Atomic TheoryGrade 9 Science

Theories and Laws

What’s the difference between a theory and a law??

LawsDescriptions of events or patterns that have been observed over long periods of time

Do not involve an explanation, simply state what happens

Theories

Explain observations that are supported by experimental evidence

Can change if new evidence becomes available

Development of the Atomic Theory

Men and women from different countries have contributed to our understanding of the atom

Early Greeks contributed to the Atomic Theory

Empedocles: http://en.wikipedia.org/wiki/Empedocles

Democritus:http://www.timelineindex.com/content/view/1228

Aristotle: http://cstl-csm.semo.edu/mcgowan/ch181/atomhist.htm

John Dalton1766 - 1844

Dalton Atomic Theory

State the 4 points of Daltons Atomic Theory:1

2

3

4

JJ Thomson1856 - 1940

Atoms composed of small particles

Atoms contain negatively charged particles called electrons

Raisin bun model

Ernest Rutherford1871 - 1937

Conducted “Gold Foil Experiment”

Realized large space within atoms

Discovered the nucleus of the atom

Established that the nucleus had 2 types of particles: proton (+) and neutron (0)

Gold Foil Experiment

Positive particles

Neils Bohr1885 - 1962

Studied the area around the nucleus

Area around nucleus contained electrons (-)

Ran electric current through gas and observed the gas glowing brightly

Proposed electrons surround nucleus in specific energy levels

Bohr’s Model Glowing Neon Gas

Study the structure of the Atom with its three sub-atomic particles