1. Models of Atomic Structure

3. Dalton Model
Unbreakable neutrally charged spheres.

4. Thomson’s Cathode Ray Experiment
Cathode rays originate from neutrally charged atoms.
Cathode Ray Tube
Cathode rays have a negative charge and are deflected by electrical charges and magnetic fields.
Cathode rays are electrons.

5. Cathode Rays = Electrons

6. Cathode Rays = Electrons

7. Cathode Rays = Electrons

8. Plum Pudding Model
Negative electrons stuck inside and on the surface of a positive pudding.
Atom’s mass and positive charge is widely spread.
Electrons might wander but mostly motionless unless kicked out by a lot of energy.
Chocolate chips in ice cream.

9. Plum Pudding Model
Negative electrons stuck inside and on the surface of a positive pudding.
Atom’s mass and positive charge is widely spread.
Electrons might wander but mostly motionless unless kicked out by a lot of energy.
Chocolate chips in ice cream.

10. Rutherford’s Gold Foil Experiment – Predicted Results

11. Rutherford’s Gold Foil Experiment – Predicted Results

12. Rutherford’s Gold Foil Experiment – Actual Results

13. Actual Results

14. Rutherford’s Gold Foil Experiment
Most alpha particles (42He) passed right through the gold foil.
A few alpha particles had very large deflections.
The Plum Pudding model would predict only small deflections.
The mass and positive charge of an atom is concentrated in a very small nucleus.

15. Rutherford-Bohr Model
Nucleus takes up very little space.
Electrons jump up to a higher energy level when they absorb energy.
Electrons falls down to a lower energy level when they emit energy.
Electrons orbit in regular “planet-like” energy levels around the positive nucleus.

16. Rutherford-Bohr Model
Nucleus takes up very little space.
Electrons jump up to a higher energy level when they absorb energy.
Electrons fall down to a lower energy level when they emit energy.
Electrons orbit in regular “planet-like” energy levels around the positive nucleus.

17. Quantum Model Electron clouds not orbits.
Electrons are not found in fixed locations, but rather probabilities to be in a location.

18. s-orbitals

19. p-orbitals

20. Atomic Models Atomic Model Description Dalton
Solid, neutrally charged spheres.
Plum-Pudding
Negatively charged electrons in a glob of positive charge.
Like chocolate chips in vanilla ice cream.
Rutherford-Bohr
Negatively charged electrons orbit a positive nucleus. Like planets around the sun.
Quantum
Electrons are in layers of clouds around the nucleus.

21. Key Na 11 Atomic Number Number of Protons
Sodium
22.99
Atomic Number
Number of Protons
Number of Electrons (when atom is neutrally charged)
Property unique to each element

22. Key Na 11 Average atomic mass* Sodium 22.99
Weighted Average number of Protons and Neutrons (approximately)

23. Subatomic Particles the particles that make up an atom
Protons – high mass, positive charge. Found in nucleus.
Neutrons – high mass, no charge. Found in nucleus.
Electrons – low mass, negative charge. Found orbiting around nucleus. (abbreviated e– )

24. Basic Electrical Charge Laws
+ and – : Attract
(pull together)
– and – : Repel
(push away)
+ and + : Repel
Like charges repel and Opposites attract

25. An Atom
Nucleus
1 proton = H = hydrogen

26. Why doesn’t the electron fall into the nucleus?
It orbits because the electron is moving really fast around the nucleus.
Because the electron has such a low mass, even a small amount of energy makes it move very fast.

27. An Atom
Nucleus
1 proton = H = hydrogen

28. Another Atom
Size of atom
Size of nucleus
2 protons = He = helium

30. Cathode Rays = Electrons

31. He H B C N O Ne F Li Be P Al Si S Cl Ar Na Mg Br Kr K Ca I Xe

32. 4 e– in valence shell