History of atomic structure
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History of Atomic Structure. How long have people been interested in understanding matter and its structure? Thousands of years Hundreds of years A few years Never. Ancient Philosophy. Who: Aristotle, Democritus When: More than 2000 years ago Where: Greece

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History of Atomic Structure

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History of Atomic Structure

How long have people been interested in understanding matter and its structure?

  • Thousands of years

  • Hundreds of years

  • A few years

  • Never

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 reasoning to explain the existence of everything.




  • Who: Early “Scientists”

  • When: 500 – 900 years ago

  • Where: Europe, Asia and Middle East

  • What: Their work developed into what is now modern chemistry.

  • Why: Trying to change ordinary materials into gold.

Alchemic Symbols

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.

John Dalton

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. ‘Plum pudding’ model.

  • Why:Thompson knew atoms were neutrally charged, but couldn’t find the positive particle.

J. J. Thompson

‘Solar system’ model

  • 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.

Ernest Rutherford – born in NZ

Orbits model

  • 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.

Bohr’s Model

Niels Bohr

Electron cloud model

  • 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 cloud model

What is the latest?

  • Scientists have discovered many new smaller parts of an atom.

  • Find out more!!!!!

Atomic Structure Timeline


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