Models of Atomic Structure

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 • Electrons orbit in regular “planet-like” energy levels around the positive nucleus. • 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.

16. Rutherford-Bohr Model • Electrons orbit in regular “planet-like” energy levels around the positive nucleus. • 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.

17. Quantum Model • Electron cloudsnot 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

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

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

23. Subatomic Particlesthe 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 (push away) Like charges repel and Oppositesattract

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

32. 4 e– in valence shell