Chapter 9: Atomic and Nuclear Phenomina Flashcards
Briefly describe the photoelectric effect and photosynthesis.
As a photo of light enters the chloroplast in a plant cell, it reacts with chlorophyll, causing the ejection of an electron from certain magnesium containing dyes. This electron feeds in synthetic pathways that ultimately result in glucose production. This is a primary example of the photoelectric effect.
What is the photoelectric effect?
When light of a sufficiently high frequency (typically blue to ultraviolet light) is incident on a metal in a vacuum, the metal atoms emit electrons. This is called the photoelectric effect.
Electrons liberated from the metal by the photoelectric effect will produce a net charge per unit time, or CURRENT. Provided that the light beams frequency is above the threshold frequency of the metal, light beams of greater intensity produce larger current in this way.
How is intensity of light related to the photoelectric effect?
Provided that the light beam frequency is above the threshold frequency of the metal, light beams of greater intensity produce larger currents.
The higher the intensity of the light beam, the greater the number of photons per unit time that fall on an electrode, producing a greater number of electrons per unit time liberated from the metal.
When the lights frequency is above the threshold frequency, the magnitude of the resulting current is directly proportional to the intensity (and amplitude) of the light beam.
What is the proportionality between magnitude of resulting current and intensity (and amplitude) of a light beam?
When the light frequency is above the threshold frequency, the magnitude of the resulting current is directly proportional to the intensity, and amplitude, of the light beam.
What is the proportionality between light intensity and amplitude?
What is threshold frequency (fT)? What does threshold frequency depend on?
The minimum frequency of light that causes ejection of electrons is known as the threshold frequency fT. Threshold frequency depends on the type of metal being exposed to the radiation.
Why is the photoelectric effect, for all intense and purposes, an all or nothing response?
If the frequency of the incident photon is less than the threshold frequency, then no electron will be ejected because the photons do not have the sufficient energy to dislodge the electron from its atom.
If the frequency of the incident photon is greater than the threshold frequency, then an electron will be ejected, and the maximum kinetic energy of the ejected electron will be equal to the difference between hf and hfT (the work function).
What is the work function?
W=hfT
In solid-state physics, the work function is the minimum thermodynamic work needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface (hfT).
The work function can be thought of as activation energy. It must be matched or exceeded to cause the reaction (escape of an electron) to occur.
What will happen if the frequency of incident light is less than the threshold frequency?
What will happen if the frequency of incident light is more than the threshold frequency?
What will happen if the incident light beams frequency is above the threshold frequency and is of a high intensity?
An electron will be ejected.
An electron will not be ejected.
More current will be produced, the net charge flow per unit time.
How do you calculate the maximum kinetic energy of an ejected electron?
If the frequency of the incident photon is greater than the threshold frequency, then an electron will be ejected, and the maximum kinetic energy of the ejected electron will be equal to the difference between hf and hfT (the energy of the electron and the work function).
How do we calculate the energy of a photon?
How do we calculate wavelength with the given frequency of light given the energy of a photon?
In terms of energy and wavelength, what does it mean for waves with higher frequency? For waves with lower frequency?
Higher frequency waves have shorter wavelength and higher energy.
Lower frequency waves have longer wavelength and lower energy.
How do we calculate the maximum kinetic energy of an ejected electron? What are the conditions by which an electron will be ejected?
The conditions by which an electron will be ejected are that the electron has more energy than the work function (the energy required to eject and electron, hfT)
Example photoelectric effect page 332
MCAT concept check photoelectric effect 9.1 page 332 question 1
How does the work function relate to the energy necessary to emit an electron from a metal?
The energy of the photon must be greater than the work function in order for an electron to be emitted from the metal.
From the book: the work function describes the minimum amount of energy necessary to emit an electron. Any additional energy from a photo will be converted to excess kinetic energy during the photoelectric effect.
In the photoelectric effect, does higher intensity light eject more electrons or higher kinetic energy electrons?
In the photoelectric effect, a higher intensity of light results in more electrons being ejected, not higher kinetic energy of the individual electrons; the kinetic energy of the electrons is determined by the frequency of the light, not its intensity.
More light intensity increases the amount of electrons emitted, observed as increased current.
MCAT concept check photoelectric effect 9.1 page 332 question 2
What does the threshold frequency depend upon?
