Laws of Matter & Dalton’s Atomic Theory

Reviving the Ancient Idea

Review of Lavoisier

Defined what an element was. Proposed program for chemistry. Discovered conservation of mass.

What’s Next?

Quite clear that Aristotle was incorrect. But, what then was the world made up of? Elements? But, what then were elements made up

of?

Fortunately, advancements in instrumentation led to more precise balances and …

Other Laws Discovered

Law of Definite Proportions Law of Multiple Proportions In addition to the Gas Laws and

Conservation of Mass

Which law does this picture illustrate?

Gold element = 1.00 gGreen element = 0.80 g

Gold element = 1.00 gGreen element = 2.40 g

Gold element = 1.00 gGreen element = 1.60 g

Hydrogen gas (2.02g) + Oxygen gas 16.00g = Water 18.02

Which law does this picture illustrate?

Which law does this picture illustrate?

• Manufactured in a lab

50% oxygen by mass50% sulfur by mass

• Mined out of the ground

50% oxygen by mass50% sulfur by mass

Which law does this picture illustrate?

• Balloon at room temperature • Balloon heated up

The Atom becomes a theory

These developments led John Dalton to revive Democritus’ idea of the atom and create a theory of his own.

Dalton’s Atomic Theory

1. All matter is made of extremely small particles called atoms (in constant motion).

2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.

3. Atoms cannot be subdivided, created, or destroyed.

4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

5. In chemical reactions, atoms are combined, separated, or rearranged.

Conservation of mass

Point 3: Atoms cannot be subdivided, created, or destroyed.

Point 4: In chemical reactions, atoms are combined, separated, or rearranged.

Gas Laws

Point 1: All matter is made of extremely small particles called atoms (in constant motion).

Law of definite proportions

Point 2: Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.

Law of multiple proportions

Point 4: Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

Theory Accepted

Dalton’s theory was accepted because it explained what was seen.

But, it did not give a way to determine molecule formulas.How two atoms came together and in what

ratios to form compounds.Dalton knew water was a 1 to 8 ratio by mass

but thought the molecular formula was HO.

Matter

Pure SubstanceMixture

ElementCompoundHomogenous Heterogeneous

Ex. Air Ex. Granite Ex. Water Ex. Iron

Basic unit: Molecule Basic unit: Atom

Can it be separatedphysically?

NoYes

Yes YesNo NoUniform?

Chemicallyseparated?