1. Theories of the Atom

2. Ernest Rutherford (Gold Foil Experiment) Discovered that atoms have a positively charged central mass called the nucleus Hypothesis: – If positive and negative charges are uniformly distributed throughout atoms, then positively charged particles shot at a thin piece of gold foil should pass directly through Observations: – Most particles passed straight through – Some particles deflected at very large angles

3. Conclusion: -Positive particles deflect due to collisions with nucleus -The nucleus occupies a very small space even though it consists of most of the atom’s mass -The nucleus is surrounded by a cloud of negatively charged electrons -Most of the atom is empty space

4. Interpreting the Periodic Table

5. ATOMIC NUMBER The atomic number represents the number of protons in an atom’s nucleus 29 Cu copper 63.55 atomic number Hydrogen -Atomic number = 1 therefore H has one proton -Any atom that has a single proton in its nucleus can ONLY be hydrogen

6. ATOMIC MASS Since electrons have a relatively insignificant mass, the mass of an atom consists of the protons and neutrons Measured in atomic mass units (u) If the atomic mass (protons + neutrons) of lithium is about 7 and we know that Li has 3 protons (atomic number), how many neutrons does lithium have? 3 Li lithium 6.94 atomic mass

7. atomic number = # protons = total # of electrons atomic mass – atomic number = # of neutrons

8. H 1.01 1 He 4.00 2 345678910 1112131415161718 1920 LiBeBCNOFNe NaMg KCa AlSiPSClAr 6.949.0110.8112.0114.0116.0019.0020.18 22.9924.3126.9828.0930.9732.0735.4539.95 39.1040.08 1 21314151617 18

9. HYDROGEN (H) PROTONS: 1 NEUTRONS: 0

10. HELIUM (He) PROTONS: 2 NEUTRONS: 2

11. LITHIUM (Li) PROTONS: 3 NEUTRONS: 4

12. BERYLLIUM (Be) PROTONS: 4 NEUTRONS: 5

13. BORON (B) PROTONS: 5 NEUTRONS: 6

14. CARBON (C) PROTONS: 6 NEUTRONS: 6

15. NITROGEN (N) PROTONS: 7 NEUTRONS: 7

16. OXYGEN (O) PROTONS: 8 NEUTRONS: 8

17. FLUORINE (F) PROTONS: 9 NEUTRONS: 10

18. NEON (Ne) PROTONS: 10 NEUTRONS: 10

19. SODIUM (Na) PROTONS: 11 NEUTRONS: 12

20. MAGNESIUM (Mg) PROTONS: 12 NEUTRONS: 12

21. ALUMINUM (Al) PROTONS: 13 NEUTRONS: 14

22. SILICON (Si) PROTONS: 14 NEUTRONS: 14

23. PHOSPHORUS (P) PROTONS: 15 NEUTRONS: 16

24. SULFUR (S) PROTONS: 16 NEUTRONS: 16

25. CHLORINE (Cl) PROTONS: 17 NEUTRONS: 18

26. ARGON (Ar) PROTONS: 18 NEUTRONS: 22

27. POTASSIUM (K) PROTONS: 19 NEUTRONS: 20

28. CALCIUM (Ca) PROTONS: 20 NEUTRONS: 20