The Atom’s Family – Part 2

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

2. Key Concepts: Fireworks • Fireworks 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. Prof. Lynn Cominsky

3. More Questions about Metals • What materials make the best magnets? • Where are they located on the periodic table? Prof. Lynn Cominsky

4. Iron Lodestone (Magnetite) 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. Prof. Lynn Cominsky

5. 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. Prof. Lynn Cominsky

6. 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? Prof. Lynn Cominsky

7. First activity: making magnets • Given: Magnets of various sizes and shapes, boxes of paper clips, long iron rods,hammers • Try to magnetize the paperclips by holding them next to magnets • Then put them in a box and shake them to demagnetize • Try magnetizing the iron rod and then hitting it with a hammer to demagnetize Prof. Lynn Cominsky

8. Key concepts: magnets • Since electron spins can have two different orientations, this leads to two different types of magnetic poles • If 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 flip • Magnetism is not easy to understand using the orbital model. Fe, Co and Ni make good magnets, but Mn does not. Prof. Lynn Cominsky

9. 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! Prof. Lynn Cominsky

10. S N Vocabulary • Magnet: material that can both attract and repel other magnets. Iron is most common. • Pole: Part of the magnet where the force is the strongest • Metal: material that is often attracted to magnets and a good electrical conductor Prof. Lynn Cominsky

11. 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? Prof. Lynn Cominsky

12. 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 Prof. Lynn Cominsky

13. Break – Thinking about magnets • Is it true that all magnets have exactly two poles? • Are the poles of equal strength? Prof. Lynn Cominsky

14. 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? Prof. Lynn Cominsky

15. 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. Prof. Lynn Cominsky

16. Isotopes: Thinking Deeper • This plot of proton number vs. neutron number shows the stable nuclei. Prof. Lynn Cominsky

17. Alphas, Betas and Gammas • Alpha particlesare doubly ionized Helium nuclei4He++ • 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 Prof. Lynn Cominsky

18. Radioactive Decay • The 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 emission • Beta emission (either e+ or e-) • Electron capture Prof. Lynn Cominsky

19. Alpha emission • Decay produces an alpha particle • Resulting nucleus has –2p and –2n. • Gamma-rays are usually emitted also. Prof. Lynn Cominsky

20. Beta emission (e-) • Electrons are emitted by beta decay in which: n  p + e- + n Prof. Lynn Cominsky

21. Beta emission (e+) • Positrons are emitted by beta decay in which: p  n + e+ + n Prof. Lynn Cominsky

22. Electron capture • Electrons are captured by protons, creating neutrons • p + e-  n + n Prof. Lynn Cominsky

23. 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 Prof. Lynn Cominsky

24. 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? Prof. Lynn Cominsky

25. 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? Prof. Lynn Cominsky

26. Second activity: Half life of pennies • Given: shoebox with lid containing 100 pennies, all tails up • Hold 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. Prof. Lynn Cominsky

27. 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? Prof. Lynn Cominsky

28. 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 Prof. Lynn Cominsky

29. 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. Prof. Lynn Cominsky

30. 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 Prof. Lynn Cominsky

31. Publisher’s Materials • Take some time to look through the state-adopted texts to find activities relating to isotopes and elements. Prof. Lynn Cominsky

32. 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? Prof. Lynn Cominsky

33. 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- + n • Half-life of 14C is 5730 years Prof. Lynn Cominsky

34. 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. Prof. Lynn Cominsky

35. 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 Prof. Lynn Cominsky

36. 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. Prof. Lynn Cominsky

37. 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? Prof. Lynn Cominsky

38. 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? Prof. Lynn Cominsky

39. Break – thinking about radioactivity • What do you think is the most common source of naturally occurring radioactivity? ? Prof. Lynn Cominsky

40. 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. Prof. Lynn Cominsky

41. 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. Prof. Lynn Cominsky

42. Key Concepts: Semiconductors • With 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. Silicon – moderate conduction Glass – good insulation Copper – good conduction Prof. Lynn Cominsky

43. Key Concepts: Semiconductors • Silicon 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. Prof. Lynn Cominsky

44. Key Concepts: Semiconductors • The 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. Prof. Lynn Cominsky

45. Key Concepts: Semiconductors • In 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. Prof. Lynn Cominsky

46. Key Concepts: Semiconductors Prof. Lynn Cominsky

47. Fourth Activity: Exploring Semiconductors • Given: light source, solar cell, wires, little motors • Two 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? Prof. Lynn Cominsky

48. 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? Prof. Lynn Cominsky

49. 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? Prof. Lynn Cominsky

50. 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. Prof. Lynn Cominsky