1. The Atom
(Power Point 10)

2. Student Learning Objectives
Describe the structure of the atom and the resultant changes through fission, fusion, and radioactive decay.
Characterize the atom
Analyze the quantum nature of the atom
Analyze radioactive decay processes
Differentiate between nuclear fission & fusion

3. What are the defining properties of regular atoms?
Regular, neutral atoms have an equal number of electrons, protons, and neutrons.
What makes each atom unique is the number of protons.

4. Practice Where is most of the mass in an atom?
What contributes most to the size of an atom?
What is an ion?
Nucleus
Electron orbits
Electric force – electrons repelling
Electrons can be lost or gained

5. More Practice
Use your knowledge of what an ion is, to determine what an isotope is.
Since atoms are mostly empty space, why can’t we walk through walls?

6. What is meant by the wave-particle duality?
Quantum theory predicts that objects emit individual packets of energy (photons).
Sometimes light behaves as a wave (wavelengths) and sometimes light behaves as a particle (photons).
Wave-Particle Duality
Half way down link page

7. Wave-Particle Duality
All subatomic particles exhibit wave-particle duality.
Bohr postulated the electron is a particle orbiting the nucleus in specific orbits.
de Broglie contended that the behavior of electrons is explained only if the electron is considered as a standing wave.
Image Credit: Opentextbc.ca

8. Effects of Electron Standing Waves

9. de Broglie Wavelength ldB = h . mv
Every particle of mass creates a standing wave when in motion.
ldB = h . mv

10. Practice
How does the de Broglie wavelength of a person compare to the de Broglie wavelength of an electron?
Can we really know exactly where the electron is? Explain.
Mass
Speed
Electron (hydrogen)
9.1 x 10−31 kg
2.2 x 106 m/s
Person (walking)
70 kg
1.4 m/s

11. Heisenberg Uncertainty Principle
Heisenberg’s Principle: the position and the velocity of an object cannot both be measured exactly, at the same time.
Because of its wave character, a particle’s trajectory and destination cannot be precisely predicted for each particle individually.
Electron Probability Regions

12. How do atoms emit and absorb light?
Each atom has its own unique pattern of allowed orbits, based on the number of protons.
When electrons change orbits, light is emitted or absorbed.
Image Credit: Wikipedia

13. Image Credit: Openstax
Energy States
The farther an electron is from the nucleus, the higher its energy level.
Ground State: electrons occupy lowest energy levels
Excited State: electrons in added energy levels
Image Credit: Openstax

14. Each type of atom emits/absorbs its own specific pattern of photons.
Atomic Spectrum
Image Credit: Openstax

15. Photon Energy DEn = E(photon) E = hc l E = hn
Each photon has a particular energy, based on the quantum jump.
DEn = E(photon)
Each color of light has a particular energy per photon.
h = 6.63 x Js
E = hc l
E = hn

16. Practice
What is the energy of a photon that results from the 4  2 transition in the hydrogen atom?
What is this energy in Joules?
1 ev = 1.6 x 10−19 Joules
Hydrogen Orbit eV
n = 1 8
n = 2 15
n = 3 30
n = 4 80

17. More Practice
What is the energy of one yellow photon (l = 517 nm) from the Sun?
How does the energy of one photon from the Sun compare to the total energy output of the Sun (4 x 1026 Watts)?
Image Credit; NASA

18. How do we know the number of particles?
Atomic number = number of protons
Atomic Mass = mass in amu or grams
Mass number = protons + neutrons
178O−2

19. Practice
Classify each atom. Is it an ion? Is it an isotope?
32He
136C
3417Cl−1
5226Fe
63Li+1

20. How is the nucleus held together?
The protons and neutrons in the core of an atom are held together by the strong nuclear force.
Diameter < m
The strong nuclear force balances the electric force in a stable atom. FN FE

22. Nuclear Force vs. Electric Force
Strong Nuclear Force
Electric Force
Attraction
Repulsion
Protons & Neutrons
Protons
Range < m
Range > m

23. Practice
Would a helium (He) atom or a bismuth (Bi) atom tend to be more unstable?
Analyze the possible stability of a 32He atom.

