1. The structure of the atom
Atomic theory
The structure of the atom

2. Early ideas of matter Greek philosophy
Believed matter was composed of 4 basic elements. (included warm, cold, wet and dry)
Earth
Air
Fire
Water

3. Modern atomic theories
Democritus ( B.C.)
Suggested all matter is made of small particles called atoms.
Start of atomic theory. (not well accepted)

4. Modern atomic theory Proust (1799)
Proposed the law of definite proportions.
Elements are always in the same proportion by mass in any sample of the same compound
Carbon dioxide is always the same % mass. 27% carbon 73% oxygen

5. Modern atomic theory Dalton (1766-1844) Dalton’s atomic theory.
All matter is atoms
Atoms cannot be divided.
All atoms of one element are alike, but they are different from atoms of any other element.

6. Modern atomic theory Conservation of mass
Atoms are never created or destroyed in normal processes, they just combine in different ways.

7. Atomic structure The electron
The negatively charged electron was discovered in a cathode-ray tube.

8. Atomic models Thompson’s model
Atoms are like scoops of chocolate chip ice cream
Electrons are scattered around the positively charged mass like chocolate chips in an ice cream scoop.

9. Atomic models What is the mass and charge of an electron?
Robert Millikan used an oil drop experiment to show the electron to be:
-1.6 x Coulombs
9.1 x grams

10. Atomic structure Protons
Anode rays produced positive charged streams that were deflected the opposite direction of cathode rays.

11. Atomic models Rutherford The gold foil experiment.
Showed the + charge had to be concentrated.

12. Atomic models What is the mass and charge of a proton?
Chadwick found the mass and charge were :
+ 1.6 x Coulombs
1.67 x grams
1 AMU

13. Atomic structure Neutron
Discovery of isotopes led to knowledge of neutrons.
HOW?

14. Atomic models Nuclear model
The protons and neutrons are found in the relatively dense nucleus and most of an atom is empty space.
The electrons are around the nucleus in different energy levels.

15. Atomic models What is the electron cloud model?
This is the current model.
More to come later

16. Atomic models How are atoms described?
Atomic number tells you the protons in an atom.
Mass number tells you protons + neutrons in an atom. (isotopes have different mass numbers)
Charge tells you the protons compared to the electron. (ions have charges)

17. Atomic models What happens when the nucleus is not stable?
When the nucleus changes, it is called radioactive decay.