The threshold frequency depends on the type of metal being exposed to the radiation.
The threshold frequency depends on the chemical composition of a material, that is the identity of the metal.
MCAT concept check photoelectric effect 9.1 page 332 question 3
What electrical phenomenon results from the application of the photoelectric effect?
The accumulation of moving electrons creates a current during the photoelectric effect.
As long as the frequency of light is greater than the threshold frequency ( which also means the energy of the photon is greater than the work function) electrons will be emitted and a current is created.
Higher energy electrons manifest a higher kinetic energy, higher intensity light emits more electrons and increases the current observed.
What does the Bohr model state?
The Bohr model states that electron energy levels are stable and discrete, corresponding to specific orbits.
An electron can jump from a lower energy to a higher energy orbit by absorbing a photon of light of precisely the right frequency to match the energy difference between the orbits (E=hf).
If a photon does not carry enough energy, then the electron cannot jump to a higher energy level.
When an electron falls from a higher energy level to a lower energy level, a photon of light is emitted with an energy equal to the energy difference between the two orbits.
MCAT concept check absorption and emission of light 9.2 page 336 question 1
What determines the absorption spectrum of a single atom?
The energy differences between ground state electrons and higher level electron orbits determine the frequencies of light a particular material absorbs (its absorption spectrum).
MCAT concept check absorption and emission of light 9.2 page 336 question 2
True or false: small changes in chemical structure only minimally impact light absorption and emission patterns.
False. Small changes, such as protonation and deprotonation, change in oxidation state or bond order, and other differences may cause dramatic changes in light absorption in a material.
MCAT concept check absorption and emission of light 9.2 page 336 question 3
During which electronic transitions is photon emission most common?
When electrons transition from a higher energy state to a lower energy state, they will experience photon emission.
MCAT concept check absorption and emission of light 9.2 page 336 question 4
What causes fluorescence?
Fluorescence is a special step wise photon emission in which an electron returns to the ground state through one or more intermediate excited states.
Each energy transition releases a photon of light. With smaller energy transitions than the initial energy absorbed, these materials can release photons of light in the visible range.
What is the mass defect?
The mass defect is the difference in mass between what we would expect by taking the sum of all the masses of the protons and neutrons, and the actual mass of the nucleus.
The mass defect is the mass that contributed to the binding energy of the nucleus.
What is the equation for the equivalence of matter and energy?
What is the strong nuclear force?
The strong nuclear force is what attracts nucleons (protons and neutrons) together.
The strong nuclear force only acts over extremely small distances (less than a few times the diameter of a nucleon. This means that nucleons need to get very close together in order for the strong nuclear force to hold them together.
What is nuclear binding energy?
Nucleons have to get very close to each other in order for the strong nuclear force to hold them together.
The bonded system is at a lower energy level than the unbounded constituents, and the difference in energy must be radiated away in the form of heat or light or other em radiation before the mass defect becomes apparent. This energy is called the binding energy.
The amount of mass that is transformed into the dissipated energy will be a measurable fraction of the initial total mass.
What element has the highest binding energy? What does this suggest about the stability of that element?
Iron has the highest binding energy per nucleon. This implies that iron contains the most stable nucleus.
In general, intermediate sized nuclei are more stable than very large or very small nuclei.
In terms of size of nuclei, what is the general trend for stability of a nucleus?
The general trend is that intermediate sized nuclei are more stable than very large or very small nuclei.
What are the four fundamental forces of nature?
Strong nuclear force, weak nuclear force, electrostatic forces, and gravitation.
Mass defect example page 337
MCAT concept check nuclear binding energy and mass defect page 338 question 1
Defined the following: strong nuclear force, mass defect, binding energy.
The strong nuclear force is one of the four primary forces and provide provides the adhesive force between the nucleons (protons and neutrons) in the nucleus.
Mass defect is the apparent loss of mass when nucleons come together, as some of the mass is converted into energy.
That energy is called the binding energy.
MCAT concept check nuclear binding energy and mass defect page 338 question 3
How does the mass defect relate to the binding energy?
Mass defect is related to the binding energy, such that there is a transformation of nuclear matter to energy with the result and loss of matter. They are related by the equation E=mcsquared.
What is isotopic notation?
What is fusion?
Fusion occurs when small nuclei combine to form larger nucleus.
