Chapter 3.1

Objectives 1. Explain the law of mass, the law of definite proportions, and the law of multiple proportions 2. Summarize the five essential points of Dalton’s theory 3. Explain the relationship between Dalton’s atomic theory and the three laws

Atom: Philosophy to Scientific Theory.  Democritus – Greek philosopher ( 400 BC)  Called nature’s basic particle an atom, meaning indivisible  Aristotle – succeeded Democritus  Did not believe in atoms – thought all matter was continuous  His views had a lasting impact on Western Civilization  Accepted nearly 2000 years  There was no experimental evidence until the eighteenth century of the existence of the atom.

Foundations of Atomic Theory  Law of conservation of mass  States that mass is neither destroyed nor created during ordinary chemical reactions.  If you start with 12 g of reactant, you will be left with 12 grams of product Visual Concept 1 – Click Here Visual Concept 2 – Click Here

 Law definite proportions  State that a chemical compound contains the same proportions by mass regardless of the size of the sample or source of the compound  Sodium Chloride – always % by mass Na and 60.66% Cl by mass  Law of multiple Proportions  If 2 or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the element is always a ratio of small whole numbers  Ex: NO 2, N 2 O 4  CO, CO 2 Visual Concept – Click Here

Examples: Law of Conservation of mass and Law of definite proportions

Example: Law of multiple proportions

Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms 2. Atoms of a given element are identical 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. In 1808, and English School teacher, John Dalton came up with these assumptions of the atom.

Modern Atomic Theory  Modifications to Dalton’s Theory  Atoms are divisible into smaller particles  A given element can have atoms with different masses