Chemistry
25 flashcards
~13 min
Nuclear Chemistry and Radioactivity
Explore the fascinating world of atomic nuclei with this comprehensive nuclear chemistry flashcard deck. Nuclear chemistry deals with reactions that change the nucleus itself — releasing millions of times more energy than ordinary chemical reactions. It underp...
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Explore the fascinating world of atomic nuclei with this comprehensive nuclear chemistry flashcard deck. Nuclear chemistry deals with reactions that change the nucleus itself — releasing millions of times more energy than ordinary chemical reactions. It underpins nuclear power, medical imaging (PET scans, X-rays), cancer radiation therapy, radiocarbon dating, and nuclear weapons. This deck covers the structure of the nucleus, types of radioactive decay (alpha, beta, gamma), balancing nuclear equations, radioactive decay laws and half-life calculations, radiocarbon dating, nuclear fission and chain reactions, nuclear fusion, binding energy and mass defect, and radiation safety. Essential for AP Chemistry, A-Level, and university general chemistry.
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The spontaneous emission of radiation from an unstable atomic nucleus as it decays toward a more stable configuration. The rate of decay is not affected by temperature, pressure, or chemical state.
Emission of an alpha particle = 2 protons + 2 neutrons (identical to a helium-4 nucleus, ⁴₂He). Nucleus loses 2 protons and 2 neutrons. Low penetration — stopped by paper or skin. Highly ionizing. Most dangerous if inhaled/ingested.
Emission of a beta particle = a fast-moving electron (β⁻) from the nucleus when a neutron converts to a proton: n → p + e⁻ + antineutrino. Nucleus gains 1 proton. Penetrates skin; stopped by aluminium foil.
High-energy electromagnetic radiation emitted from the nucleus, often following alpha or beta decay. No change in atomic number or mass number. Highly penetrating — requires thick lead or concrete shielding. Least ionizing.
The sum of mass numbers (A, top) and the sum of atomic numbers (Z, bottom) must be equal on both sides of the equation. Example: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He. (238=234+4 ✓ and 92=90+2 ✓)
The time taken for half the radioactive atoms in a sample to decay. It is constant for a given isotope. After n half-lives: N = N₀ × (½)ⁿ or m = m₀ × (½)^(t/t½).
N(t) = N₀ e^(−λt) where N₀ = initial number of atoms, λ = decay constant (s⁻¹), t = time. The decay constant λ = ln2 / t½ = 0.693 / t½. First-order kinetics — same mathematics as first-order chemical reactions.
Uses the known half-life of ¹⁴C (5,730 years) to date organic materials up to ~50,000 years old. Living organisms maintain a constant ¹⁴C/¹²C ratio. After death, ¹⁴C decays without replacement. Measuring the ratio determines the age.
The splitting of a heavy nucleus (e.g., ²³⁵U or ²³⁹Pu) into two smaller nuclei when struck by a neutron, releasing a large amount of energy and 2–3 more neutrons. These neutrons can trigger further fissions — a chain reaction.
A chain reaction occurs when neutrons from one fission event cause additional fissions. Critical mass: The minimum mass of fissile material needed to sustain a self-sustaining chain reaction. Above critical mass → uncontrolled reaction (nuclear explosion).
The combination of two light nuclei (e.g., deuterium and tritium, isotopes of hydrogen) to form a heavier nucleus, releasing enormous energy. Powers the Sun and hydrogen bombs. Requires extremely high temperatures (~10⁷–10⁸ K) to overcome electrostatic repulsion.
Mass defect: The difference between the mass of a nucleus and the sum of masses of its constituent protons and neutrons. Binding energy: Energy equivalent of mass defect (E=mc²). Higher binding energy per nucleon = more stable nucleus. Iron-56 has the highest binding energy per nucleon.
Albert Einstein's mass-energy equivalence equation: energy (E) equals mass (m) times the speed of light squared (c² = 9×10¹⁶ m²/s²). In nuclear reactions, small mass changes release enormous energy. Used to calculate binding energy from mass defect.
Atoms of the same element with the same number of protons but different numbers of neutrons — and therefore different mass numbers. Example: ¹²C (6p, 6n), ¹³C (6p, 7n), ¹⁴C (6p, 8n). Some isotopes are stable; others are radioactive.
ᴬzX where A = mass number (protons + neutrons), Z = atomic number (protons), X = element symbol. Example: ²³⁵₉₂U = Uranium with 92 protons, 235 total nucleons, and 143 neutrons.
Alpha (α): Stopped by paper, skin, or a few cm of air. Beta (β): Stopped by a few mm of aluminium. Gamma (γ): Requires several cm of lead or meters of concrete. Ionizing power is the reverse order: α > β > γ.
A proton converts to a neutron: p → n + e⁺ + neutrino. A positron (β⁺) — the antimatter equivalent of an electron — is emitted. Atomic number decreases by 1. Used in PET (Positron Emission Tomography) scans.
A nucleus captures an inner-shell electron, converting a proton to a neutron: p + e⁻ → n + neutrino. Atomic number decreases by 1. Competes with positron emission for proton-rich nuclei.
A controlled nuclear fission device. Fuel: Enriched uranium (²³⁵U). Moderator (e.g., water, graphite): Slows neutrons to sustain chain reaction. Control rods (e.g., boron, cadmium): Absorb neutrons to control reaction rate. Coolant: Transfers heat to generate steam and electricity.
Byproducts of nuclear reactions that remain radioactive for varying periods. Low-level waste: Clothing, tools — short-lived. Intermediate-level waste: Reactor components. High-level waste: Spent fuel rods — remain dangerous for thousands of years; stored in deep geological repositories.
PET scan: ¹⁸F-fluorodeoxyglucose detects cancer. MRI contrast: Gadolinium. Thyroid treatment: ¹³¹I (iodine-131). Bone scans: ⁹⁹ᵐTc (technetium-99m — most used medical isotope). Cancer radiotherapy: High-energy γ radiation from cobalt-60.
A graph of neutron number (N) vs proton number (Z) showing which nuclei are stable. Stable nuclei lie in the "valley." Above the valley (too many neutrons): β⁻ decay. Below (too few neutrons): β⁺ decay or electron capture. Very heavy nuclei: α decay.
Natural uranium is ~99.3% ²³⁸U and only ~0.7% fissile ²³⁵U. Enrichment increases the ²³⁵U proportion. Reactor-grade: 3–5% ²³⁵U. Weapons-grade: >90% ²³⁵U. Done by gaseous diffusion or centrifuge separation.
An instrument used to detect and measure ionizing radiation (α, β, γ). Radiation ionizes gas inside the tube, creating a current pulse that is counted. Measures activity in counts per second (cps) or Becquerels (Bq).
Becquerel (Bq): 1 decay per second (activity). Gray (Gy): Energy absorbed per kg of tissue (absorbed dose). Sievert (Sv): Dose equivalent — accounts for biological damage potential of different radiation types. 1 Sv = 1 Gy × radiation weighting factor.