24. 60+ radioactive elements found in nature
What is radioactivity?
Radioactivity is the transformation of an unstable atom into a different type of atom.
60+ radioactive elements found in nature
There are 3 general sources of radioactivity.
Earth
Cosmic Rays
Human Produced

25. Radioactive Decay processes
Atoms radioactively decay by emitting high energy particles.
If the decay particle comes from the nucleus, then the atomic number changes.
a decay (nucleus) b decay (nucleus) g decay (D e− orbit)

26. Can cause damage on the surface of matter
Alpha Decay
Alpha radiation (a) is the emission of two protons as a helium (He+) particle. The positively charged particle leaves the nucleus.
Can cause damage on the surface of matter
Image Credit: JAHSCHem - Wikispaces

27. Can penetrate through several millimeters of matter
Beta Decay
Beta radiation (b) is the emission of an electron (e−) with negative charge. A neutron splits, emits the electron, and leaves a proton.
Can penetrate through several millimeters of matter
83Li
84Be e−
Creative Commons Image

28. Can pass through all types of matter
Gamma ray
A Gamma ray (g) is a high energy photon that is emitted. An electron jumps from a very high orbit to a lower orbit.
Can pass through all types of matter
Excited
Atom
Same
Nucleus
Gamma Ray
released
Creative Commons Image

29. Creative Commons Image

30. The Rules Unstable Condition Name Symbol The Rules 83+ Protons Alpha+2 a
D(Mass #) = – 4
D(Atomic #) = – 2
Neutron/Proton Ratio
Beta e– –1 b
D(Mass #) = – 0
D(Atomic #) = + 1
Excited
Nucleus
Gamma
photon g
No Change

31. Practice Answer the listed questions for each nuclear reaction.
Is the atom an isotope?
What makes it unstable?
What is the resulting atom, X?
22688Ra  X + e−
22688Ra  X + a
22286Rn  X He
146C  X + b
3618Ar  X + g

32. What does the half-life of an element indicate?
Half-life is the time it takes for one half of an unstable substance to decay into a different substance.
The age of a sample can be determined from the number of half-life’s that have occurred.
Isotope
Half Life
156C
2.449 seconds
146C
5,730 years

33. Practice
An isotope of radium (Ra) has a half-life of 1620 years. If 1000 grams were placed in a barrel, how much of the material in the barrel would be radium after 6480 years?
22589Ac (Actinium) has a half-life of 10.0 days. How many days would it take to decrease the original amount placed in a barrel to 1/64th of the original amount?

34. More Practice
Caffeine has a half-life of 6 hours. If you drink an 8 oz (95 mg) cup of coffee, how long will it take for there be less than 12 milligrams remaining in your body?
A can of Mountain Dew has 56 mg of caffeine. How long would it take to have less than 12 milligrams of caffeine in your body after finishing this drink?

35. Carbon Dating
Carbon dating is the process of using the known half-life of carbon-14 to determine age of a sample.
Living plants and animals take in CO2 (Carbon-14)
Carbon-14 is a radioactive isotope
The half-life of carbon-14 is 5,730 years
146C  147N + b

36. Practice
The half-life of carbon-14 is 5,730 years. How old are the wood samples?
Sample has 1/2 the carbon-14 as a living tree
Sample has 1/4 the carbon-14 as a living tree
Sample has 1/32 the carbon-14 as a living tree
How do we know that the relative abundance of carbon-14 has been consistent for the last 50,000 years? Would this affect carbon dates of samples?

37. What is Nuclear Fission?
Nuclear fission is the splitting apart of a nucleus.
Electric force wins
Nucleus flies apart
Huge amounts of energy released
Nuclear fission is used in atomic bombs and nuclear reactors.
Atomic bombs produce a chain reaction.
Nuclear reactors control the rate of fission.

38. Uranium
Uranium fission yields 2.5 Million times more energy per gram than coal burning.
Creative Commons Image

39. Question
Nuclear energy is a clean fuel. It does not pollute the atmosphere. What reasons may people have for not wanting to utilize nuclear energy?
Diablo Canyons
Nuclear Power Plant
California

40. Proton-Proton Chain E = mc2
Hydrogen nuclei are forced together into helium.
Mass becomes energy.
E = mc2

41. 1 Second In The Sun
1038 Reactions 600 Billion kg H  He 4 Billion kg Mass  Energy 4 x 1026 Watts
Image Credit: NASA

42. Practice Compare and contrast nuclear fission and fusion.
Use the atomic mass to determine the amount of mass lost from the Sun in each PPC reaction.
How much energy would result from the nuclear fusion of a 5 gram grape?

43. Radiation Radiation is energy.
Decay particles may ionize and alter cells.
On average, Americans receive a radiation dose of about 0.62 rem (620 mrem) each year.

44. Some Common Radiation Sources
Dentist x-ray
1.5 mrems
Food
39 mrems
Electronics
11 mrems
Tobacco
1,300 – 9,000 mrems