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