2. The Four Quantum Numbers In the quantum mechanical model of the atom, each electron is described by four quantum numbers, and no two electrons in an atom can have the same numbers. The quantum numbers are: n: the principle quantum number. n = 1, 2, 3, 4… l: the angular quantum number. It describes the ‘shape’ of the orbital…the electronic distribution about the nucleus. l = n-1, n-2,… to 0 If l = 0, it’s an s orbital If l = 1, it’s a p orbital If l = 2, it’s a d orbital If l = 3, it’s an f orbital (and so on) m l : the magnetic quantum number. It describes the orientation of the orbital on an xyz-coordinate axis. m l = -l…0…+l in integral values. m s : the spin quantum number. It equals + ½ or - ½. Conventionally, the + ½ is always given first.

3. A few examples: 1 nlmlml 00 (all ms’s are ± ½, so won’t be shown here) Notes The 1s orbital 21 00 -1, 0, 1The three 2p orbitals. 2 The 2s orbital 32-2, -1, 0, +1, +2The five 3d orbitals. 31-1, 0, +1The three 3p orbitals. 3 00The 3s orbital

4. x y z x y z x y z pxpx pzpz pypy The three p-orbitals are oriented along the x, y and z axes and can hold a maximum of 2 electrons each. It’s been suggested that the p-orbitals look like peanuts if that helps you to remember their shape.

5. The d-orbitals d xy d xz d yz Even though the d-orbitals look like two p-orbitals, it is important to remember that each orbital can hold a maximum of 2 electrons regardless of how many lobes it has. d x 2 -y 2 dzdz 2

6. The freaky (or flowery) f-orbitals

7. And Electron Configurations Orbital Diagrams

8. H: 1 electron, 1s 1 Electron configuration Electrons behave as though they are spinning on their axis. A half arrow is used to indicate if the direction of the spin is up ( ) or down ( ).

9. He: 2 electrons, 1s 2 Pauli Exclusion Principle: Each orbital can contain 2 electrons ONLY if the electron spins are in opposite directions. Pauli Exclusion Principle: Each orbital can contain 2 electrons ONLY if the electron spins are in opposite directions.

10. Li: 3 electrons, 1s 2 2s 1 Auf bau principle: the electrons fill the orbitals starting with the lowest energy level and working their way up the energy ‘ladder’

11. Be: 4 electrons, 1s 2 2s 2

12. B: 5 electrons, 1s 2 2s 2 2p 1

13. C: 6 electrons, 1s 2 2s 2 2p 2 Hund’s Rule: all sublevel orbitals of the same energy must be filled with a single electron before the electrons can begin to pair up.

14. Sc: 21 electrons, 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 Total electrons 241012182021  complete configuration Shorthand notation:  noble gas core configuration 4s 2 3d 1 [Ar]

15. n 1 2 3 4 5 6 7 n -1 n -2 d-block metals f-block metals s-block metals p-block elements

16. 1s 1 1s 2 2s 1 2s 2 2p 1 2p 2 2p 3 2p 4 2p 5 2p 6 3s 1 3s 2 3p 1 3p 6 4s 1 4s 2 3d 1 3d 10 4p 1 4p 6 4d 1 4d 10 5d 1 We’ll look at the f-block tomorrow 4f 14 5f 14 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 8

17. Chemical reactivity depends upon the number of electrons in the highest energy level (the largest n). Electron dot structures show only the outermost electrons so that reactivity can be easily predicted. The outermost electrons are also called the valence electrons. Electron Dot Structures Rules to Drawing Electron Dot Structures 1.Electrons 1-4 are added singly. 2.Exception: If there only two electrons, they’re shown as a pair. 3.Electrons 5-8 are paired with the single electrons that are already there.

18. Xe Sr N Examples: 1. What is the electron configuration of strontium (Sr)? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 3p 6 5s 2 The highest energy level is n=5 and there are 2 electrons in it. Therefore, Sr has 2 valence electrons. 2. What is the electron configuration of nitrogen (N)? 1s 2 2s 2 2p 3 The highest energy level is n=2 and there are 5 electrons in it. Therefore, N has 5 valence electrons. 3. What is the electron configuration of xenon (Xe)? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 3p 6 5s 2 4d 10 5p 6 The highest energy level is n=5 and there are 8 electrons in it. Therefore, Xe has 8 valence electrons.

19. Excluding a few exceptions, how many valence electrons would all of the d-block and f-block elements have?

20. 1 234567 8 # Valence electrons

21. Electron Configuration Exceptions Hund’s Rule (part 2): For n ≥ 4, the energy of the electrons decreases (and stability increases) when all of the boxes for a sublevel are either half-filled OR completely filled. 4s 3d All of the orbitals are half-filled Cr 4s 3d Cu [Ar] All of the 3d orbitals are filled and the 4s orbital is half-filled

22. Where would the exceptions be in the 5 th through 7 th periods?