Name:
Date:
Modern Physics
Models of the Atom
The word atom comes from the Greek word atomos meaning indivisible
We now know that this model of the atom is not accurate
JJ Thompson
Experiment and atomic model
Discovered the electron
Proposed “Plum Pudding” model of the atom”
Ernest Rutherford
Experiment & Changes to the Atomic Model
Gold foil experiment – shot alpha particles at thin gold foil barrier
Niels Bohr
Contribution to Atomic Model
Atomic emission & absorption spectra
Electrons can
only exist in
specific orbits
1
Atoms only
emit certain
colors of light
What is a photon?
Energy of a photon:
Ephoton =
1. A photon of light with a frequency of 6 x 1014 Hz is emitted from a light source. What is the energy
of the photon in Joules?
2. An electromagnetic wave with a wavelength of 1.5 x 10-8 meter is emitted from an atom. What is the
energy of the photon in Joules?
Application: Atomic Spectra
So what? Atoms can only absorb or emit photons with a
certain energy level.
Each energy corresponds with a certain frequency (or
color).
Hot gasses emit photons of a certain color
Cold gasses absorb photons of the same color.
Astronomers use this to determine the chemical
properties of distant stars and planets!
2
Energy Levels
When an electron changes energy
levels, it either gains or loses a
photon.
When an electron moves up in
energy, a photon is _____________
absorbed (gained)
When an electron moves down in
energy, a photon is ______________
emitted (lost)
________________________ is the
lowest energy level. The ground state
________________ occurs when an
electron is completely free from an
atom (highest energy level)
An electron can only exist at these energy levels, and not in between.
Energy of a photon:
Ephoton =
3. An electron in Hydrogen moves from its ground state to the n=3 state.
a. Is a photon absorbed or emitted by the atom?
b. Calculate the energy of the photon in eV.
c. Calculate the energy of the photon in J.
4. A photon with a wavelength of 2.29 x 10-7 meter strikes a mercury atom in the ground state.
a. Calculate the energy in Joules of the photon
b. Determine the energy in electron-volts of the photon
c. Based on your answer to the previous question, can this photon be absorbed by the mercury atom?
5. A hydrogen electron moves from the n=3 state to the ground state. This process emits a photon or
photons. How many possible photons can be emitted?
3
The Dual Nature of Light & Matter
Evidence that light is a wave
Evidence that light is a particle
Young’s Double Slit
Compton Scattering
Photoelectric Effect
Evidence that matter is a wave
Evidence that matter is a particle
Louis de Broglie
Why don’t we see the wave-nature of matter in everyday life?
6. Wave-particle duality is most apparent in analyzing the
motion of
1. a baseball
2. a space shuttle
3. a galaxy
4. an electron
9. On the atomic level, energy and matter exhibit the
characteristics of
1. particles, only
2. waves, only
3. neither particles nor waves
4. both particles and waves
7. Which phenomenon provides evidence that light has
a wave nature?
1. emission of light from an energy-level transition
in a hydrogen atom
2. diffraction of light passing through a narrow
opening
3. absorption of light by a black sheet of paper
4. reflection of light from a mirror
10. Which phenomenon best supports the theory that
matter has a wave nature?
1. electron momentum
2. electron diffraction
3. photon momentum
4. photon diffraction
8. Light demonstrates the characteristics of
1. particles, only
2. waves, only
3. both particles and waves
4. neither particles nor waves
11. Moving electrons are found to exhibit properties of
1. particles, only
2. waves, only
3. both particles and waves
4. neither particles nor waves
4
Conservation of Mass-Energy
E=
12. According to mass/energy equivalence, how much energy is stored in a 0.20 kg notebook?
13. In a chemical reaction, 242,000 Joules of energy are released. How much mass is converted to
energy in this reaction?
The Universal Mass Unit
14. How much energy, in megaelectronvolts, is produced when 0.350 universal mass unit of matter is
completely converted into energy?
15. In a nuclear reaction, 8.5MeV of energy is released. How many universal mass units does this
represent?
Pair Production When energy is converted into matter, charge is conserved
Charge is created in positive/negative pairs
Antiparticle same mass opposite charge of typical particle
Particle-Particle Annihilation When a particle meets its antiparticle, the two both
annihilate and become pure energy
16. An electron and a positron (the electron’s antiparticle) collide and both are annihilated as a result.
How much energy is created in this collision?
17. How much energy would be required to create 3 protons and 3 anti-protons?
18. A particle has a mass of 1.67x10-27 kg and a charge of -1.6x10-19 C. What type of particle is it?
5
Nuclear Reactions
In all nuclear reactions, _____________________and _____________________
must be conserved.
15. During the process of a Beta emission, a neutron in the nucleus of an atom is converted into a
proton, an electron, an electron antineutrino, and energy.
