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chem ch 21
| Question | Answer |
|---|---|
| How do chemical and nuclear reactions differ? | Chemical reactions involve valence electrons; nuclear reactions involve changes in the nucleus. |
| Radiation | Spontaneous emission of particles and energy from an unstable nucleus. |
| Radioactive decay | The spontaneous emission of radiation from an unstable nucleus. |
| Radionuclide / radioisotope | An atom with a radioactive nucleus; a radioactive form of a specific isotope. |
| Four fundamental forces listed in the notes | Strong nuclear force, electromagnetic force, weak nuclear force, and gravitational force. |
| Role of the strong nuclear force in a nucleus | It provides an attractive binding force between nucleons that helps hold the nucleus together. |
| Why do neutrons increase nuclear stability? | They add strong nuclear attraction without adding positive charge, helping offset proton-proton electrical repulsion. |
| Why are very large nuclei often unstable? | The strong nuclear force weakens with greater distance, while electromagnetic repulsion between protons remains significant. |
| Alpha particle symbol and composition | ⁴₂He; two protons and two neutrons. |
| Alpha-particle charge, shielding, and penetration | +2 charge; stopped by paper or skin; least penetrating of the listed particles. |
| Beta-minus particle symbol and nuclear change | ⁰₋₁e; a neutron changes into a proton. |
| Beta-minus shielding and penetration | Stopped by thick clothing; about 100 times more penetrating than alpha radiation. |
| Gamma radiation | High-energy photons emitted as a nucleus loses excess energy while moving toward stability. |
| Gamma shielding and penetration | Shielded by lead or concrete; about 10,000 times more penetrating than alpha radiation. |
| Positron symbol and nuclear change | ⁰₊₁e; a proton changes into a neutron. |
| What happens when a positron meets an electron? | They annihilate each other and release energy. |
| Electron capture | A nucleus captures an inner electron; a proton changes into a neutron. |
| How do mass number and atomic number change in alpha decay? | Mass number decreases by 4; atomic number decreases by 2. |
| How do mass number and atomic number change in beta-minus decay? | Mass number stays the same; atomic number increases by 1. |
| How do mass number and atomic number change in positron emission or electron capture? | Mass number stays the same; atomic number decreases by 1. |
| Why does gamma emission not change an element’s identity? | Gamma emission releases energy only; it changes neither protons nor neutrons. |
| Balance this alpha decay: ²²⁶₈₈Ra -> ⁴₂He + ? | ²²²₈₆Rn. |
| Balance this beta-minus decay: ¹³¹₅₃I -> ⁰₋₁e + ? | ¹³¹₅₄Xe. |
| Balance this positron emission: ¹¹₆C -> ⁰₊₁e + ? | ¹¹₅B. |
| Balance this electron capture: ⁸¹₃₇Rb + ⁰₋₁e -> ? | ⁸¹₃₆Kr. |
| Stable proton-to-neutron pattern for elements 1–20 | Approximately 1 proton to 1 neutron. |
| Stable neutron requirement for elements 21–83 | More neutrons than protons are needed for stability. |
| Nuclei with atomic number greater than 83 | Generally unstable and radioactive. |
| Which decay process helps a nucleus with excess neutrons? | Beta-minus emission, which converts a neutron into a proton. |
| Magic numbers of protons or neutrons | 2, 8, 20, 28, 50, 82, and 126. |
| Why are even numbers of protons and neutrons often more stable? | Even nucleon counts are more stable, similar to filled electron shells. |
| Transmutation | Changing one element into another through a nuclear reaction. |
| Nuclear bombardment | Producing a nuclear reaction by striking a nucleus with a particle. |
| Why are neutrons useful projectiles in nuclear bombardment? | They have no charge, so they do not need to overcome electrical repulsion from the nucleus. |
| Transuranium elements | Artificial, usually unstable elements with atomic number greater than 92. |
| Balanced equation for alpha bombardment of nitrogen-14 producing oxygen-17 | ¹⁴₇N + ⁴₂He -> ¹⁷₈O + ¹₁p. |
| Shorthand for nitrogen-14 bombarded by alpha to produce oxygen-17 and a proton | ¹⁴N(α,p)¹⁷O. |
| Half-life | The time required for a radioisotope to decay to half its original amount. |
| Relationship between half-life and the decay constant k | They are inversely related: k = 0.693 / t₁/₂. |
