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2. The Hydrogen Atom

3. Other Atoms Only 2 electrons fit in the lower shell. The 3rd electron must fit in the next shell.

4. Atomic Shells The discrete electron levels are arranged in shells. Each shell has a maximum occupancy. The first electronic shell can have at most 2 electrons, the second shell has room for 8 electrons and so on. The 1 st shell has the lowest energy. Thus, elements, in their lowest energy state fill the 1 st level first, and then fill the 2 nd level next. These elements are listed in the 1 st and 2 nd rows of the periodic table. Atoms are most stable if their outer shell is full. The electrons in outer shells are shielded by the inner shells from the full attraction of the nucleus. These electrons participate most readily in chemical reactions.

5. Atomic Shells How many electrons does neutral Carbon (6 protons) have in its outer shell? How many electrons does neutral Neon (10 protons) have in its outer shell?

6. The Periodic Table

7. Atomic Sizes

8. Ionization Energy

9. Periodic or Mendelev Table Tc: Li: solid, Cs: liquid, Ar: gas, Tc: synthetic # protons 1 e- in outer shell (Alkali Metals) Full outer shell (Noble Gases) 1 e- missing to fill shell (Halogens)

10. Bonding There are three major ways that elements bond to form molecules.

11. Ionic Bonds Atoms with filled shells, the Noble Gases, are highly inert. Atoms with one electron in the outer shell, and atoms with one electron missing are, on the other hand, highly reactive. These atoms form ionic bonds. The alkali gives up an electron. The halogen takes the electron. Elements are bonded by the electric force between the ions.

12. Example of ionic bonds Ruby Sapphire Aluminum oxide, Al 2 O 3

13. Metallic Bonds Atoms in a metals also give up electrons, however the electrons are not transferred to the other atom. Instead, they are shared by all atoms. The electron sea allows current to flow through metal. Metals thus make good conductors. In sodium, for example, 1 out of the 11 electrons is released so that Na has two filled shells. The extra electrons move around the metal in a “sea” of negative charge. This negatively charged sea moves around a regular structure of positive Na ions.

14. Covalent Bonds Certain molecules are formed by sharing electrons. The covalent bond that forms resembles metallic bonds in that electrons are shared. Yet, like ionic bonds the electrons are shared in discrete shells of the atoms and don’t run willy nilly throughout the material.

15. Question How would you covalently bond two oxygen atoms to make O 2 ? Oxygen has 8 protons & electrons. How many electrons would each O have to share with the other?

16. Periodic or Mendelev Table What kind of bonding does KBr have? # protons 1 e- in outer shell (Alkali Metals) Full outer shell (Noble Gases) 1 e- missing to fill shell (Halogens)

17. Answer

18. Question How would you expect KF to be bonded?

19. Periodic or Mendelev Table What kind of bonding does KBr have? # protons 1 e- in outer shell (Alkali Metals) Full outer shell (Noble Gases) 1 e- missing to fill shell (Halogens)

20. Answer Ionic Bond: K + F -

21. Multiple Covalent Bonds N2N2 78% O2O2 21% H2OH2O0-4% Ar0.9% CO 2 0.035% Ne0.0018% He0.0005% CH 4 0.0001% H2H2 0.00005% O3O3 0.000004% Earth’s Atmosphere Gases in Earth’s atmosphere are mainly covalently bonded molecules or noble gases. Combining C 6, N 7, O 8

22. Molecular attractions Polar molecules are more positively charged on one side and more negative on the other. This provides a cohesion.

23. Mars: why red?

24. Iron Oxides are present e.g. Hematite or Fe 2 O 3

25. Ozone Layer

26. Life on other planets

27. Summary Atoms have discrete energy levels, specific to that atom. A photon is absorbed when an electron jumps to a higher energy level. A photon is emitted when an electron drops to a lower energy level. The emitted/absorbed photon’s energy equals the difference between the atomic levels involved. Atomic levels can only fit a certain number of electrons (2 in the 1 st level, 8 in the 2 nd …) The periodic table is arranged according the electronic shells and the number of protons/electrons in the atom. Atoms with filled shells are most stable. Atoms bond in order to achieve this configuration. Ionic bonding involves the transfer of electrons from one atom to another. Covalent bonding involves the sharing of electrons by one or several atoms. Metallic bonding involves the sharing of electrons by the entire material/metal.

28. Radioactive Dating Parent ParentCarbon-14 Daughter DaughterNitrogen-14 Half Life Half Life 5,730 yrs* Potassium-40Argon-40 1.25 billion yrs Uranium-238Lead-206 4.5 billion yrs Thorium-232Lead-208 14 billion yrs Rubidium-87Strontium-87 48.8 billion yrs Samarium-147Neodymium-143 106 billion yrs Uranium-235Lead-207 704 billion yrs *Time that it takes wood to have half the C14 of a living plant.

29. Swisher et al. 1992, Science

30. Carbon Dating 1.Solar neutrons enter Earth’s atmosphere. 2.Neutrons collide with N 14 (7p, 7n), creating C 14 (6p,8n) [n + N 14  p + C 14 ] 3.Living bodies continually absorb C 14 (e.g. as CO 2 in photosynthesis). 4.When the plant or animal dies, it no longer assimilates C 14. 5.The C 14 decays (half life of 5730 yrs). [C 14  N 14 + e - + v e ] (n  p + e - + v e ) 6.The e - emission rate reveals the age. Measure ages < 70,000 yrs