1. Bell-Ringer
How have your ideas about Santa Claus and the Easter Bunny changed as you have grown up?
Is it important to keep an open mind when it comes to new ideas in science?

2. Chapter 3: Atoms: The Building Blocks of Matter
Coach Kelsoe
Chemistry
Pages 66–88

3. Section 3-1 The Atom: From Philosophical Idea to Scientific Theory
Coach Kelsoe
Chemistry
Pages 66–71

4. The Atom
Around 400 B.C., Democritus gave the atom its name, based on the Greek word meaning indivisible.
“A” means not, and “tomos” means “cutting.”
Aristotle did not believe in atoms.
Democritus

5. Foundations of the Atomic Theory
In the 1790s, the law of conservation of mass was formulated.
The law of conservation of mass states that mass is neither created nor destroyed during ordinary chemical reactions or physical changes.
Created
Destroyed

6. Law Of Conservation of Mass
The number of carbon atoms and the number of oxygen atoms are the same before and after each reaction! + =
Carbon Oxygen CO
Mass x Mass y Mass x + y = +
CO Carbon Oxygen
Mass x + y Mass x Mass y

7. Foundations of the Atomic Theory
The law of definite proportions states that a chemical compound contains the same elements in exactly the same proportions by mass, regardless of the size of the sample or source of the compound.

8. Foundations of the Atomic Theory
The law of multiple proportions states that if two 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 first element is always a ratio of small whole numbers.
Carbon Monoxide
1 C: 1 gram
1 O: 1.33 grams
Carbon Dioxide
1 C: 1 gram
2 O: 2.66 grams

9. Dalton’s Atomic Theory
John Dalton’s theory explained the previous laws. His theory said:
All matter is composed of atoms.
Atoms of a given element are identical in size, mass, and other properties, and atoms of different elements differ in size, mass, and properties.
Atoms can not be subdivided, created, or destroyed.
Atoms of different elements combine in simple, whole-number ratios to form chemical compound.
In chemical reactions, atoms are combined, separated, or rearranged.

10. Modern Atomic Theory
Not all aspects of Dalton’s Atomic Theory are correct.
We know that atoms are divisible.
We know that elements can have atoms with different masses.
The important concepts are that all matter is composed of atoms, and that atoms of any one element differ in properties from atoms of another element.