Atoms and Radioactivity

1. Atoms and Radioactivity slide 1: Show Day After video (begin at first nuclear explosion and stop at little girl saying, “what’s radioactivity?” slide 6: Rutherford of Nelson video from start to his marks at Nelson college slide 6: Applet set up enlarged on other computer

2. Overview • Early models of the atom • Radioactive decay • Solving half life problems • Writing balanced nuclear equations • Understanding of the alpha, beta and gamma decay

3. John Dalton Early 1800s • John Dalton, an observer of weather and discoverer of color blindness among other things, came up with atomic theory • All matter is made up of small indivisble particles known as “atoms”

4. J.J. Thomson (1856 -1940) • Studied the “mysterious cathoderays” • In 1903 he proposed that… • the atom is a sphere of positive charged matter with electrons embedded like the currents in a “plum pudding” View Model

6. Ernest Rutherford • Famous for his gold foil experiment • Atom is mainly empty space • Small dense positively charged nucleus • Electrons orbiting the nucleus

7. Atomic Model after Rutherford

8. John Dalton’s model of the atom includes: A) B) C) D) F) E) electrons protons neutrons all the above none of the above other

9. Ernest Rutherford’s model of the atom includes: A) B) C) D) F) E) electrons protons neutrons all the above none of the above other

10. J.J. Thomson’s model of the atom includes: A) B) C) D) F) E) electrons protons neutrons all the above none of the above other

11. An alpha particle is: B) C) D) negatively charged positively charged not charged

12. Developing Rutherfords Model Observation Describe the path of the alpha particles in the gold foil experiment: • Most passed right through the gold foil • Some were deflected • A rare few bounced directly backwards

13. Developing Rutherfords Model Explanation Describe the atomic structure indicated by the observation. • It is mostly empty space • It contains a positive charge in its centre or nucleus that repels/deflects alpha particles • The positive charge must be densely packed to make alpha particles rebound backwards once in a while

14. Overview • Early models of the atom • Radioactive decay • Solving half life problems • Writing balanced nuclear equations • Understanding of the alpha, beta and gamma decay

15. Some Questions About:Atomic NumberMass Number andIsotopes

16. Atomic number is the number of ______in the atom protons neutrons electrons protons and neutrons A) B) C) D)

17. Mass number is the number of ______in the atom protons neutrons electrons protons and neutrons B) C) D) E)

18. To distinguish between isotopes of an element one needs to know the number of ______ in each. protons neutrons electrons protons and neutrons B) C) D) E)

20. The story continues… With the help of quantum theory that was being developed by Planck, Einstein and others the model continued to evolve… • Neils Bohr (1913): electrons occupy fixed energy levels (not fixed positions) • Louis de Broglie (1924): electrons are waves • Erwin Scrodinger (1925): electrons are matter waves whose position is based on a statistical probability (enter quantum mechanics)