Comprehensive Notes: Concept of Atomic Number and Synthesis of New Elements in the Laboratory

Concept: Atomic Number and Synthesis of New Elements in the Laboratory

• This module for Physical Science Grade 11 (ADM) focuses on how the atomic number leads to the synthesis of new elements in the laboratory and the broader context of nucleosynthesis.
• Core idea: the atomic number Z (the number of protons) largely determines an element’s identity and properties; synthesis of new elements involves nuclear reactions that change Z (and A, the mass number).

Key Concepts and Definitions

• Atomic number (Z): the number of protons in an atom’s nucleus; determines the element’s identity and most properties.
  • Expressed as Z = number of protons.
  • Illustrative statement from Moseley: X-ray emission frequencies scale with the nuclear charge; this linked chemical properties to the actual count of protons rather than atomic weight alone.
• Atomic weight vs. atomic number (historical context):
  • Dmitri Mendeleev arranged elements by atomic weight (numerical order) and predicted gaps.
  • Henry Moseley showed that using atomic number (Z) better predicts periodic trends; gaps at Z = 43, 61, 85, 87 correspond to elements later synthesized (Tc, Pm, At, Fr).
• Nuclear transmutation (concept of transforming one element into another):
  • 1919: Ernest Rutherford performed artificial nuclear transmutation; foundational example of transforming one nuclide into another.
  • 1932: James Chadwick discovered the neutron, enabling neutron-induced transmutation and reactor-based synthesis.
• Particle accelerators and related devices:
  • Purpose: speed up charged particles (e.g., protons, deuterons) to overcome electrostatic repulsion with target nuclei, enabling nuclear reactions.
  • Examples: particle accelerators and cyclotrons; used to synthesize new elements by bombarding target nuclei with high-energy projectiles.
  • Example reaction (conceptual): $^{97}<em>{42} ext{Mo} + ^{2}</em>{1} ext{H} <br /> ightarrow ^{97}<em>{43} ext{Tc} + ^{1}</em>{0} ext{n}$
• Notable artificial/natural discoveries tied to atomic-number–driven synthesis:
  • Technetium (Tc, Z = 43) — first element synthesized in the lab (1937, Segre and Perrier by bombarding molybdenum with deuterons).
  • Astatine (At, Z = 85) — discovered in 1940 by bombarding bismuth with alpha particles; name derives from the Greek for unstable.
  • Promethium (Pm, Z = 61) and Francium (Fr, Z = 87) discovered as products of uranium fission or decay series.
  • Neptunium (Np, Z = 93) and Plutonium (Pu, Z = 94) discovered in the 1940s as transuranic elements; early transuranics produced in reactors or accelerators.
• Transuranic elements and superheavy elements:
  • Transuranic elements: atomic number Z > 92 (beyond uranium).
  • Neptunium (93) and Plutonium (94) as early transuranics; many later transuranics discovered via reactors or accelerators.
  • Superheavy elements: elements with Z > 103; produced via high-energy collisions using accelerators and heavy targets (e.g., Bohrium Z = 107).
• Nuclear reactions and notation (typical examples in this module):
  • Be-9 + He-4 → C-12 + n (a representative light-nucleus reaction)
  • 14N + 4He → 17O + 1H (nuclear reaction used to illustrate transmutation and neutron/proton balance)
  • Mo-97 + H-2 (deuteron) → Tc-97 + n (example of Mo + deuteron yielding Tc and a neutron)
• Key historical milestones (in brief):
  • 1913: Moseley’s work linking atomic number to X-ray frequencies and element properties.
  • 1919: Rutherford’s nuclear transmutation experiments; first artificial preparation of a nuclide (e.g., ^{17}O).
  • 1932: Chadwick discovers the neutron.
  • 1937: First synthesis of technetium by Segre and Perrier via Mo bombardment with deuterons.
  • 1942: First controlled nuclear chain reaction (Chicago Pile-1) demonstrating a sustained fission reaction.
  • 1940s: Discovery of astatine and promethium; neptunium and plutonium follow in rapid succession.
  • 1950s–60s+: Development of cyclotron and other accelerators enabling transmutation and synthesis of heavier elements.

Historical Experiments and Key Discoveries (Condensed timeline)

• 14N + 4He → 17O + 1H: Rutherford-style demonstration of nuclear transmutation; first artificially prepared nuclide 17O.
• 9Be + 4He → 12C + n: example of alpha particle-induced reactions yielding stable carbon and neutrons (x-ray spectroscopy and reaction studies underpinting the method).
• 1919 Rutherford transmutation: transformation of one element or isotope into another; foundational for synthetic elements.
• 1932 Chadwick: discovery of neutron; essential for neutron-induced reactions and reactor physics.
• 1937 Segre and Perrier: bombardment of Mo with deuterons to produce Technetium (Tc, Z = 43); first synthetic element.
• 1940: Promethium (Pm, Z = 61) and Francium (Fr, Z = 87) discoveries tied to uranium decay and fission products; astatine (At, Z = 85) discovered via cyclotron methods.
• 1942: First controlled nuclear chain reaction at University of Chicago; example reaction chains involved in fission of heavy nuclei such as uranium.
• 1940s: Neptunium (Np, Z = 93) and Plutonium (Pu, Z = 94) synthesized in reactors/cyclotrons; foundational for nuclear chemistry and energy applications.
• 1950s–60s: Cyclotron and large-scale accelerators enable synthesis of heavier elements; cyclotron-driven transmutation is emphasized as a key milestone.