For example. Stars power themselves by fusing four H nuclei to form one He nucleus. This energy that is produced accounts for the mass defect that arises from the formation of He nuclei from H nuclei.
Fusion energy is directly related to mass defect; the energy released in a fusion reaction comes from the difference in mass between the initial nuclei and the resulting heavier nucleus, which is known as the “mass defect”.
What is fission?
Fission is the process by which a large nucleus splits into smaller nuclei. Through absorption of a low energy neutron, fission can be induced in certain nuclei.
Fission reaction example page 341
What is radioactive decay? What three types of radioactive decay problems might we see?
Radioactive decay is a naturally occurring spontaneous decay of certain nuclei accompanied by the emission of specific particles.
- Integer arithmetic of particle and isotope species.
- Radioactive half life problems.
- The use of exponential decay curves and decay constants.
How do we balance nuclear reactions?
When balancing nuclear reactions, the sum of the atomic numbers and mas numbers must be the same on both sides of the equation.
Start by balancing the number of protons (atomic numbers). Often times, wrong answer choices will simply have an error in the number of protons and can be eliminated before checking mass numbers.
What is the mass defect?
The mass defect is the difference in mass between what we would expect by taking the sum of all the masses of the protons and neutrons, and the actual mass of the nucleus.
The mass defect is the result of binding energy
What is alpha decay?
Need to draw this and put an image in the answer.
Alpha decay is the emission of an alpha particle.
An alpha particle is an He nucleus that contains no electrons. An He nucleus has 2 protons and 2 neutrons (a total of 4 nucleons).
The notation for an alpha particle is in the image.
What is an alpha particle? What is the notation for an alpha particle? What is the charge of an alpha particle?
An alpha particle is a He nucleus with no electrons (2 protons, 2 neutrons, zero electrons).
The charge of an alpha particle is +2e, positive two elementary charges.
Express alpha decay as a balanced equation using ISOTOPIC NOTATION
Be intricately familiar with this notation.
Alpha decay example page 342
Bonus. Identify the parent and daughter isotope (will need periodic table)
The image is incorrect. Fix it draw it.
What is beta decay? What is a beta particle? What are beta particles emitted from?
Beta decay is the emission of a beta particle.
A beta particle is an electron and is given by the symbol in the image. Beta particles are emitted from the nucleus when a neutron decays into a proton, creating a beta particle and an antineutrino.
What is positron emission?
In some cases of induced decay (positron emission), a positron is released, which has the mass of an electron but carries a positive charge.
What is a positron?
A positron has the mass of an electron and carries a positive charge.
During beta- decay, a neutron is converted into a proton and a beta- particle. Express this in isotopic notation.
During beta+ decay, a proton is converted into a neutron and a beta+ is emitted. Express this in isotopic notation.
Does beta decay produce a different element? How so?
Both beta- and beta+ decay produce different elements. This is because the decay changes the number of protons, the defining feature of an element.
Beta- decay, neutron is converted to a proton, emitting an electron. This adds a proton (higher atomic number) while maintaining mass number.
Beta+ decay, proton is converted to a neutron, emitting a positron. This reduces the atomic number while maintaining the mass number.
Beta decay example page 343
Observe the isotopic notation for the beta particle.
Negative beta decay produces what particle? Positive beta decay produces what particle?
Negative beta decay produces a negative beta particle, positive beta decay produces a positive beta particle.
What is gamma decay? What are gamma rays?
Gamma decay is the emission of gamma rays. Gamma rays are high energy (high frequency) photons. They carry no charge and simply lower the energy of the parent nucleus without changing the mass number or the atomic number. High energy state of the parent nucleus may be represented by an asterisk in the balanced isotopic notation equation.
How is gamma decay expressed as a balanced equation using isotopic notation?
Does gamma decay change the atomic number or mass number?
Nope.
Gamma decay, positron emission, alpha decay example page 344
Refer to book if needed to wrap this up. This is an excellent way to solidify our understanding here.
What is electron capture? What happens to the mass number? Why?
Certain unstable radionuclides are capable of capturing an inner electron that combines with a proton to form a neutron, releasing a neutrino.
The atomic number is mow Z-1, but the mass number remains the same as a proton is transformed to a neutron.
Electron capture can be thought of as the reverse of beta- decay.
How do we express electron capture using isotopic notation?
What is half life?
