar to Silicon or Germanium?


Resources

http://207.10.97.102/chemzone/lessons/11nuclear/nuclear.htm

http://particleadventure.orghttp://education.jlab.org/glossary/betadecay.html

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html#c6

http://education.jlab.org/glossary/electroncapture.htmlhttp://www.nobel.se/physics/educational/semiconductors/

http://www.carolina.com/chemistry/experiments/halflife2.asp

http://chemistry.about.com/library/weekly/aa062701a.htm

http://pubs.acs.org/cen/whatstuff/stuff/7927sci3.html

http://www.physics.isu.edu/radinf/natural.htm