1. Part 1 – The concept of the Atom
The History of the Atom
Part 1 – The concept of the Atom

2. A long time ago, in a galaxy country far, far away
There were two philosophers

3. One was Democritus Lived in Ancient Greece
First to use the term atom (atomos meaning indivisible)
Described the atom by mathematics of the day (His peer was Pythagoras)
Atom was described as the smallest part of a material
1st person to propose that matter was not infinitely divisible
Thought that atoms could not be created, destroyed, or further divided
There were rock atoms, hair atoms, etc.

4. Democritus’s atom would have looked like this:
Solid and Indestructible
No electrons
No nucleus
No protons
No neutrons
No Experiments to support his ideas

5. The other was Aristotle
He lived in the heart of Greece (Athens)
Very influential
Opposed because he didn’t think empty space exsisted
Defined matter as composed of hot, cold, wet and dry
These properties related to fire, air, water, and earth
Everything differed by the percentages of each that composed the object

6. And the winner was: Aristotle And set chemistry back about 2000 years
Chemistry didn’t make a come back until the Renaissance

7. John Dalton
Took his own experiments and those of others to write a paper, which later became known as the Modern Atomic Theory
Similar to Democritus’ ideas
It gave a compilation of the information at the time and allowed other scientist to test his ideas.

8. Dalton's Atomic Theory
Matter is composed of extremely small particles called atoms
Atoms are indivisible and indestructible
Atoms of a given element are identical in size, mass & chemical properties
Atoms of a specific element are different from those of another atom
Different atoms combine in simple whole number ratios to form compounds
In a chemical reaction, atoms are separated, combined or rearranged

9. An Analogy for Dalton’s atom
An atom is small, spherical and the same throughout.
A small atomic fireball

10. Dalton also gave us the Law of Multiple Proportions
Elements could combine in different ratios to produce different compounds
For Example, nitrogen and oxygen can form N2O, NO, NO2, N2O3, N2O4, and N2O5.

11. His ideas weren’t 100% correct, but they gave scientist a good start

12. Definite and Multiple Proportions – The Math Involved
Types of problems that can be asked at this point in time.

13. Type One – The Easy Type
Table salt is composed of sodium and chlorine. Chlorine comprises 60.66% of the compound, what percentage is sodium?
39.34%
C, H, and O combine to make C2H6O2. Hydrogen is 9.74% and carbon is 38.70%. What percent is oxygen?
51.56%

14. Type 2 – You will need a periodic table for this type
The formula of ethylene glycol is C2H6O2, what percentage by weight do you have of each of the elements?
Step 1 – Calculate the mass of C2H6O2, by adding the mass of each element:
C = g x 2
H = 1.01 g x 6
O = g x 2
= g
= g
= g
62.08 g

15. Type 2 – You will need a periodic table for this type
Step 2 – Divide each elemental mass by the mass of the compound
C = g x 2
H = 1.01 g x 6
O = g x 2
Step 3 – Multiply by 100
C = 38.69%; H = 9.76%; O = 51.55% 
= g
62.08 g =
= g 
62.08 g =
= g 
62.08 g =
62.08 g

16. Let’s try this one together
What percentage by weight do you have of each of the elements if you have the formula Al2O3?

17. Now try the rest of the problems with you groups

18. Answers 42.9% C and 57.1% O 77.7% Fe and 22.3% O 2.7% H and 97.3% Cl
52.2% C, 13.0 % H, and 34.8% O
32.4% Na, 22.6% S, and 45.0% O