WHAT IS MATTER MADE OF?

5 THEORIES OF MATTER 1. Fire, air, water and earth 2. Tiny, solid particles called atoms 3. Lumps of positively charged material with negative electrons all through it 3. A positive nucleus with negative electrons moving around it 5. A positive nucleus with electrons orbiting around it

WHAT IS MATTER MADE OF? Empedocles was a Greek philosopher and scientist He said that matter is made of:

Why might that make sense to people who knew nothing about atoms?

(greek for indivisible) HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible)

SO WHAT IS MATTER MADE OF? John Dalton, who lived in the early 1800s, said: Matter is made up of tiny particles called atoms Atoms can’t be created, or destroyed All atoms of the same element are identical and are different from atoms of all other elements Different elements link together, in defined whole number ratios, to make compounds Dalton’s atom Atoms are the smallest particles and don’t have distinct parts

John Dalton, who lived in the early 1800s, said: 1. Matter is made up of tiny particles called atoms http://www.youtube.com/watch?v=1xSQlwWGT8M&feature=fvwrel Introduction to the Atom @ http://www.khanacademy.org/

Dalton also said: 2. Atoms cannot be created or destroyed CREATED

3. All Elements have Unique Atoms Dalton also said: 3. All Elements have Unique Atoms Lithium Gold Uranium Sodium Hydrogen

Dalton also said: 4. Elements combine in defined, whole number ratios H2O – water vs. not H2O – water oxygen ¾ oxygen hydrogen ½ hydrogen oxygen hydrogen hydrogen oxygen oxygen oxygen ½ hydrogen hydrogen hydrogen hydrogen

Joseph John Thomson in 1897: Discovered that atoms have negatively charged particles in them Concluded that since atoms are neutral they must also contain positive particles to balance the negatively charged particles Proposed that the atom is a lump of positively charged material with negative electrons all through it Atoms aren’t the smallest particles and do have distinct parts; a positive body and electrons Thomson’s atom positive material negative electrons your textbook’s version

How Thomson Found Negative Particles Production of Cathode Rays To Vacuum Pump Anode Green Glow Air at Very Low Pressure Cathode Discharge Tube He used a cathode ray tube like these ones The tubes contain small amounts of gas He used electricity to run a current through the gas in the tube The gas glowed The glow started from the negative end and went to the positive end Opposites attract so if the glow moved towards the positive end that meant it must have been negative That meant some kind of negative things from the atoms were moving We now call these particles electrons High voltage Generator

Production of Cathode Rays Green Glow Direction Production of Cathode Rays To Vacuum Pump Anode Green Glow Air at Very Low Pressure Cathode Discharge Tube High voltage Generator Green Glow Starts Here Green Glow Moves to Here Green Glow Direction

Ernest Rutherford’s 1907 study of atomic structure: He fired very tiny, fast, positive alpha particles at a very thin sheet of gold foil He expected the alpha particles to just pass straight through the spaces between the particles in the foil Some passed straight through, some veered off on angles, and some bounced back He concluded that atoms must have a positive core that the alpha particles were hitting He named this core the nucleus and proposed that the electrons revolved around the nucleus Atoms aren’t the smallest particles and do have distinct parts; a positive nucleus and electrons Rutherford’s atom positive nucleus revolving electrons

Rutherford’s Gold Foil Experiment Apparatus for experiment Path of alpha (α) particles

Neils Bohr in 1912: why don’t negative electrons collapse into the positive nucleus? He thought Rutherford’s model was fundamentally correct just not complete Something must be keeping the electrons from collapsing into the nucleus He determined that electrons only move in defined orbitals around the nucleus For electrons to move between orbitals they need specific amounts of energy He called these bundles of energy quanta Atoms have distinct parts; a positive nucleus and electrons that revolve around it in orbitals Bohr-Rutherford atom

Evolution of the Atomic Model to be continued … 1. Dalton’s atom 2. Thomson’s 3. Rutherford’s atom 4. Bohr-Rutherford atom Atomic Theorists on Teacher Tube videos http://streaming.teachertube.com/viewVideo.php?title=Atomic_Theorists&video_id=86254