John Dalton•Elements Composed of indivisible atoms.•Atoms are alike for a given element.•Atoms for different elements differ in size, mass, etc.•Compounds are formed from two or more atoms of different elements.•Atoms combine is simple numerical ratios to form compounds.

Dalton’s Atomic Theory

Rule of Greatest SimplicityWhen atoms combine in only one ratio, "..it must be presumed to be a binary one,unless some cause appear to the contrary"

Law of Combining Volumes

Joseph Louis Gay-Lussac (1778 - 1850)

The ratio between the volumes of the reactant gases and the products can be expressed in simple whole numbers.

Synthesizing Water Vapor

Synthesizing Ammonia Gas

Synthesizing Carbon Dioxide

Equal Volumes of Gas Contain Equal Numbers of “Particles”

Problems Interpreting Combining Volume Data

Assume Water’s Chemical Formula is HO

Assume Water’s Chemical Formula is H2O

The Answer!Amedeo Avogadro (1776 - 1856)

Stanislao Cannizzario (1826 - 1910)

H2 O2 H2O

Meyer’s Reaction to Cannizzaro

It was as though the scales had been lifted from my eyes.

Doubt vanished and was replaced by a feeling of peaceful clarity.

Julius Lolthar von Meyer (1830 – 1895)

Oxides of Carbon?

Berzelius’ Table of Atomic Weights (1814)Element Based on O

=100Based on O = 16

Modern, Based on C-12 = 12

Hydrogen 6.636 1.062 1.00794

Boron 73.273 11.724 10.811

Carbon 75.1 12.0 12.0107

Nitrogen 79.54 12.72 14.0067

Oxygen 100 16 15.9994

Fluorine 60.0 9.60 18.998403

Phosphorus 167.512 26.8019 30.973761

Sulfur 201.00 32.160 32.065