1. Pauli Exclusion Principle  Austrian physicist Wolfgang Pauli stated his exclusion principle in 1925.  No two electrons in an atom can have the same set of four quantum numbers. (n, l, m l, m s )  Each orbital can only have only two electrons and they must have opposite spin.

2. Hund’s Rule  If a subshell contains more than one orbital (p, d, f), you must put one electron in each orbital before pairing them up.

3. Atomic Subshell Energies (Page 311)  Electrons are assigned to subshells in order of increasing n+ l values. If two subshells are equal, the smaller n is first.  Which would get electrons first? 4s or 4p? 5d or 6s? 4f or 5s?

4. Electron Configurations  We will write the electron configuration in three ways.  spdf notation is writing it using symbols.  Noble gas notation is a short version of spdf.  Box notation uses boxes and arrows to represent orbitals and electrons.

5. Example  Write the spdf, noble gas and box notations for sulfur.

6. Practice  Write the spdf, noble gas and box notations for bromine.  What element has the configuration 1s 2 2s 2 2p 6 3s 2 3p 5 ?

7. Assignment  Page 316 Exercise 7.3  Page 332 6, 12, 16

8. Electron Configurations of Ions  For positive ions, you have to take electrons away from its normal configuration.  Write configurations and determine which are paramagnetic.  Cu  Cu +  Cu 2+

9. Anions  For anions, you must add electrons.  O  O 2-

10. Practice  Write electron configurations for Fe, Fe 2+, Fe 3+, F and F -

11. Atomic Size  In general, atoms get bigger when moving down in a group and smaller when moving right in a period.  They get bigger down because you are moving to a new energy level each time you move down.  They get smaller to the right because the nucleus keeps gaining protons, and the positive charge draws the electrons in closer.  The exception to this is with transition metals. Once you get to the last few in each row, the repulsion from the electrons is greater than the pull of the protons and the atoms get bigger. This happens because the new electrons aren’t added to the valence shell.

12. Assignment  Page 321 Exercise 7.5  Page 333 18, 20, 23, 24, 25, 26

13. Questions  Which group of elements want to lose electrons most?  Which group of elements want to gain electrons most?  Would energy be gained or lost when removing an electron?  Would energy be gained or lost when adding an electron?

14. Ionization Energy  Ionization energy is the energy required to remove an electron from an atom.  When moving down, IE decreases. This is due to the fact that the valence electrons are further from the nucleus.  When moving right, IE increases. This is due to the increased charge of the nucleus.  Exceptions include going from s-block to p-block elements (p orbitals have higher energy) and moving to the second half of the p-block ( electrons must pair up).

15. Electron Affinity  Electron affinity is the energy change for a process where an atom gains an electron.  The energy will always be negative  Moving down a group will decrease the electron affinity (less negative). This is again because the electrons get further from the nucleus.  Moving right will increase the electron affinity (more negative). This is also because of the increase in charge.  Exceptions again include the first and fourth electrons in the p- block. Also, period 3 is greater than period 2(more room).

16. Practice  Compare the elements C, O, and Si.  Place them in order of increasing atomic radius.  Which has the largest ionization energy?  Which has the more negative electron affinity, O or C?

17. Assignment  Page 325 Exercise 7.6  Page 333 27-30

18. Ion Size  The trends are the same as for atomic radius.  Cations are smaller than the original atom.  Anions are larger than the original atom.

19. Isoelectric Ions  They have the same number of electrons  Why do the atoms keep getting smaller?

20. Chemical Properties  Elements in the same group have similar characteristics, alkali metals all react the same with water because they have one valence electron.  When the elements sodium and chlorine make a compound, they always form NaCl. Why don’t they form Na 2 Cl or NaCl 2 ?

21. Assignment  Page 330 Exercise 7.8  Page 333 32, 36, 38, 40, 44, 46, 52, 56, 64