Bellwork 101206 How long have people been interested

Bellwork 10/12/06 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

History of Atomic Structure

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.

Democritus Aristotle

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.

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

J. J. Thompson

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.

Ernest Rutherford

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.

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

Atomic Structure Timeline Requirements: • 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 (color is preferred) for each item. Options: • Comic book format • Standard timeline