1. History of the Atom
SWBAT #1: Describe the development of the model of the atom through history
SWBAT #2: Identify the main components of the nuclear atom

2. History of Atom Video

3. Democritus – 400BC Greek philosopher
Was first to suggest the existence of atoms
Believed all matter was made up of atoms and that atoms were indivisible and indestructible
Atoms are indivisible and indestructible
No internal Structure

4. Dalton’s Atomic Theory
Using experimental methods Dalton ( ) developed an atomic theory
All elements are composed of tiny indivisible particles called atoms
Atoms of the same element are identical AND atoms of any one element are different from those of other elements
Atoms of different elements can physically mix together to form mixtures or can chemically combine to form compounds
Chemical reactions occur when atoms are separated, joined, or rearranged

5. Dalton’s Atomic Model - 1803
No internal structure

6. What’s in an Atom
Throughout history several scientists have performed experiments to figure out what exactly makes up atoms
The two we will be studying are Thomson’s Cathode Ray experiment and Rutherford’s Gold Foil experiment

7. Thomson Model -1897 Cathode Ray Experiment Discovered electrons
Internal Structure
Ball of positive charge containing electrons
Often referred as the plum pudding model

8. Cathode Ray
At both ends of the sealed tube are metal discs which are connected to electricity
In the tube is gas
Pass electric current through the gas
The cathode ray that showed up when the power was turned on was attracted to a positive plate

9. Wait….. Let’s think about this
If Thomson discovered that atoms have negative particles called electrons……
AND atoms are electrically neutral
What else might they have in the same number of electrons?
Another scientist named Golstein observed rays traveling in opposite direction of the cathode rays. He called them canal rays. We call them protons!
Atoms have protons. Positive charged particles in the same number as electrons.

10. Rutherford Model
1. Gold Foil Experiment 2. Discovered the nucleus 3. Concluded that an atom is mostly empty space with the nucleus in the center. AND The nucleus contains almost all the mass of the atom with protons and neutrons inside.

11. Gold Foil Experiment
Due to Thomson scientists believed atoms are just balls of positive and negative particles
If you shoot radiation at the atom it should pass strait through.
Rutherford sent alpha radiation at gold foil expecting the radiation to pass through
Most of it did…….. Some of the radiation bounced back!!! What was the radiation hitting?

12. Gold Foil Experiment

13. Rutherford Model - 1911 Internal Structure
Nucleus contains protons and neutrons
Electrons float around the nucleus

14. Comparison
Thomson
Rutherford

15. The Nuclear Atom Has…. Atoms have a tiny nucleus
The nucleus contains most of the mass of the atom
Protons and neutrons are found in the nucleus
Electrons are outside the nucleus
Particle
Symbol
Charge
Mass
Electron e- 1-
1/1840 amu
Proton p+ 1+
1 amu
Neutron n0

16. Something to Think About
If the atom was the size of a football stadium
How big would the nucleus be?
The size of a marble (with all the mass of the stadium in it)

17. Bohr Model - 1913 Internal Structure
Nucleus contains protons and neutrons
Electrons travel in fixed circular orbits around the nucleus

18. Comparison
Rutherford
Bohr

19. Quantum Mechanical Model - 1926
Internal Structure
Nucleus contains protons and neutrons
Physicists decide that the atom has no definite shape and electrons don’t have precise orbits
Instead electrons are found in regions called atomic orbitals
Electron Cloud
Draw a circle around the
atomic orbitals, high
probability of finding
all electrons

20. Comparison
Bohr
Quantum Mechanical Model

21. Dalton to Quantum Mechanical Model – The history of the model of the Atom