Neutron
proton + electron + electron antineutrino + energy
Based on conservation laws, how does the mass of the neutron compare to the mass of the proton?
Since charge must be conserved in the reaction shown, what charge must an electron antineutrino carry?
Binding Energy and Mass Defect
When protons and neutrons come together to form a nucleus, it is observed that the actual mass of the
nucleus is _________________ than the mass of the individual particles that make up the nucleus
This "missing mass" is known as the _______________________
A small quantity of the mass of the particles is converted into ____________________ to keep the
nucleus together
Anti-matter
Antimatter is just like ordinary matter, but with opposite charge
You could build an entire universe out of antimatter!
An anti-electron (positive) orbiting an anti-proton (negative) would make an anti-hydrogen.
2 anti-hydrogens and an anti-oxygen could make anti-H2O.
Everything in this universe would behave exactly like ours - opposite charges would attract and like
charges would repel.
But this universe couldn't coexist with ours - if antimatter comes in contact with ordinary matter, they
annihilate each other and become PURE ENERGY (via E=mc2)!
Fuel
Gasoline (chemical energy)
How much energy is there in antimatter?
Joules from 1 kg fuel
Mass (kg) converted to energy
5 x 10-10 kg
Uranium (nuclear energy)
Hydrogen (nuclear energy)
Matter/antimatter annihilation
%
0.0009 kg
6.4 x 1014 J
1 kg
100%
6
The Standard Model
The standard model is the current model for all matter/particles and how they interact.
The Fundamental Forces of Nature
______________ Force
______________ Force
______________ Force
______________ Force
Classification of Matter / Particles of the Standard Model
Matter
Leptons
Hadrons
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Quarks
Baryons
Mesons
Antiquarks
Proton
Neutron
Electron
19. Name the fundamental interaction that best fits the following descriptions:
The weakest interaction________________________
The strongest interaction_______________________
Responsible for nuclear decay____________________
Acts between nucleons________________________
Only acts over very short distances_________________
Is responsible for like charges repelling_________________
Is related to the binding energy of a nucleus__________________
20. Can a particle consisting of 3 up quarks exist? If so, what charge would it have?
21. What is the charge of the meson containing an up quark and an anti-down quark?
22. A subatomic particle is made of 2 strange quarks and 1 bottom quark.
a) What is the charge of this particle?
b) What is the classification name of this subatomic particle?
23. What is the charge of a baryon consisting of 2 anti-strange quarks and 1 anti-charm quark?
24. What is the charge of a meson consisting of a top quark and an anti-charm quark.
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Problems
25. The strong force is the force of
1. repulsion between protons
2. attraction between protons and electrons
3. repulsion between nucleons
4. attraction between nucleons
26. The tau neutrino, the muon neutrino, and the
electron neutrino are all
1. leptons
2. hadrons
3. baryons
4. mesons
Base your answers to questions 27 and 28 on the
information below.
A lambda particle consists of an up, a down, and a
strange quark.
27. A lambda particle can be classified as a
1. baryon
2. lepton
3. meson
4. photon
28. What is the charge of a lambda particle in
elementary charges?
29. According to the Standard Model, a proton is
constructed of two up quarks and one down quark
(uud)
and a neutron is constructed of one up quark and
two down quarks (udd). During beta decay, a
neutron
decays into a proton, an electron, and an electron
antineutrino. During this process there is a
conversion of a
1. u quark to a d quark
2. d quark to a meson
3. baryon to another baryon
4. lepton to another lepton
30. Which statement is true of the strong nuclear
force?
1. It acts over very great distances
2. It holds protons and neutrons together
3. It is much weaker than gravitational forces
4. It repels neutral charges
31. Which combination of quarks could produce a
neutral baryon?