| Formula for remaining amount after a non-integer number of half-lives | Nt = N0(1/2)^n, where n = t / t₁/₂. |
| Formula for finding elapsed time from initial and remaining amounts | ln(Nt/N0) = -kt. |
| A radioisotope has a half-life of 5.30 days. What fraction remains after 20.5 days? | (1/2)^(20.5/5.30) = (1/2)^3.87, or about 1/14.6. |
| A 1.00 g sample has a half-life of 5.30 days. How much remains after 20.5 days? | Approximately 0.0685 g. |
| Carbon-14 has a half-life of 5715 years. A 24.0 g sample has 11.5 g remaining. Approximately how old is it? | About 6033 years. |
| Why is radioactive decay useful for dating objects? | The predictable half-life relationship connects the fraction remaining to elapsed time. |
| Mass defect | The difference between the combined masses of separate protons and neutrons and the actual mass of the nucleus. |
| Why is a nucleus less massive than its separate nucleons? | Some mass was converted into binding energy when the nucleus formed. |
| Equation connecting mass defect and nuclear binding energy | E = mc². |
| Nuclear binding energy | The energy required to separate a nucleus completely into its individual protons and neutrons. |
| Why are spontaneous nuclear reactions exothermic? | Lost mass is converted into released energy. |
| Steps to calculate mass defect | Add the separate proton and neutron masses, then subtract the measured nuclear mass. |
| Mass defect of a helium nucleus with nucleon mass total 4.03188 amu and nuclear mass 4.00150 amu | 0.03038 amu. |
| Before using E = mc², what must be done to the mass defect? | Convert the mass defect from amu to kilograms. |
| Value of the speed of light used in E = mc² | 3.00 × 10⁸ m/s. |
| How is binding energy per nucleon found? | Divide total nuclear binding energy by the total number of nucleons. |
| Why is iron-56 especially stable? | It has the highest nuclear binding energy per nucleon on the graph. |
| Mass defect for polonium-210 with separate nucleon mass 211.7094 amu and nuclear mass 209.9828 amu | 1.7266 amu. |
| Fission | Splitting a large nucleus into two smaller nuclei of approximately equal mass. |
| Fusion | Combining two small nuclei to form a larger nucleus with slightly lower mass. |
| Which releases more energy according to the materials: fission or fusion? | Fusion. |
| Why can fission release energy? | Heavy nuclei split into more stable medium-sized nuclei, and the excess mass becomes energy. |
| Why can fusion release energy? | Very light nuclei combine into a more stable larger nucleus, releasing energy. |
| Basic fission reaction described for uranium-235 | ²³⁵U absorbs a neutron, becomes unstable uranium-236, and splits into barium-141, krypton-92, and three neutrons. |
| Why can fission create a chain reaction? | Each fission event can release neutrons that initiate fission in additional nuclei. |
| Critical mass | The minimum amount of fissionable material needed to sustain a nuclear chain reaction. |
| Subcritical mass | An amount of fissionable material below the amount needed to sustain a chain reaction. |
| Supercritical mass | An amount of fissionable material greater than critical mass, allowing a runaway chain reaction. |
| Four reactor controls named in the materials | Fuel limits, control rods, moderators, and cooling systems. |
| Function of control rods in a nuclear reactor | They absorb neutrons to control the fission rate. |
| Function of moderators in a nuclear reactor | Heavy water or graphite slows neutrons. |
| Function of cooling systems in a nuclear reactor | They remove and dissipate heat from the reactor core. |
| One advantage of nuclear fission power | A small amount of fissionable fuel can produce a very large amount of energy. |
| Major disadvantages of nuclear fission power | Radioactive waste disposal, accident risk, and thermal pollution. |
| Fusion reaction involving hydrogen isotopes | ²₁H + ³₁H -> ⁴₂He + ¹₀n. |
| Names of the two hydrogen isotopes used in the fusion example | Deuterium and tritium. |
| Why are extremely high temperatures needed for fusion? | They overcome electromagnetic repulsion between positively charged nuclei. |
| Approximate temperature in the notes needed to form plasma for fusion | About 40 million K. |
| Tokamak | A device that uses magnets to confine plasma in controlled fusion research. |
