Notes: Atomic TheoriesCW: Models of the AtomH: Extra! Headline News
Atomic Theories
December 5, 2008
Objectives
1. Describe the relationship between theories and models.
2. Summarize how atomic theories have changed.
3. Define atom and its parts
Why use models?
• Simplify the idea
• Allow us to visualize
• Help us predict
• Before 400 BC, Greeks defined atoms as smallest part of matter
• Before scanning electron microscope (1981), no one had seen at atom
Democritus 440 BC
Said you would end up with an un-cutable piece of matter
• “Atom” from Greek atomos (indivisible)
• No evidence
John Dalton 1800’s
Billiard ball model” based on experimental evidence
• All matter is made of atoms.• Atoms of each element are
alike.• Atoms can not be created,
destroyed or changed.• Atoms can join to form new
substances.
JJ Thomson 1897
“Plum pudding model”
• Atoms contain subatomic particles
• Atoms have negative particles (electrons)
• Electrons stuck in a positive sphere
Ernest Rutherford 1909
Peach model
• Dense, positive region (nucleus)
• Electrons fly around nucleus
Niels Bohr 1913
Planetary model
• Electrons exist in energy levels
• Electrons contain certain energy
Schrodinger & Heisenberg 1928
Electron cloud model, “Spinning fan”
• Electrons move in a region around nucleus
• Orbitals - regions of most probable electron location
Schrodinger & Heisenberg
Electron cloud model
Scientist Theory
Democritus
Dalton
Thomson
Rutherford
Bohr
Heisenberg & Schrodinger
Matter is made of indivisible atoms
Atoms are unchangeable, but can join
Electrons have negative charge
Positively charged nucleus
Electrons exist in energy levels
Position of electrons is uncertain
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