1. cdt
2. cts
3. cdb
4. cdu
32. A meson may not have a charge of
1. +1e
2. +2e
3. 0e
4. -1e
33. The charge of an antistrange quark is
approximately
1. +5.33 × 10-20 C
2. -5.33 × 10-20 C
3. +5.33 × 1020 C
4. -5.33 × 1020 C
34. Compared to the mass and charge of a proton, an
antiproton has
1. the same mass and the same charge
2. greater mass and the same charge
3. the same mass and the opposite charge
4. greater mass and the opposite charge
35. According to the Standard Model of Particle
Physics,
a meson is composed of
1. a quark and a muon neutrino
2. a quark and an antiquark
3. three quarks
4. a lepton and an antilepton
36. A particle unaffected by an electric field could
have a
quark composition of
1. css
2. bbb
3. udc
4. uud
37. A lithium atom consists of 3 protons, 4
neutrons, and 3 electrons. This atom contains a total
of
1. 9 quarks and 7 leptons
2. 12 quarks and 6 leptons
3. 14 quarks and 3 leptons
4. 21 quarks and 3 leptons
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Review Checklist
Demonstrate understanding of energy quantization
1. Explain why an atom of a given element can produce only specific photons of light when heated.
Demonstrate understanding of wave/particle duality of and matter
2. Light exhibits properties of (a) waves only (b) particles only (c) both waves and particles
3. Which phenomenon best supports the theory that light has a particle nature?
a. electron momentum b. electron diffraction
c. photon momentum
d. photon diffraction
4. Which of the following could be used to demonstrate the wave properties of matter?
a. asteroid
b. electron
c. bicycle
d. proton
e. apple
Demonstrate understating of photon properties. Use equation to determine photon energy, frequency,
and/or wavelength. Use EM Spectrum Chart to determine photon type.
5. What is the energy of a photon with a frequency of 2.5 x 1013 hertz?
6. What is the wavelength of a photon with an energy of 3.0 x 10-18 joules?
7. What type of photon has an energy of 9.0 x 10-19 joules?
Demonstrate understanding of mass/energy duality. Use equation to determine relationship between
energy and mass. Be able to convert between universal mass units and mega-electron-volts.
8. How much energy is contained in 3.0 kilograms of matter?
9. How much mass is needed to produce 2.0 mega-joules of energy?
10. How much energy is contained in 5.0 universal mass units of matter?
Determine ionization energies and kinetic energies for liberated electrons
11. What energy is needed to liberate an electron from the c-level of a mercury atom?
12. A hydrogen atom with an electron in the n = 3 level is hit by a photon with an energy of 2.51
electron-volts. What kinetic energy will the electron have as it leaves the atom?
Use equation to determine the outcome of a photon absorption, emission, or an energy level transition.
Convert from joules to electron-volts; determine photon energy and/or frequency and type using the EM
Spectrum Chart.
13. A photon causes an electron to jump from the b-level to the e-level of a mercury atom. What energy
did this photon need to have? What was its frequency? What type of photon was it?
14. A 10.2 eV photon is emitted by an electron in a hydrogen atom as it returns to the ground state.
What energy level did the electron drop from?
15. What photon energy is needed to cause an electron to leave the h-level of a mercury atom with a
kinetic energy of 4.0 electron volts?
16. An electron in the d-level of a mercury atom drops to the ground state. How many different photons
could be produced during this transition?
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17. Explain why a 3.0 electron-volt photon will have no effect on an electron in the n=2 level of a
hydrogen atom.
Understand the importance and meaning of the emission and absorption spectrum. Identify the
components of a sample by its spectrum.
18. Use the spectrums below to determine which of the four samples contain “Element X”.
Classify and determine the charge of various particles. Explain how matter and anti-matter are related.
Describe the fundamental forces of the Standard Model.
19. Classify each of the following as either a: lepton, anti-lepton, baryon, antibaryon, meson or ‘not
enough information’.
(1) A particle made of 3 quarks. (2) A particle with no charge. (3) An electron. (4) A neutron. (5) A
particle composed of an up quark and an anti—down quark. (6) A particle composed of three anti-up
quarks. (7) A muon-neutrino. (8) A particle with a charge of +2. (9) An anti-electron.
20. What is the charge on a particle containing two down quarks and one up quark?
21. What is the charge on a particle containing a down quark and an anti-up quark?
22. A hydrogen atom consists of a proton and an electron. An anti-hydrogen atom consists of an antiproton and an anti-electron (positron). Explain the differences and similarities between hydrogen and
anti-hydrogen in terms of mass, charge, and emission spectrum.
23. Which of the particles would not be effected by the electromagnetic force? (1) electron (2) antimuon (3) tau-neutrino (4) ucb (5) udd
24. Which of the particles would not be effected by the strong force? (1) proton (2) meson (3) electronneutrino (4) muon
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Answers:
1. Energy levels are quantized
2. C
3. C
4. B,d
5. 1.66 x 10-20 J
6. 4.52 x 1015 Hz
7. Ultraviolet
8. 2.7 x 1017 J
9. 2.2 x 10-11 kg
10. 4655 MeV
11. 5.52 eV
12. 1 eV
13. -2.03 eV / 3.2 x 10-19 J / 4.8 x 1014 Hz / visible
14. N=2
15. -5.57 eV
16. 6 (d->c, c->b,b->a,d->b,c->a,d->a)
17. Would take you to -0.4 eV, which is not an energy level
18. A,D
19. B,X,L,B,M,anti-B,L,B,anti-L
20. 0e
21. -1e
22. Same in all ways (overall charge is same, but individual charge is different)
23. 3,5
24. 3,4
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