Questions and Answers
Who proposed that atoms are solid indivisible spheres?
The Plum Pudding model was proposed by Joseph John Thomson.
True
What experiment did Robert Millikan conduct to determine the charge of electrons?
Oil-drop Experiment
H.G.J. Moseley studied _____ given off by various elements to establish atomic numbers.
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Match the following scientists with their contributions to atomic theory:
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What does the atomic number of an element represent?
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Niels Bohr proposed that electrons can occupy an infinite number of energy levels.
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Who discovered neutrons?
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The principle that states it is impossible to determine the exact momentum and position of an electron simultaneously is known as the ______.
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Match the following individuals to their contributions to atomic theory:
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Study Notes
Early Theoretical Foundations
- Leucippus and Democritus introduced the concept of "Atomos," meaning uncuttable, proposing atoms as solid, indivisible spheres.
- Aristotle and contemporaries argued matter was composed of four elements: earth, water, air, and fire.
Dalton's Atomic Theory
- John Dalton (1807) presented the Solid Sphere Model, depicting atoms as solid spheres, though acknowledging they are not indivisible.
Discovery of Electrons
- Humphry Davy (1800s) studied chemical compounds, revealing that electrical forces hold elements together.
- Michael Faraday (1832) established a relationship between electricity used in electrolysis and chemical reaction extent.
- George Stoney (1891) proposed the term "electrons" for electric ions.
Cathode-Ray Tube Experiment
- Joseph John Thomson (1897) conducted groundbreaking experiments, providing strong evidence for the existence of electrons, developing the Plum Pudding Model.
- Robert Millikan (1909) performed the Oil-drop Experiment, determining the charge of electrons.
Further Developments in Atomic Structure
- Hantaro Nagaoka (1903) introduced the Saturn-like model of the atom.
Discovery of Protons
- Eugen Goldstein (1886) used the Canal Rays Experiment to identify positively charged particles in cathode-ray tubes, termed positive ions.
- Ernest Rutherford (1910) conducted the Scattering Experiment, challenging Thomson's model by demonstrating that most alpha particles pass through gold foil with minimal deflection, concluding that atoms possess small, dense positively charged nuclei.
Atomic Number Concept
- H.G.J. Moseley (1913) determined that the identity of an element is based on the atomic number, defined as the number of protons in the nucleus.
Discovery of Neutrons
- J. Chadwick (1932) identified neutrons through beryllium bombardment with high-energy alpha particles.
Bohr's Model of the Atom
- Niels Bohr described hydrogen atom electrons as revolving in discrete circular orbits, leading to Bohr's Planetary Model.
- Defined energy levels correspond to orbits; electron excitation involves absorption of quantized energy.
Wave Nature of Electrons
- Louis de Broglie proposed electrons exhibit wave-like properties, suggesting they should be modeled as waves rather than compact particles.
Quantum Mechanics
- Quantum mechanics elaborates on matter's wave properties; Werner Heisenberg formulated the Uncertainty Principle (1927), highlighting the impossibility of precisely determining both momentum and position of an electron simultaneously.
- Erwin Schrödinger formulated the Wave Equation to estimate electron positions and quantify their energy levels.
Modern Atomic Model
- The Electron Cloud Model, created by Schrödinger, describes atomic orbitals as regions of probability for finding an electron, representing the Quantum Mechanical Model of the atom.
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Description
Explore the foundational concepts of atomic theory from ancient Greek philosophers like Leucippus and Democritus to John Dalton's solid sphere model. This quiz covers the evolution of atomic ideas and the contributions of prominent scientists throughout history. Test your knowledge on how the perception of atoms has changed over time.
