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ATOMOS, ARISTOTLE AND ALCHEMY (CHEMISTRY BEFORE MODERN HISTORY)
PHYSICAL SCIENCE
AGENDA
Objective: At the end of the lesson, the learners will be able to:
Discuss key developments in the concept of the atom and element throughout pre-modern history.
Discuss key developments in the practical application of chemistry throughout pre-modern history.
Articulate the contributions of alchemy as a protoscience to chemistry.
ATOMISM AND NON-ATOMISTIC VIEWS OF THE GREEKS
Key Figures: Leucippus and Democritus
Context: Physicists in Ancient Greece.
Key Ideas of Atomism:
Atomism posits that matter is composed of indivisible particles called atoms.
Features of Atomism:
Atoms make up most of the universe; empty space (void) exists where there are no atoms.
Atoms are solid, homogeneous, and indivisible (from the Greek term "atomos," meaning uncuttable).
The motion and collision of atoms in empty space cause observable changes in the universe.
Characteristics of matter are influenced by the shapes, sizes, and weights of atoms.
Example: Sharp atoms cause tearing sensations on the tongue and create sour or bitter tastes.
Atoms in clay have flexible connections that harden when baked.
Atomism was more philosophical than scientific but aligned closely with modern material concepts.
However, it faced opposition from prominent philosophers and was later deemed heretical by religious groups for denying God’s existence.
Greek Philosophers’ Views on Matter
Anaxagoras: Argued for an infinite number of elementary natural substances composed of minuscule particles leading to various forms in the universe.
Empedocles: Suggested everything is composed of four eternal and unchanging kinds of matter: Fire, Air (gases), Water (liquids and metals), and Earth (solids).
Plato: Expanded on Empedocles’ theory by associating the four elements with geometric solids (Platonic Solids) divisible into triangles, leading to different combinations and apparent transformations of matter.
Aristotle: Believed in an infinite number of combinations of the four elements leading to varying proportions of "essential qualities," primarily hot, dry, and cold.
ALCHEMY ACROSS CIVILIZATIONS
Alchemy’s practical aspects flourished in various civilizations despite limited advancements in conceptualizing matter during this period:
Mesopotamians: Utilized metals like gold and copper and matched symbols with heavenly bodies. Used dyes, glass, paints, and perfumes.
Egyptians: Adapted techniques from Mesopotamians, perfecting the use of bronze and dyes, which influenced Greek practices.
Chinese: Developed metalworking and ceramics, focusing on minerals and substances for longevity. Some medicinal substances showed positive effects, while others like Mercury were harmful.
Indians: Engaged in alchemy (Rasayana) linked closely to Vedic medicine and Hindu/Buddhist beliefs. Invented dye, glass, cement, soap, and iron/steel.
Arabs and Muslims: Enriched alchemical practices and literature, notably Jabir ibn Hayyan (Geber), who translated Greek Aristotelian practices, wrote on metal purification, and developed acids like nitric, hydrochloric, and sulfuric acid, as well as aqua regia.
MYSTICISM AND PROGRESS IN ALCHEMY
Despite many practical advances, alchemy was often intertwined with mysticism and trial and error, referred to historically as alchemy (Arabic/Greek: Alkimiyā - "the art of transmuting").
Influences:
Aristotle’s ideas on elements combined with methods developed by various civilizations.
Goals of alchemists:
Transform base metals (e.g., lead, iron) into purer metals (silver, gold).
Discover the "Philosopher's Stone" and the "Elixir of Life."
Alchemy as both a contributor to and a hindrance for scientific thought is distinguished in a T-chart:
Scientific Contributions:
Refined techniques for crystallization, condensation, and distillation.
Investigated properties of elements like phosphorus and sulfur.
Developed systematic procedures and equipment.
Unscientific Contributions:
Incorporated incantations, magic, and esoteric symbols linked to astrology and religion.
Focused on wealth and purity rather than empirical study.
ALCHEMY AS PROTOSCIENCE
Alchemy is viewed as a protoscience due to its foundational role despite misconceptions:
Protoscience: An unscientific field of study which later developed into real science (e.g., astrology into astronomy, alchemy into chemistry).
LATER DEVELOPMENTS IN ATOMIC STRUCTURE
THE STRUCTURE OF THE ATOM
A new set of lessons will address the foundational changes in understanding atomic theory post-Dalton.
Key Learning Outcomes:
Key developments in the atomic structure concept.
Brief explanations of the various atomic models.
JOHN DALTON’S ATOMIC THEORY
Context: Before Dalton, atomistic beliefs were centered on indivisible particles (Billiard Ball Model).
Dalton established the atom was:
Fundamental, indestructible, and invisible; a standard model of atomic theory.
ROBERT BROWN AND BROWNIAN MOTION
Observation: Brown discovered pollen grains in water exhibit irregular, jittery motion (Brownian Motion).
Significance: This phenomenon became crucial for future research by scientists including Albert Einstein and Jean Perrin, providing mathematical and experimental validation for atomic theory.
JOSEPH JOHN THOMSON
Contributions:
Introduced the Plum Pudding Model in 1904, suggesting:
The atom is a sphere of positive charge with embedded electrons.
Experiments: Worked with cathode rays, discovering electrons.
Proposed that electrons were not the only source of mass, hinting at the presence of other atomic structures.
ERNEST RUTHERFORD
A student of Thomson who explored radioactivity and developed the idea of an atomic nucleus:
Observations: Through α and β radiation experiments, he discerned changes on a subatomic level.
His gold foil experiment led to the Rutherford model of the atom, visualizing electrons orbiting around a dense, positively charged nucleus (solar system analogy).
NIELS BOHR
Addressed instability in Rutherford's model by proposing quantized energy levels for electrons (Bohr model, 1913):
Introduced the concept that electrons can only exist in specific energy levels and that they can jump between these levels by absorbing or releasing energy.
QUANTUM MODELS OF THE ATOM
Based on ideas from Heisenberg and Schrödinger:
Conceptual Advances: Electrons exhibit properties of both waves and particles, leading to the concept of orbitals rather than fixed orbits.
Defined regions of space with varying probabilities of finding electrons (electron clouds).
JAMES CHADWICK
Discovered neutrons in 1926, confirming their role in the atomic structure and leading to a comprehensive understanding of isotopes and nuclear reactions.
HENRY MOSELY, ATOMIC NUMBER, AND SYNTHESIS OF ELEMENTS
HENRY MOSELY
Background: Researcher in Rutherford’s lab, made significant contributions in 1913 by:
Noticing the relationship between x-ray frequency emissions and atomic charge when electrons struck elements.
Developed X-ray spectroscopy, which improved the arrangement of elements, correcting Mendeleev’s periodic table.
SYNTHESIS OF ELEMENTS
Cyclotron Development: Enabled transmutation of elements and the artificial creation of heavier elements, e.g., technetium (first artificial element) from molybdenum via nuclear reactions.
Example Reaction:
Transuranic Elements: Synthetic elements beyond Uranium (Z=92), e.g., Neptunium (Z=93) and Plutonium (Z=94), confirm artificial synthesis methods.
Superheavy Elements: Elements with atomic numbers above 103 produced by colliding heavy nuclear targets using accelerated projectiles.
Example Reaction for Bohrium (Z = 107):