History of Atomic Structure. Ancient Philosophy Who: Aristotle, Democritus When: More than 2000...
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Transcript of History of Atomic Structure. Ancient Philosophy Who: Aristotle, Democritus When: More than 2000...
Ancient Philosophy• Who: Aristotle, Democritus
• When: More than 2000 years ago
• Where: Greece
• What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles he named “atoms”.
• Why: Aristotle and Democritus used observation and inferrence to explain the existence of everything.
Alchemists• Who: European Scientists
• When: 800 – 900 years ago
• Where: Europe
• What: Their work developed into what is now modern chemistry.
• Why: Trying to change ordinary materials into gold.
Particle Theory• Who: John Dalton
• When: 1808
• Where: England
• What: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom.
• Why: Building on the ideas of Democritus in ancient Greece.
Discovery of Electrons• Who: J. J. Thompson
• When: 1897
• Where: England
• What: Thompson discovered that electrons were smaller particles of an atom and were negatively charged.
• Why: Thompson knew atoms were neutrally charged, but couldn’t find the positive particle.
Electron Charge and Mass• Who: Robert A. Millikan (1868-1953)• When:1910• Where: United States• What: Found the quantity of an electron charge in
his oil-drop experiment. He calculated the charge by suspending negatively charged oil droplets between two plates and measure the rate of fall when the voltage was changed.
• Why: Wanted to discover whether electrical charge occurred in a specific amount.
Atomic Structure I• Who: Ernest Rutherford
• When: 1911
• Where: England
• What: Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core.
• Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged.
Atomic Structure II• Who: Niels Bohr
• When: 1913
• Where: England
• What: Proposed that electrons traveled in fixed paths around the nucleus. Scientists still use the Bohr model to show the number of electrons in each orbit around the nucleus.
• Why: Bohr was trying to show why the negative electrons were not sucked into the nucleus of the atom.
Electron Cloud Model-1920s• Electrons travel around the nucleus in
random orbits.
• Scientists cannot predict where they will be at any given moment.
• Electrons travel so fast, they appear to form a “cloud” around the nucleus.
Electron Orbitals• Who: Erwin Schrödinger
• When: 1926
• Where: Austria
• What: Develops mathematical equations to describe the motion of electrons in atoms, which leads to the quantum mechanical model
• Why: Wanted to better understand the movement of the electrons in an atom
Birth of Quantum Mechanics: • Who: Werner Heizenberg • When: 1925• Where: Germany• What: Proposed that electrons traveled in
atomic orbitials• Why: Heizenberg realized that the reason
Bohr’s model failed was that it was trying to predict none observable variables (position, speed)