1. Honors Chemistry Mrs. Coyle
Atomic Structure- Part I Early Atomic Theories From Democritus to Dalton
Honors Chemistry
Mrs. Coyle
Au image through STM

2. Democritus – Greek philosopher 4th Century BC
First to come up with the idea that matter is composed of tiny, indivisible particles called atoms(Greek “atomos”).
Leucipus also supported this idea.

3. Opposing Views Democritus’s ideas were opposed by Aristotle and Plato.
They considered matter to be continuous.
“The School of Athens” by Raphael

5. Proponents of the Idea of the Atom.
Robert Boyle and Isaac Newton (1600’s)

6. Antoine Lavoisier (France 1782)
Law of Conservation of Mass
In a chemical reaction mass is conserved.

7. Joseph Proust (France 1799)
Law of Definite Proportions:
A given compound always contains elements in a certain proportion by mass. (Constant composition).

8. Example:
KCl always contains potassium and chlorine in a ratio of “39.09 to 35.45” or “1.1 to 1” by mass.

9. John Dalton (England 1766-1844)- First Modern Atomic Theory
School teacher.
Studied the works of Proust and Lavoisier.
Formulated the first modern atomic theory.
In 1808, he published “A New System of Chemical Philosophy” stating his theory.

10. Law of Multiple Proportions (John Dalton)
When two elements combine to form more than one compound, the ratios of the mass of one element in the first compound to its mass in the second compound, (as it combines with the same mass of the other element), can always be expressed as ratios of small whole numbers( ex: 1 / 3).

11. Example of Law of Multiple Proportions
Carbon combines with oxygen to form CO and CO2 .
Mass of Carbon(g)
Mass of Oxygen(g)
Ratio of O in CO2 to O in CO CO
12.01
16.00
CO2
32.00
2/1

12. Dalton’s Atomic Theory
All matter is made of tiny particles called atoms.
Atoms of the same element are identical. Atoms of a given element are different from those of any other element.

13. Dalton’s Atomic Theory
Atoms of different elements can chemically combine in simple whole number ratios to form compounds.
Example: CO2

14. Dalton’s Atomic Theory
Chemical reactions occur when atoms are rearranged.
Chemical reactions do not change atoms of one element to another.

15. Dalton’s Atomic Model

16. Was Dalton completely right?
Much of Dalton’s theory still holds today.
However:
Atoms are not indivisible
Not all atoms of each element are the same, there are isotopes.

17. Progress is Made while Experimenting with Gases
Joseph Gay-Lussac (France 1809)
Performed experiments on gases, under the same temperature and pressure and measured their volumes.
He found that the volumes of the reacting gases and products were at small whole number ratios.
Ex: 2 L H2 and 1L O2 produce 2 L H2O(g)

18. Amadeo Avogadro’s Hypothesis (Italy 1811)
Equal volumes of different gases at the same conditions (T and P) contain equal number of particles.

19. The Size of the Atom
If you placed 100,000,000 Cu atoms side by side they would form a line only 1 cm long.
Radius of most atoms is about 5x10-11 to 2x10-10m.