1. Writing Electron Configurations Noble gas method

2. Write an electron configuration for uranium (92 electrons).

3. 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 10 6p 6 7s 2 5f 4

4. Write an electron configuration for uranium (92 electrons). 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 10 6p 6 7s 2 5f 4 This can take a long time for large atoms, especially when the valence electrons are the only ones we care about.

5. Noble gas method This method represents a much quicker and easier way to identify valence electrons.

6. Noble gas method This method represents a much quicker and easier way to identify valence electrons. The s-sublevel is always the first sublevel to be filled within a particular energy level.

7. Noble gas method This method represents a much quicker and easier way to identify valence electrons. The s-sublevel is always the first sublevel to be filled within a particular energy level. The outermost energy level is the most important, so why not start there?

8. Noble gas method This method represents a much quicker and easier way to identify valence electrons. The s-sublevel is always the first sublevel to be filled within a particular energy level. The outermost energy level is the most important, so why not start there? 7s 2 5f 4 (start with the 7 th energy level)

9. Noble gas method This method represents a much quicker and easier way to identify valence electrons. The s-sublevel is always the first sublevel to be filled within a particular energy level. The outermost energy level is the most important, so why not start there? 7s 2 5f 4 (start with the 7 th energy level) [Rn] is used to represent the first 86 electrons.

10. [Rn] means the same thing as 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 10 6p 6

11. [Rn] means the same thing as 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 10 Therefore, [Rn]7s 2 5f 4 means the same thing as 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 10 6p 6 7s 2 5f 4

12. Write an electron configuration for selenium using the noble gas method.

13. Start with the s-sublevel for the period selenium is in (4s)

14. Write an electron configuration for selenium using the noble gas method. Start with the s-sublevel for the period selenium is in (4s) Select the noble gas from the previous period and place it in brackets ([Ar]4s)

15. Write an electron configuration for selenium using the noble gas method. Start with the s-sublevel for the period selenium is in (4s) Select the noble gas from the previous period and place it in brackets ([Ar]4s) The argon accounts for 18 of the 34 electrons needed. Continue until you reach 34.

16. Write an electron configuration for selenium using the noble gas method. Start with the s-sublevel for the period selenium is in (4s) Select the noble gas from the previous period and place it in brackets ([Ar]4s) The argon accounts for 18 of the 34 electrons needed. Continue until you reach 34. [Ar]4s 2 3d 10 4p 4

17. Electron configuration exceptions

18. Electrons are arranged in a way that maximizes stability.

19. Electron configuration exceptions Electrons are arranged in a way that maximizes stability. Sublevels that are filled are the most stable. Half-filled sublevels are stable. Anything else is unstable.

20. Chromium The noble gas configuration for chromium is expected to be [Ar]4s 2 3d 4

21. Chromium The noble gas configuration for chromium is expected to be [Ar]4s 2 3d 4

22. Chromium The noble gas configuration for chromium is expected to be [Ar]4s 2 3d 4 The 3d sublevel is unstable due to the single empty orbital.

23. Chromium The noble gas configuration for chromium is expected to be [Ar]4s 2 3d 4 Promoting one of the 4s electrons increases stability.