1. Chapter 4 History of the atom
Last revised November 16, 2018
Use Interactive Chalkboard Disc 1 With Presentation

2. Greeks (400 B.C.)
Believed matter was made up of 4 fundamental substances:
Fire
Water
Earth
Air

3. Democritis ( B.C.)
A Greek who proposed the idea that matter is not infinitely divisible.
He coined the term atomos (atoms) to describe the smallest particles (ultimate particles)
Also, changes in matter result in changes in grouping of atoms
Aristotle rejected his ideas

4. Next ~200 years are all about Alchemy
Alchemists wanted to turn cheap metals into gold
Robert Boyle( )-”First Chemist” to perform quantitative experiments, measured the relationship between pressure and volume of gases

5. George Stahl (phlogiston) (1660-1734)
Antione Lavoisier( )
Explained nature of combustion
Verified Law of Conservation of Mass
George Stahl (phlogiston) ( )
Joseph Priestly ( ) Discovered Oxygen

6. John Dalton ( )
An Englishman who developed the Law of multiple proportions- when two elements that combine with 1g of the first element can always be reduced to small whole number.

7. Dalton’s Atomic Theory
Each Element is made up of tiny particles called atoms
The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways

8. Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms
Chemical reactions involve reorganization of the atoms-changes in the way they are found together. The atoms themselves are not changed in a chemical reaction

9. Dalton’s Other Ideas “Matter would be as simple as possible “
Prepared first table of atomic masses (weights) mostly wrong due to incorrect assumptions
His atomic theories are not all accurate

10. Atom-smallest particle of an element that retains all the properties
Gay-Lussac- Performed experiments in which he measured volume of gases that reacted with each other at same temperature and pressure

11. Avogadro- interpreted Gay-Lussac’s results and determined at the same temperature and pressure equal volumes of different gases contain the same number of particles (called Avogadro’s Hypothesis) Led to 22.4 L = 1 mol of gas and 6.022x 1023 molecules = 1 STP

12. William Crookes-developed the Cathode-Ray Tube

13. J.J. Thomson (1856-1940)-Discovered electrons using the cathode-ray tubes (pg 47)
did not name them electrons at the time
Determined the charges to mass ratio of the electrons
Also created the Plum pudding model of the atom

14. Milikan ( ) -Using the ratio determined by Thomson and his discovery of the negative charged electron, calculated the mass of the electron as 9.11x kg (Oil Drop Experiment)

15. Rutherford ( )-Determined most mass of atoms was located near the (+) charged center or nucleus around which electrons moved
(1911) Thin foil experiment
Also created a nuclear model

18. Mendeleev ( )-Credited with the development of the periodic table, originally arranged according to atomic weight, today according to atomic number

19. Bohr (1885-1962)-Electron Cloud Model or Planetary Model

20. The Quantum Mechanical Model is used as the current atomic model
There is no way to exactly know at any moment of time where an electron is exactly.

21. Most Famous Chemist of them all.