| Two advantages of fusion fuel and products | Hydrogen isotopes are abundant, and helium is the non-CO2 product. |
| Main challenge of controlled fusion | Obtaining more energy output than the energy input while sustaining the reaction. |
| Activity | The rate at which a radioactive sample decays, measured as disintegrations per unit time. |
| Becquerel (Bq) | One disintegration per second. |
| Gray (Gy) | Absorbed radiation dose; one joule per kilogram of tissue. |
| Sievert (Sv) | Effective radiation dose that accounts for biological effect. |
| Rad | A non-SI absorbed-dose unit equal to 0.01 J/kg of tissue. |
| Rem | A unit that accounts for radiation amount and the body’s sensitivity to its type. |
| Relationship among rem, rad, and RBE | rem = rad × RBE. |
| Relationship between sievert and rem | 1 Sv = 100 rem. |
| Relative biological effectiveness (RBE) | A measure of how effectively a type of radiation damages living tissue. |
| Why does alpha radiation have a higher RBE than beta radiation in the body? | Alpha particles transfer energy more efficiently and are more likely to damage tissue because they are larger. |
| Geiger counter | An instrument that detects and records ionizing radiation. |
| How does a Geiger counter produce a detectable signal? | Ionizing radiation ionizes argon gas, causing an electrical pulse that is registered and amplified. |
| Dosimeter | A device that measures the total radiation dose absorbed by a person. |
| Two forms of dosimeters named in the materials | Thermoluminescent crystal dosimeters and photographic film dosimeters. |
| Ionizing radiation | Radiation energetic enough to remove electrons from atoms or molecules. |
| What happens when gamma radiation ionizes water in tissue? | It removes an electron, forming reactive ions and hydroxyl free radicals. |
| Why are hydroxyl free radicals dangerous in living tissue? | They react with nearby biomolecules, create additional free radicals, disrupt cells, and damage tissue. |
| Why are fast-growing cells especially vulnerable to radiation? | They are more susceptible to radiation damage. |
| Acute radiation exposure | A high exposure over a short time, such as an accident. |
| Chronic radiation exposure | Lower or repeated exposure over a long time. |
| Somatic radiation damage | Damage directly to the exposed person’s body cells, such as burns or rashes. |
| Genetic radiation damage | Damage affecting reproductive cells that can lead to birth defects. |
| Why is radiation inside the body often especially dangerous? | It transfers energy efficiently to nearby cells and tissues. |
| Food irradiation purpose | Gamma irradiation kills bacteria that cause food spoilage. |
| Radiotracer | A radioisotope used to trace the path of an element through a chemical or biological system. |
| Iodine-131 use in medicine | Tracing thyroid function and treating thyroid cancer. |
| Iron-59 use as a radiotracer | Tracing red blood cells. |
| Phosphorus-32 use as a radiotracer | Studying eyes, liver, and tumors. |
| Sodium-24 use as a radiotracer | Tracing the circulatory system. |
| Technetium-99 use as a radiotracer | Studying the heart, bones, liver, and lungs. |
| Thallium-201 use as a radiotracer | Studying the heart and arteries. |
| Why is radon hazardous in a home? | It is colorless and odorless, can enter through foundation cracks, and its decay products can expose lung tissue to alpha radiation. |
| Radon source listed in the materials | The uranium decay series in bedrock. |
| Why does inhaled radon create greater risk than external alpha radiation? | Alpha particles are most harmful when their energy is deposited inside the body, especially in the lungs. |
| Three traditional cancer-treatment strategies | Radiation therapy, chemotherapy, and surgery. |
| Why can radiation be used to treat cancer? | Cancer cells grow rapidly and are especially susceptible to radiation damage. |
| Immunotherapy approach named in the materials | CAR-T cell therapy, using chimeric antigen receptor cells. |
| How was nuclear fission discovered? | Fermi bombarded uranium; Hahn and Strassmann detected barium and krypton; Meitner concluded that uranium-235 had split. |
| Why is rem a better biological-dose measure than curie? | Rem accounts for absorbed dose and relative biological effectiveness, while curie measures only activity. |
Created by:
mollyig