2 Definition of an AtomAn atom is the smallest particle into which an element can be divided and still be the same substance.
3 Democritus Proposes the Atom Can you keep cutting something in half forever?
4 Aristotle disagreesDemocritus’s ideas were largely ignored for centuries
5 John DaltonCreated an Atomic theory based on experiments.
6 Dalton’s Atomic Theory Atoms are small particles that cannot be created, divided, or destroyedAtoms of the same element are exactly alike.Atoms join with other atoms to make new substances.
7 J. J. ThomsonDiscovered that atoms can be divided into smaller particlesDiscovered one such particles called the electron.
8 Cathode-Ray tube Experiment When particles were passed through a magnet they were attracted to the positive end, causing the beam of particles to bend downward.Thompson inferred that there must two different sections of the atom, one positively charged and the other negative.He called the negative portion of the atom the electron.
9 The Thompson Model1. Electrons are embedded in a positively charged sphere, much like chocolate chips in cookie dough.
10 Ernest Rutherford Discovered the Nucleus of the Atom At the center of an atom is a small dense positively charged nucleus.The atom is mostly empty space through which electrons travel
12 The Gold Foil Experiment Shot a beam of particles at a thin piece of gold foil (so thin it was only 1 atom thick).Behind the foil was a piece of photographic filmMost of the particles passed right through the foil. But, occasionally one would be reflected right back at him, because it hit the hard dense nucleus.
13 Neils BohrSuggested that electrons travel around the nucleus in definite pathsStates that electrons can jump between energy levels