1. Octet Rule, Ion Formation, & Writing Lewis Dot Structures Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

2. The Octet Rule l Many elements have a tendency to gain or lose enough electrons to attain the same number of electrons as the noble gas closest to them in the periodic table. l Atom’s want to have a stable arrangement of e - ’s l They will lose, gain or share e - ’s to have 8 valence e -

3. Writing Lewis Dot Structures ELEMENTS l Determine how many valence electrons are in the atom. (This is what oxidation # is based on.) l Place the electrons around the element symbol as shown….

4. Mg Write the electron dot diagram for l Na l Mg lClC lOlO lFlF l Ne l He Na C O F He Ne

5. Bond Formation An ion will form bonds based on how many valence e - ’s (dots) it has: l Less than 4 dots, each dot is an available bonding site. l 4 or more dots, each missing dot is an available bonding site. K 1 bond 3 bonds P

6. DO WRITING LEWIS DOT STRUCTURES #1 & #2

7. IONS l Add one dot for every negative, subtract for each positive. l Designate the charge of the ion and place the entire structure in brackets. Draw the Lewis Structure for I -1. I Extra e -

8. DO WRITING LEWIS DOT STRUCTURES #3

9. Ionic Bonding NaCl transfer of electron + - NaCl

10. Ca +2 P -3 Ca +2 P lAlAll the electrons must be accounted for! Ionic Bonding Ca -3

11. Ionic Bonding Ca 3 P 2 Formula Unit Ca 2+ P 3- Ca 2+ P 3- Ca 2+ P 3- Ca 2+

12. DO WRITING LEWIS DOT STRUCTURES #5

13. How does H 2 form? ++ The nuclei repel But they are attracted to electrons They share the electrons

14. Hydrogen Bond Formation 0.74 A - 436 0 H – H distance Energy (KJ/mol) Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 318 no interaction increased attraction balanced attraction & repulsion increased repulsion Potential Energy Diagram - Attraction vs. Repulsion (internuclear distance)

15. Covalent bonds l Nonmetals hold onto their valence electrons. l They can’t give away electrons to bond. l Still want noble gas configuration. l Get it by sharing valence electrons with each other. l By sharing both atoms get to count the electrons toward noble gas configuration.

16. Covalent bonding FF lFlFluorine has seven valence electrons lAlA second F atom also has seven lBlBy sharing electrons lBlBoth end with full orbitals (stable octets) 8 Valence electrons

17. Single Covalent Bond l A sharing of two valence electrons. l Only nonmetals and Hydrogen. l Different from an ionic bond because they actually form molecules. l Two specific atoms are joined. l In an ionic solid you can’t tell which atom the electrons moved from or to.

18. How to show how they formed l It’s like a jigsaw puzzle. l I have to tell you what the final formula is. l You put the pieces together to end up with the right formula. l For example - show how water is formed with covalent bonds.

19. Water H O Each hydrogen has 1 valence electron Each hydrogen wants 1 more The oxygen has 6 valence electrons The oxygen wants 2 more They share to make each other happy

20. l Put the pieces together l The first hydrogen is happy l The oxygen still wants one more HO

21. Water l The second hydrogen attaches l Every atom has full energy levels l A pair of electrons is a single bond HO H H HO

22. Lewis Structures 1) Count up total number of valence electrons 2) Connect all atoms with single bonds - “multiple” atoms usually on outside - “single” atoms usually in center; C always in center, H always on outside. 3) Complete octets on exterior atoms (not H, though) 4) Check - valence electrons math with Step 1 - all atoms (except H) have an octet;if not, try multiple bonds - any extra electrons?Put on central atom

23. DO WRITING LEWIS DOT STRUCTURES #4 & 6

24. Multiple Bonds l Sometimes atoms share more than one pair of valence electrons. l A double bond is when atoms share two pair (4) of electrons. l A triple bond is when atoms share three pair (6) of electrons.

25. Carbon dioxide l CO 2 - Carbon is central atom ( I have to tell you) l Carbon has 4 valence electrons l Wants 4 more l Oxygen has 6 valence electrons l Wants 2 more OC

26. Carbon dioxide l Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short O C

27. Carbon dioxide l Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short O C O

28. l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond 8 valence electrons Carbon dioxide O CO

29. How to draw them l Add up all the valence electrons. l Count up the total number of electrons to make all atoms happy. l Subtract. l Divide by 2 l Tells you how many bonds - draw them. l Fill in the rest of the valence electrons to fill atoms up.

30. Examples l NH 3 l N - has 5 valence electrons wants 8 l H - has 1 valence electrons wants 2 l NH 3 has 5+3(1) = 8 l NH 3 wants 8+3(2) = 14 l (14-8)/2= 3 bonds l 4 atoms with 3 bonds N H

31. NHH H Examples l Draw in the bonds l All 8 electrons are accounted for l Everything is full

32. Examples l HCN C is central atom l N - has 5 valence electrons wants 8 l C - has 4 valence electrons wants 8 l H - has 1 valence electrons wants 2 l HCN has 5 + 4 + 1 = 10 l HCN wants 8 + 8 + 2 = 18 l (18 - 10) / 2= 4 bonds l 3 atoms with 4 bonds -will require multiple bonds - not to H

33. HCN l Put in single bonds l Need 2 more bonds l Must go between C and N NHC

34. HCN l Put in single bonds l Need 2 more bonds l Must go between C and N l Uses 8 electrons - 2 more to add NHC

35. HCN l Put in single bonds l Need 2 more bonds l Must go between C and N l Uses 8 electrons - 2 more to add l Must go on N to fill octet NHC

36. Another way of indicating bonds l Often use a line to indicate a bond l Called a structural formula l Each line is 2 valence electrons HHO = HHO

37. Structural Examples H CN C O H H l C has 8 electrons because each line is 2 electrons l Ditto for N l Ditto for C here l Ditto for O

38. Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide l CO OC

39. Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide l CO OC

40. Coordinate Covalent Bond l When one atom donates both electrons in a covalent bond. l Carbon monoxide l CO OC

41. How do we know if…? l Have to draw the diagram and see what happens. l Often happens with polyatomic ions and acids.

42. DO LEWIS DOT STRUCTURES AND MOLECULAR SHAPES #1