1. The Atom

2. The History of the Atom The Greek Model – 200 B.C.
Democritus – matter can be divided into smaller pieces until you get to the smallest possible piece.
Atomos - indivisible

3. The History of the Atom 1803 – John Dalton
All elements are composed of atoms.
Atoms are indivisible and indestructible.
Atoms of the same element are the same.
Atoms of different elements are different.
Compounds are formed by the joining of two or more elements

4. Dalton’s Model

5. The History of the Atom 1897 – J.J. Thomson “Plum Pudding” model
Atom was made up of a mixture of positive material with negative electrons scattered throughout.

6. “Plum Pudding” Model

7. The History of the Atom 1911 – Ernest Rutherford Gold Foil Experiment
“Shot” positively charged particles at a thin sheet of gold.
Some particles went straight through as if they hit nothing at all.
Conclusion: Atoms are made of mostly empty space. Most of the mass and the positive charges are in the nucleus and electrons travel around the nucleus.

8. The Gold Foil Experiment

9. The History of the Atom 1913 – Niels Bohr
Electrons move in definite orbits around the nucleus, much like planets around the sun.
These orbits or energy levels are located at certain distances from the nucleus

10. The Bohr Model

11. + - Parts of the Atom Type of Particle Charge Location Mass Proton
nucleus
1 AMU
Neutron
No charge
Electron -
orbits
0 AMU

12. Bohr Model Atomic Mass = # of Protons + # of Neutrons
Atomic Number = # of Protons
So,# of protons = Atomic number
# of Neutrons = Atomic Mass –Atomic Number
# of Electrons = # of Protons (for now at least)

13. The History of the Atom The Wave Model Based on Wave Mechanics.
Explains the complex movement of electrons in larger atoms.
Electrons move in a range of locations and it is impossible to predict there precise location.

14. The History of the Atom String Theory
The latest explanation of the structure of matter.
Says that the “fundamental” particles are tiny strings that vibrate much like the strings of a guitar. The frequency and energy with which they vibrate determine the type of particle they make up.
Since E=MC2, more energy means a more massive particle

15. Isotopes Atoms of the same element with different numbers of neutrons.
Carbon 12
6 protons
6 neutrons
Carbon 14
6 protons
8 neutrons

16. Ions Atoms that have lost or gained electrons
If an electron is lost, the ion will have a positive charge (subtract a negative, you get a positive)
If an electron is gained, the ion will have a negative charge.

17. Four Forces in the atom
Electromagnetic – attraction between positive protons and negative electrons.
Holds electrons in orbit.

18. Four Forces in the atom Strong Force - holds together the nucleus.
Protons repel each other, but if they get close enough, strong force holds them together.

19. Four Forces in the atom
Weak Force
-Responsible for radioactive decay.

20. Four Forces in the atom Gravity
Little role in the structure of the atom.
Weakest of the forces.