History of Atomic Structure

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

A. Thousands of years

B. Hundreds of years

C.A few years

D.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.

Aristotle

Democritus

Alchemists• 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.

Niels Bohr

Bohr’s Model

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 TimelineRequirements:• Must include a title.• Must include a spot for each of the 7 items.• Must include at least the Who, When, and

What.• Must have a picture for each item – see

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