1. Atomic Structure
Ch. 4

2. Early Theories of Matter
Ancient Philosophers
Air, Earth, Fire, Water
Matter could be endlessly divided

3. Matter is composed of empty space through which atomos move
Democritus (460 – 370 B.C.)
Matter is made of tiny indivisible, indestructible, solid particles called atomos.
Matter is composed of empty space through which atomos move
Different kinds of atomos have different shapes and sizes
Ideas rejected
Largely by Aristotle

4. Dalton’s Atomic Theory
Matter is composed of extremely small particles called atoms
Atoms of a given element are identical
Atoms of a specific element are different from those of any other element
Different atoms combine in whole # ratios to form compounds
Chemical Rxn atoms are rearranged

5. An atom is the smallest particle of an element that retains the properties of that given element.

6. Subatomic Particles Relationship between matter and electric charge
How will electricity behave in the absence of matter
William Crookes
English Physicist
Noticed a flash of light
Cathode Ray

7. Cathode Ray Tubes

8. The negative particles in the ray are found in all matter.
By the late 1800s
Cathode Rays were actually a stream of charged particles
The particles carried a negative charge
The negative particles in the ray are found in all matter.
Called Electrons

9. J. J. Thomson Dalton Was Wrong!!!!
Determine the ratio of the charge to mass of the electron
Mass was much less than a Hydrogen atom
Dalton Was Wrong!!!!

10. 4.2: Continued Robert Milikan 1909 Mass of Electron
Determined the charge of the electron
1% of current value
Mass of Electron
9.1 x g
1/1840 mass of Hydrogen atom

11. Thomson’s Plum Pudding Model

12. Ernest Rutherford From New Zealand 1908 Nobel Prize for Chemistry
1911 studying alpha particles
Gold Foil Experiment

15. Rutherford concluded:
The plum pudding model was incorrect
There was a tiny dense, region centrally located in the atom that containing all the positive charge
The nucleus
Came up with a new atomic model

16. 1920
Rutherford concludes the nucleus of an atom contains positively charged particles called protons
James Chadwick
Coworker of Rutherford
Showed the nucleus contained a neutral subatomic particle called a neutron