Big Bang Nucleosynthesis and Stellar Nucleosynthesis

• Big Bang Nucleosynthesis (BBN) overview:
  • Key stages: Singularity, Inflation, Nucleosynthesis, Recombination.
  • Singularity: a one-dimensional point with infinite density and gravity; physics as we know it ceases to operate.
  • Inflation: homogenizes matter distribution; sets the stage for subsequent nucleosynthesis.
  • Nucleosynthesis: nuclear fusion forming new nuclei in the early universe.
  • Recombination: capture of free electrons by ions in the plasma, leading to neutral atoms.
• Observational notes:
  • Oldest stars show low abundances of elements heavier than helium; Fe/H is about 10^(-5) to 10^(-6) of solar values (text notes ~130,000 times smaller than solar).
  • Current astronomical data are approaching primordial abundances for light elements but still not matched exactly.
• Stellar nucleosynthesis (how stars build elements):
  • Low-mass stars: synthesize He, C, O during main-sequence, red giant branch (RGB), horizontal branch (HB), asymptotic giant branch (AGB); elements are mixed to surface via convection and ejected via stellar winds and planetary nebulae.
  • Higher-mass stars: deeper fusion cycles produce elements up to iron (Fe) via successive fusion reactions.
  • Ejecta (winds and supernova explosions) distribute newly created elements into the interstellar medium for incorporation into later generations of stars.
• Elements heavier than iron (Fe):
  • Light-element fusion becomes energetically unfavorable beyond Fe; non-equilibrium processes can create heavier (often radioactive, sometimes stable) nuclei beyond Fe.
  • Two principal neutron-capture paths build heavier elements: S-process (slow) and R-process (rapid).

S-process and R-process (Neutron Capture Nucleosynthesis)

• S-process (Slow neutron capture)
  • Mechanism: nuclei capture neutrons slowly enough that beta decay can occur between captures, moving up one element at a time.
  • Timescale: neutron captures are slow compared with beta-decay timescales (can be years to centuries between captures in some stellar interiors).
  • Range: operates up to around element 83 (Bismuth, Bi).
  • Observational peaks: Sr (38), Ba (56), Pb (82) reflect magic numbers and abundance peaks.
  • Site: AGB stars during shell flashes; neutron source primarily via the reaction $^{13}<em>{6}C + ^{4}</em>{2}He <br /> ightarrow ^{16}<em>{8}O + ^{1}</em>{0}n$ (a by-product of C-13 and He-4 fusion).
• R-process (Rapid neutron capture)
  • Mechanism: a large flux of neutrons leads to rapid neutron captures before beta decays can occur, pushing nuclei far from stability.
  • Site: core-collapse supernovae (SN II) and other environments with intense neutron fluxes (e.g., neutron star mergers in more modern discussions).
  • Evolution: after a rapid build-up of a very heavy isotope, successive beta decays increase the atomic number, producing very heavy, neutron-rich nuclei.
  • Evidence: heavy elements associated with early Galactic chemical enrichment point to SN II as important sources of r-process material; abundance patterns observed in old stars support r-process production.
• Practical notes from the module:
  • S-process can produce elements up to Z ≈ 83 (Bi) with characteristic abundance peaks linked to neutron-shell (magic) numbers.
  • R-process yields include some of the heaviest elements and require explosive, neutron-rich environments.

Transuranic and Superheavy Elements

• Transuranic elements: elements with atomic numbers beyond 92 (Uranium).
  • Notable examples: Neptunium (Z = 93), Plutonium (Z = 94).
  • Production: typically synthesized in nuclear reactors or particle accelerators.
• Early transuranics and discovery timeline:
  • 1930s–1940s: transuranics were discovered through artificial production methods (neutron bombardment and deuteron/accelerator methods).
• Superheavy elements (Z > 103):
  • Produced by bombarding heavy nuclei with accelerated heavy projectiles.
  • Example historically cited: Bohrium (Z = 107) produced using a chromium projectile.
• Representative nuclear reactions (as given in the module):
  • $^{97}<em>{42}Mo + ^{2}</em>{1}H <br /> ightarrow ^{97}<em>{43}Tc + ^{1}</em>{0}n$
  • $^{9}<em>{4}Be + ^{4}</em>{2}He <br /> ightarrow ^{12}<em>{6}C + ^{1}</em>{0}n$
• Notable transuranics (contextual):
  • Neptunium (Np, Z = 93) discovered in the 1940s; Plutonium (Pu, Z = 94) discovered shortly after.
  • These elements are unstable and decay radioactively into lighter elements.
• Future directions: continued exploration of the “island of stability” and synthesis of heavier superheavy elements with improved lifetimes and more detailed chemical exploration.

