Unit 21: Nuclear Chemistry
Why some nuclei hold together forever and others fly apart on a schedule you can set a clock by, and what happens when one nucleus splits or two combine.
11 topics · 37 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
21.1 Nuclear Stability and the Band of Stability
- How it worksHow does plotting every stable nucleus's proton count against its neutron count reveal a narrow band of stability that heavier elements must hug more closely?
- Common mistakeWhy isn't a 1-to-1 ratio of protons to neutrons enough to keep a heavy nucleus stable the way it works for light elements?
- Going furtherWhat happens to the neutron-to-proton ratio needed for stability as you look at heavier and heavier elements on the band of stability?
Your turn1 of 2
Light elements like carbon are stable with roughly equal numbers of protons and neutrons. Why isn't that same 1-to-1 ratio enough to keep a heavy nucleus, like one with 80 or more protons, stable?21.1 Binding Energy and Mass Defect
- How it worksHow does Einstein's E equals mc squared convert a nucleus's tiny missing mass into the enormous energy holding it together?
- Worked exampleFind the binding energy per nucleon for a helium-4 nucleus given a mass defect of 0.0304 amu.
- Common mistakeWhy isn't the 'missing mass' in a nucleus actually missing at all, just converted into binding energy?
- Ties togetherHow does binding energy per nucleon peaking around iron connect back to why both fission of heavy nuclei and fusion of light nuclei release energy?
Your turn1 of 2
Find the binding energy per nucleon, in MeV, for a nucleus with a mass defect of 0.351 amu and 157 total nucleons (1 amu = 931.5 MeV).21.2 Nuclear Equations and Conservation Rules
- How it worksHow do conservation of mass number and conservation of atomic number let you identify an unknown particle in a nuclear equation?
- Worked exampleFind the missing product when uranium-238 undergoes alpha decay.
- Common mistakeWhy can't a nuclear equation be balanced the same way an ordinary chemical equation is, by matching up elements on each side?
Your turn1 of 2
A nucleus with mass number 235 undergoes alpha decay, emitting a helium-4 nucleus (mass number 4). Find the mass number of the resulting daughter nucleus.21.3 Types of Radioactive Decay: Alpha, Beta, and Gamma
- How it worksHow do alpha, beta, and gamma decay each change a nucleus's mass number and atomic number in a different way?
- How it worksWalk me through how beta decay converts a neutron into a proton, ejecting an electron in the process.
- Worked exampleFind the daughter nucleus produced when carbon-14 undergoes beta decay.
- Common mistakeWhy isn't a beta particle the same thing as an electron orbiting the nucleus that gets knocked loose?
Your turn1 of 2
A nucleus with atomic number 66 undergoes beta decay (a neutron converts to a proton, ejecting an electron). Find the atomic number of the resulting daughter nucleus.21.3 Radioactive Decay Kinetics and Half-Life
- How it worksHow does radioactive decay following first order kinetics mean each nucleus has a fixed probability of decaying, independent of the sample's age?
- Worked exampleFind how much of a 10.0 g sample of a radioisotope with a half-life of 5.0 days remains after 20 days.
- Common mistakeWhy doesn't a sample's radioactivity ever reach exactly zero, no matter how many half-lives pass?
Your turn1 of 2
Find how much of a 36 g sample of a radioisotope with a half-life of 7 days remains after 57 days.21.3 Radiocarbon Dating
- How it worksHow does a living organism maintaining a constant carbon-14 ratio while alive, then losing carbon-14 at a fixed rate after death, make dating possible?
- Worked exampleFind the age of a sample that has 25 percent of its original carbon-14 remaining, given carbon-14's half-life of 5,730 years.
- Common mistakeWhy doesn't radiocarbon dating work for a fossil that's a billion years old?
Your turn1 of 2
Find the age of a sample that has 64 percent of its original carbon-14 remaining, given carbon-14's half-life of 5,730 years. Use age = negative the half-life times the natural log of the fraction remaining, divided by the natural log of 2.21.4 Nuclear Transmutation
- How it worksHow does bombarding a stable nucleus with a particle like an alpha particle or a neutron force it to become an entirely different element?
- Worked exampleFind the product formed when nitrogen-14 is bombarded with an alpha particle, releasing a proton.
- Common mistakeWhy isn't nuclear transmutation the same process as the radioactive decay a nucleus undergoes entirely on its own?
Your turn1 of 2
A nucleus with atomic number 66 is bombarded with a particle of atomic number 1, and the collision releases a particle of atomic number 2. Find the atomic number of the resulting product nucleus (protons are conserved: the target's protons plus the bombarding particle's protons equal the released particle's protons plus the product's protons).21.4 Nuclear Fission and Chain Reactions
- How it worksHow does each fission event release multiple neutrons that go on to split additional nuclei, building a self-sustaining chain reaction?
- How it worksWalk me through the difference between a controlled chain reaction inside a nuclear reactor and an uncontrolled one in a weapon.
- Common mistakeWhy isn't every neutron released by fission guaranteed to trigger another fission event?
- Going furtherWhat happens to a chain reaction once its neutrons are absorbed by control rods faster than new fissions can produce them?
Your turn1 of 2
A fission event releases 3 neutrons on average, and a fraction 0.689 of them go on to cause another fission. Find the multiplication factor k (the average number of new fissions caused by each fission).21.4 Nuclear Fusion and Stellar Nucleosynthesis
- How it worksHow does forcing two positively charged nuclei close enough to fuse require overcoming their mutual electrostatic repulsion with extreme temperature and pressure?
- Common mistakeWhy hasn't controlled nuclear fusion been harnessed on Earth as easily as nuclear fission has, despite fusion releasing more energy per unit mass?
- Going furtherWhat happens to the elements a star can fuse in its core as it runs out of hydrogen and progresses toward heavier fuels?
Your turn1 of 2
A fusion reaction converts mass into energy with a mass defect of 0.0212 amu. Find the energy released, in MeV (1 amu = 931.5 MeV).21.5 Uses of Radioisotopes in Medicine
- How it worksHow does choosing a radioisotope with an appropriately short half-life and a specific decay type make it useful for imaging without excess radiation exposure?
- Worked exampleFind why technetium-99m, with a half-life of about 6 hours, is a practical choice for a same-day medical imaging procedure.
- Common mistakeWhy isn't every radioisotope automatically an equally good choice for a medical application?
Your turn1 of 2
A patient is injected with 22 millicuries of technetium-99m (half-life about 6 hours) for an imaging procedure. Find how much activity remains after 16 hours.21.6 Biological Effects of Radiation
- How it worksHow does ionizing radiation damage biological tissue by knocking electrons loose from the molecules that make up living cells?
- How it worksWalk me through why alpha particles, though easily stopped by skin, become especially dangerous once a source is inhaled or swallowed.
- Common mistakeWhy isn't the danger of a radiation source determined only by how strongly it's emitting, ignoring the type of radiation and its exposure route?
- Going furtherWhat happens to a material's ability to shield against radiation as you move from stopping alpha particles to stopping gamma rays?
Your turn1 of 2
Alpha particles are easily stopped by a sheet of paper or the outer layer of skin, yet they become especially dangerous once an alpha-emitting source is inhaled or swallowed. Why?