The History of the The History of the Atomic TheoryAtomic Theory

DemocritusDemocritus

• 300 BC 

• Atom the indivisible; cannot be further broken down into smaller pieces".

• The atom as the smallest particle of matter.

Dalton Dalton c.1800 c.1800

- Atoms are seen as solid, indestructible - Atoms are seen as solid, indestructible spheres (like billiard balls) spheres (like billiard balls)

- Explains how atoms combine - Explains how atoms combine to form molecules.to form molecules.

- Confirms basic Laws of Chemistry: - Confirms basic Laws of Chemistry: “ “Conservation of Mass andConservation of Mass and Definite Proportions”.Definite Proportions”.

JJ ThomsonJJ Thomson

• C. 1850 

• Chocolate chip cookie model : Chocolate chip cookie model :

•   Atoms are solid spheres made-up of a Atoms are solid spheres made-up of a solid positive mass (or core) with tiny solid positive mass (or core) with tiny negative particles embedded in the negative particles embedded in the positive core.positive core.

RutherfordRutherford• 1905 • Famous Gold Leaf Experiment.Famous Gold Leaf Experiment.• Proved the atom is mostly made of empty Proved the atom is mostly made of empty

space.space.

• Proved that the nucleus is Proved that the nucleus is positive and the electrons are positive and the electrons are outside the nucleus.outside the nucleus.

BohrBohr• 1920 

• Electrons in definite energy levels Electrons in definite energy levels around  the nucleus.around  the nucleus.

• Proved that electrons are placed in Proved that electrons are placed in definite energy levels (called Orbitals) definite energy levels (called Orbitals) around the nucleus.around the nucleus.

• Speaks of Neutrons in the nucleusSpeaks of Neutrons in the nucleus

* 2, 8, 8, 2 ** 2, 8, 8, 2 *

Atomic Review Video

Main Principles:Main Principles:

- All matter is made up of tiny particles called - All matter is made up of tiny particles called atoms.atoms.

- Atoms are made of even smaller particles: Atoms are made of even smaller particles: Protons (+), Electrons (-), and Neutrons (o)Protons (+), Electrons (-), and Neutrons (o)

- Atoms can be distinguished from each Atoms can be distinguished from each other by their number of protons, electrons other by their number of protons, electrons and neutrons.and neutrons.

Periodic Table of ElementsPeriodic Table of Elements

What the heck does it mean?What the heck does it mean?

Each element is broken down the same way.Each element is broken down the same way.