1. Atoms, Molecules, and Ions

2. History Greeks Democritus and Leucippus - atomos Aristotle- elements.
Robert Boyle- experimental definition of element.
Lavoisier- Father of modern chemistry.

3. Laws Conservation of Mass
Law of Definite Proportion- compounds have a constant composition.
The react in specific ratios by mass.
Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers.

4. Dalton’s Atomic Theory
Elements are made up of atoms
Atoms of each element are identical. Atoms of different elements are different.
Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom.
Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.

5. Experiments to determine what an atom was
J. J. Thomson- used Cathode ray tubes

6. Thomson’s Experiment
Voltage source - +

7. Thomson’s Experiment
Voltage source - +

8. - + Thomson’s Experiment Voltage source
Passing an electric current makes a beam appear to move from the negative to the positive end.

9. Thomson’s Experiment
Voltage source
By adding an electric field

10. Thomson’s Experiment Voltage source + -
By adding an electric field, he found that the moving pieces were negative

11. Thomsom’s Model Found the electron.
Couldn’t find positive (for a while).
Said the atom was like plum pudding.
A bunch of positive stuff, with the electrons able to be removed.

12. Millikan’s Experiment
Atomizer
Oil droplets - +
Oil
Telescope

13. Millikan’s Experiment
X-rays
X-rays give some electrons a charge.

14. Millikan’s Experiment
From the mass of the drop and the charge on
the plates, he calculated the mass of an electron
Some drops would hover

15. Radioactivity Discovered by accident Bequerel Three types
alpha- helium nucleus (+2 charge, large mass)
beta- high speed electron
gamma- high energy light

16. Rutherford’s Experiment
Used uranium to produce alpha particles.
Aimed alpha particles at gold foil by drilling hole in lead block.
Since the mass is evenly distributed in gold atoms alpha particles should go straight through.
Used gold foil because it could be made atoms thin.

17. Florescent
Screen
Lead block
Uranium
Gold Foil

18. What he expected

19. Because

20. Because, he thought the mass was evenly distributed in the atom.

21. What he got

22. How he explained it
Atom is mostly empty
Small dense, positive piece at center.
Alpha particles are deflected by it if they get close enough. +

23. +

24. Modern View The atom is mostly empty space. Two regions
Nucleus- protons and neutrons.
Electron cloud- region where you might find an electron.

25. Formulas for acids hydrofluoric acid dichromic acid carbonic acid
hydrophosphoric acid
hypofluorous acid
perchloric acid
phosphorous acid