1. Unit 2 – Electrons and Periodic Behavior Cartoon courtesy of NearingZero.net

4. Erwin Schrödinger (1926) Quantum mechanics – electrons can only exist in specified energy states Electron cloud model – orbital: region around the nucleus where e - are likely to be found

5. Erwin Schrödinger (1926) Electron Cloud Model (orbital) dots represent probability of finding an e - not actual electrons

6. Why Are Electrons location Important  Their arrangement around the nucleus determines an atom’s chemical ability

7. Quantum Numbers  Def: Where electrons are located in an atom  There are four quantum numbers, each describing a different aspect of the orbiting electron.

9. First Quantum Number The Principle Quantum Number  Describes the distance from the nucleus.  Referred to as energy levels. 3rd energy level 2nd energy level

15. Second Quantum Number aka sublevels  Describes the shape of the atom  There are four shapes, based on the movement of the electrons S P D F Too weird to show

17. Third Quantum Number  Orbitals  Describes the number of electrons each sublevel can hold

18.  s orbital can hold 2 electrons  Orbital: a space that can be occupied by 0, 1, or 2 electrons.  P orbital can hold 6 electrons  d orbital can hold 10 electrons  f orbital can hold 14 electrons

19. Fourth Quantum Number  Symbol =  describes the spin of the electron  They can either spin clockwise or counterclockwise.  No two electrons can have the same set of all four quantum numbers 1900 - 1958 electrons must spin in opposite directions! Ms

21. 322 6 10 14 13571357 spdfspdf 4 182 6 10 135135 spdspd 3 82626 1313 spsp 2 221s1 Number of electrons per main energy level (2n 2 ) Number of Electrons per sublevel Number of orbitals per sublevel Sublevels in main energy level (n sublevels) Energy Level (n) Energy Levels, Sublevels, Electrons

22. Feeling overwhelmed? Read Section 4-2!

27. Electron Configuration of Sodium For example, here is the ground- state configuration of sodium: Na 23 11 Sodium Atom 1s2 2s2 2p6 3s1

28. 2 types of electron notation 1. Long hand 2. Short hand

29. Purpose of electron notation Find valence electrons valence electron – electrons located in outer energy level

30. S 16e - Valence Electrons Core Electrons 1s 2 2s 2 2p 6 3s 2 3p 4 B. Notation Longhand Configuration

31. C. Periodic Patterns Period # – energy level A/B Group # – equals the total # of valence e - Column within sublevel block – # of e - in sublevel

32. Energy of Orbitals

33. s-block1st Period 1s 1 1st column of s-block C. Periodic Patterns Example - Hydrogen

34. Shorthand Configurations (1) Start with the last element on the previous row in brackets [ ]. (2) Find the difference in numbers of electron. (3) Add the remaining electrons by starting at the s orbital of the row that the element is in. Na = [Ne]3S 1

35. Fill in Shorthand Configurations 

36. 1 A neutral atom has electron configuration 1s22s22p63s23p2. What element is this? A carbon B nitrogen C silicon Dgermanium EI don't know how to answer this.

37. 2 A neutral atom has an electron configuration of 1s22s22p63s23p2. What is its atomic number? A 5 B 11 C 14 D 20 E I don't know how to answer this.

38. 3 A neutral atom has an electron configuration of 1s22s22p6. If a neutral atom holds one additional electron, what is the ground state configuration? A 1s22s22p63s1 B 1s22s22p7 C 1s22s32p6 D none of the given answers E I don't know how to answer this.

39. 4 What is the electron configuration for Li which has three electrons? A 1s3 B 1s12s2 C 1s22s1 D 1s21p1  E I don't know how to answer this.

40. Stability When the elements were studied it was notices that some of them do not react in certain situations in which others do. These elements were labeled "stable" because they did not change easily. When these stable elements were grouped together, it was noticed that periodically, there were patterns in the occurrence of stable elements. Today we recognize that this difference in stability is due to electron configurations.

41. Stability When the elements were studied it was notices that some of them do not react in certain situations in which others do. These elements were labeled "stable" because they did not change easily. When these stable elements were grouped together, it was noticed that periodically, there were patterns in the occurrence of stable elements. Today we recognize that this difference in stability is due to electron configurations.

42. 1 A 2A 8A 1 2 18 3 A 4A 5A 6A 7A 13 14 15 16 17 8B 3B 4B 5B 6B 7B 1B 2B 3 4 5 6 7 8 9 10 11 12 } Group Numbers There are two methods for labeling the groups, the older method shown in black on the top and the newer method shown in blue on the bottom.

43. 12345671234567 6767 Stability Elements of varying stability fall into one of 3 categories. The most stable atoms have completely full energy levels.

44. 12345671234567 6767 Stability Next in order of stability are elements with full sublevels.

45. 12345671234567 6767 Stability Finally, the elements with half full sublevels are also stable, but not as stable as elements with fully energy levels or sublevels.