In radioactive particles, the half-life (T1/2) of the sample is the time it takes for half of the sample to decay.
In each subsequent half life, one half of the remaining sample decays so that the remaining amount asymptotically approaches zero.
Half life example page 345
What is the decay constant?
The decay constant is the probability that a radioactive atom will decay in a given amount of time.
What is the exponential decay equation?
The exponential decay equation tells us how the number of radioactive nuclei changes with time.
How is half life related to the decay constant?
Describe the graph of a typical exponential decay curve.
When is “all” of a radioactive sample
Considered decayed?
Around 7-8 half lives.
MCAT concept check Nuclear Reactions page 347 question 1
True or false. Nuclear fission and nuclear fusion both release energy.
True. Both nuclear fusion and nuclear fusion reactions release energy. They may seem like inverses of each other, but they both release energy.
MCAT concept check Nuclear Reactions page 347 question 2
MCAT concept check Nuclear Reactions page 347 question 3
MCAT concept check Nuclear Reactions page 347 question 4
How many half lives are necessary for the complete decay of a radioactive sample?
The portion remaining will never quite reach zero. However, for the theoretical consideration, all of a sample is considered to have decayed after 7 to 8 half lives.
MCAT concept check Nuclear Reactions page 347 question 5
Which type of nuclear decay could be detected in an atomic absorption spectrum?
Because gamma radiation produces electromagnetic radiation, rather than nuclear fragments, it can be detected on an atomic absorption spectrum.
MCAT mastery atomic and nuclear phenomena page 326 question 1
First we solve for the energy of the photon (hf).
Then we solve for maximum kinetic energy (hf-hfT).
Once we have kinetic energy, we can solve for velocity (K=1/2mv^2…..
v=(2k/m)^1/2)
MCAT mastery atomic and nuclear phenomena page 326 question 2
First we solve for the energy of the photon, Kmax=hf-hfT.
Second we solve for the frequency, E=hf.
Then we solve for wavelength c=f(lambda)…. Wavelength=c/f.
Careful with units and exponents. Area of misunderstanding on first try is highlighted in yellow.
MCAT mastery atomic and nuclear phenomena page 326 question 3
MCAT mastery atomic and nuclear phenomena page 326 question 4
First we need to convert electron volts to joules (conversion given in the question)
Second, we need to solve for wavelength (wavelength=hc/E)
The area outlined in yellow on the answer image demonstrates the need to make approximations to solve these problems. Use as much scratch paper as you need, you don’t have to do it all in your head.
MCAT mastery atomic and nuclear phenomena page 326 question 5
MCAT mastery atomic and nuclear phenomena page 326 question 6
MCAT mastery atomic and nuclear phenomena page 326 question 7
MCAT mastery atomic and nuclear phenomena page 327 question 8
First understand that the mass defect equals the mass expected minus the mass observed.
Refer to a periodic table to get the atomic number of argon.
Calculate the expected mass and then subtract the mass observed (mass observed is given in problem)
This will give us the mass defect (m in amu) to plug into E equals MC squared.
MCAT mastery atomic and nuclear phenomena page 326 question 9
MCAT mastery atomic and nuclear phenomena page 326 question 10
We need to know the mass defect between the reactants and the products. Do this by adding the mass of the reactants and subtracting the mass of the products.
This will give you an atomic mass unit to use to convert to MeV using the conversion given in the question.
MCAT mastery atomic and nuclear phenomena page 326 question 11
The book just reasons this one out, and as did we when we first encountered this question.
There’s an interesting example using mathematical way to reason through this problem in the image in black.
MCAT mastery atomic and nuclear phenomena page 326 question 12
We recognized that lambda is the decay constant which is the change of n (number of nuclei not yet decayed) over change in time. The answer is negative lambda.
MCAT mastery atomic and nuclear phenomena page 326 question 13
MCAT mastery atomic and nuclear phenomena page 326 question 14
We reasoned through this well and came up with the correct answer.
MCAT mastery atomic and nuclear phenomena page 326 question 15
In Alpha decay, an element loses two protons. In positron decay, a proton is converted into a neutron. Gamma decay has no impact on the atomic number of the nuclide. Therefore, two alpha decays and two positron decays will yield a daughter nuclide with six fewer protons than the parent nuclide.
Relevant equations and relationships for chapter 9: nuclear and atomic phenomena