Practical Activities and Assessments (From the Module)

• What I Need to Know (Learning goals):
  • Explain how the concept of atomic number led to synthesis of new elements in the lab.
  • Identify elements formed after synthesis.
  • Recognize the importance of atomic number in identifying identity on the periodic table.
• What I Know / What’s In / What’s New / What Is It / What’s More / What I Have Learned / What I Can Do / Assessments:
  • The module includes guided activities, independent activities, and an answer key to self-check.
  • A “Make Your Own Periodic Table” activity is included as an interactive exercise (subject to student clues and symbol arrangement).
• Answer Key and Assessment items (highlights):
  • The module includes multiple-choice questions (e.g., identifying accelerators, key scientists, and concepts like nucleosynthesis, S-process, R-process, etc.).
  • Example answers (as provided in the included Answer Key):
  • 1. c
  • 2. d
  • 3. c
  • 4. c
  • 5. b
  • 6. a
  • 7. b
  • 8. c
  • 9. c
  • 10. a
  • 11. a
  • 12. b
  • 13. d
  • 14. c
  • 15. ? (Not fully filled in the provided key)
• Practical activities proposed:
  • Write nuclear reactions for the synthesis of named elements (e.g., Curium, Mendelevium, Meitnerium) as per activity prompts.
  • Research latest instruments used to prepare new elements (Nihonium, Moscovium, Tennessine, Oganesson).
  • Timeline activity: create a timeline illustrating how elements form with respect to atomic number; rubrics provided for content accuracy, graphics, readability, and completeness.
• Timeline rubrics (key criteria):
  • Content accuracy; number of events; graphic balance; readability; number of events (10 maximum for ideal score).

Worked Examples and Important Equations (LaTeX)

• Atomic number definition:
  • $Z = ext{number of protons in the nucleus}$
• Relationship noted by Moseley (conceptual):
  • The frequency of X-ray emission is related to the nuclear charge; the law underpinning this relationship relates to the square root of frequency: $ext{frequency} ext{ f} <br /> ightarrow ext{proportional to } Z^2 ext{ in Moseley’s observations (conceptual)}.$
• Representative nuclear reaction examples from the module:
  • $^{14}<em>{7}N + ^{4}</em>{2}He <br /> ightarrow ^{17}<em>{8}O + ^{1}</em>{1}H$
  • $^{9}<em>{4}Be + ^{4}</em>{2}He <br /> ightarrow ^{12}<em>{6}C + ^{1}</em>{0}n$
  • $^{97}<em>{42}Mo + ^{2}</em>{1}H <br /> ightarrow ^{97}<em>{43}Tc + ^{1}</em>{0}n$
• Big Bang and nucleosynthesis (conceptual):
  • Singularity, Inflation, Nucleosynthesis, Recombination (stages of early universe evolution).
• S-process and R-process (conceptual summaries):
  • S-process: neutron capture followed by beta decay in slow succession; produces up to Bi (Z = 83).
  • R-process: rapid neutron captures in high-neutron-flux environments (e.g., SN II); produces very heavy elements beyond Fe.

Connections to Foundational Principles and Real-World Relevance

• Atomic number as the fingerprint of an element connects to periodic trends and element identity; Moseley’s work realigned the periodic table with authoritative physical measurements rather than purely chemical or weight-based organization.
• Nuclear transmutation and element synthesis in laboratories underpin modern nuclear chemistry, medical isotopes, and energy research; understanding Z and neutron capture processes explains why some elements exist only in trace amounts and why others are produced in labs.
• S-process and R-process provide a framework for interpreting observed elemental abundances in stars and in the interstellar medium, connecting astrophysics with nuclear physics and observational astronomy.
• The story of transuranic and superheavy elements reflects the limits of chemical separations and the challenges of creating and characterizing extremely short-lived species, underscoring the interplay between experimental technique and theory.
• Ethical and practical implications: synthesis of new elements generally involves high-energy physics, radiation hazards, and regulatory oversight; the module emphasizes responsible lab practices and safety.

Connections to Previous/Foundational Principles

• Periodic table organization (Mendeleev’s weight-based view vs Moseley’s Z-based view).
• Nuclear physics concepts: alpha/beta decay, neutron capture, fission, and transmutation.
• Fusion vs fission concepts in astrophysical and terrestrial settings.
• The role of accelerators and reactors in producing new elements and in energy applications.

References and Further Reading (as listed in the module)

• Coyne, Glynis L. (2012). Lead to Gold, Sorcery to Science: Alchemy and the Foundations of Modern Chemistry. University of North Carolina PIT Journal, 4.
• Famous Scientist: Henry Moseley. famouscientist.org, 2014.
• Gonzales, Jay. “Synthesis of the New Elements in the Laboratory.” SlideShare, 2017.
• “Henry Moseley, the Atomic Number, and Synthesis of Elements.” Teach Together, 2012.
• Navarro, Mary Grace. “The Atomic Number and the Synthesis of New Elements.” Academia, 2020.
• “The Synthesis of the Elements.” Lick Observatory (PDF).