1. Chapter 2: Modern Atomic Theory Matter consists of atoms Atoms consist of three fundamental particles, found in the nucleus and the space around the nucleus

2. Arrangement of Subatomic Particles not to scale! If an atom has a diameter of about 100 m (a football field), the nucleus would be 1 mm in diameter Nucleus contains protons and neutrons.

3. What holds an atom together?

4. Coulomb’s Law of electrostatic interactions.

5. What holds an atom together? Coulomb’s Law of electrostatic interactions. General Behavior: Like charges repel. Opposite charges attract.

6. What holds an atom together? Coulomb’s Law of electrostatic interactions. If we double a charge from +1 to +2, the force will: 1.Double 2.Halve 3.Quadruple 4.Quarter

7. What holds an atom together? Coulomb’s Law of electrostatic interactions. If we double the distance, the force will: 1.Double 2.Halve 3.Quadruple 4.Quarter

8. What’s wrong with this picture? Electrons are held near the nucleus by the electrostatic attraction between them, but … The forces of nature:

9. How could we possibly know that the nucleus is small compared to the size of the atom? Why not think the protons, electrons and neutrons are all mixed together? The Rutherford Experiment We’re not just making it up!

10. The Rutherford Experiment We’re not just making it up!

11. The Rutherford Experiment We’re not just making it up!

12. Atom Terminology All atoms of an element have the same atomic number = number of protons In a neutral atom (no charge), the number of positively and negatively charged particles must be equal. Number protons = number electrons The mass number = protons + neutrons

13. Isotopes Isotopes are atoms of an element with the same number of protons but different numbers of neutrons, and different mass Atom symbols are written using the following format: X = symbol of element A = mass number Z = atomic number

14. Isotopes, continued Most elements have multiple isotopes – 1 H, 2 H (deuterium), 3 H (tritium, radioactive) – 79 Br, 81 Br – 64 Zn, 66 Zn, 67 Zn, 68 Zn, 70 Zn While atomic mass is the mass of an atom, average atomic mass takes into account isotopes and natural abundance We use atomic mass units (amu) 1 amu = 1.661 x 10 –24 g (about the mass of a proton)

15. WHAT TIME IS IT? Puppy Dog Isotopes

16. Chiuaua: 4 lbs. Mastif: 120 lbs. What is the average weight of a collection of these dogs?

18. 96 % Chiuauas @ 4 lbs. 4 % Mastifs @ 120 lbs.

19. Isotopes and Average Atomic Masses

20. B has 2 isotopes: B-10: mass = 10.0129 amu abundance = 19.91% B-11: mass = 11.0093 abundance = 80.09% Example: Boron What is the average atomic mass of Boron?

21. What time is it?

22. HOW

23. HOW DO

24. HOW DO YOU

25. HOW DO YOU KNOW

26. HOW DO YOU KNOW THAT?

27. Mass Spectrometry

28. Isotopes In The News http://www.nytimes.com/2007/08/21/science/21mari.html?ex=1188705600&en=7d1e0dc4064c4cfe&ei=5070 http://www.nytimes.com/2007/04/24/sports/othersports/24landis.html?ex=1188705600&en=1241fcb09b9c265c&ei=5070