1 Chapter 8 Covalent bonding

2 I. Octet Rule l What is the Octet Rule? l The octet rule states that atoms lose gain or share electrons in to acquire a full set of 8 valence electrons Create a drawing of Mg and Cl, Al and Cl

3 II. Covalent Bonds A Chemical Bond occurs when electron are shared. Hydrogen and Hydrogen A molecules are formed from the overlap of orbitals and sharing of electrons

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

5 Its all in the distance a. Too far no bond b. Too close electrons repel c. Just right and a molecule is born A molecules are formed from the overlap of orbitals and sharing of electrons

6 Covalent clip

7 III. Molecule l A. a covalently bonded compound. –1. Tend to occur between non metals that are close together on the periodic table. – a. diatomic molecules – occur naturally in nature a. this is a more stable arrangement. H H F F Br Br Cl Cl N N

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9 I. Single Covalent Bond A. A sharing of two valence electrons. 1.Only nonmetals and Hydrogen. 2.Different from an ionic bond because they actually form molecules. 3. Two specific atoms are joined.

10 How does H 2 form? l The nuclei repel ++

11 When Atoms Combine to make Molecules Fig 8-1 Atoms contain both positive and negative charges. When they come Together they arrange themselves so that the attractive forges of opposite Charges is greater than the repulsive forces of like charges

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

13 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.

14 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

15 Water l Put the pieces together l The first hydrogen is happy l The oxygen still wants one more H O

16 Water l The second hydrogen attaches l Every atom has full energy levels H O H

17 l use acetate sheets to work on page to create lewis structures l Use a square of acetate to show each atom (use vis a vis pens only) l Show the overlap of orbitals l Draw the outcome in your notebook-use structural formula (line to represent pair) l Circle the shared pairs

18 Lewis structure l 1. PH 3 l 2. H 2 S l 3. HCl l 4. CCl 4 l 5. SiH 4

19 Lewis structure l Use molecular model kit to build l 1. PH 3 l 2. H 2 S l 3. HCl l 4. CCl 4

20 Covalent Bond Formation l Covalent bond forms by overlap of orbitals. l Two types of bonds  Sigma bond: all single bonds are sigma bonds  Pi bond: in multiple bonds: the first one is sigma, all other bonds are pi. There are  Single bonds  Multiple bonds (double and triple only)

21 Two types of Bonds l Sigma bonds from overlap of orbitals along the axis connecting the nuclei between the atoms Pi bond (  bond): perpendicular overlap of p-orbitals above and below the axis connecting the atoms

22 Sigma bond: s-s Orbital Overlap

23 l Pg 247- # 12 a-e

24 III. Multiple Bonds A. Sometimes atoms share more than one pair of valence electrons. B. A double bond is when atoms share two pair (4) of electrons. C. 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 O C

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 Carbon dioxide l The only solution is to share more O C O

29 Carbon dioxide l The only solution is to share more O C O

30 Carbon dioxide l The only solution is to share more O CO

31 Carbon dioxide l The only solution is to share more O CO

32 Carbon dioxide l The only solution is to share more O CO

33 Carbon dioxide l The only solution is to share more O CO

34 Carbon dioxide 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 O CO

35 Carbon dioxide 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 O CO 8 valence electrons

36 Carbon dioxide 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 O CO 8 valence electrons

37 Carbon dioxide 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 O CO 8 valence electrons

38 How to draw them l Add up all the valence electrons. l Count up the total number of electrons to make all atoms complete octet rule. 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.

39 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

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

41 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 = 10 l HCN wants = 18 l (18-10)/2= 4 bonds l 3 atoms with 4 bonds -will require multiple bonds - not to H

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

43 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

44 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

45 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

46 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

47 l Build the molecules using the molecular model kit. l HCN l H 2 O l NH 3 l CH 4 l C 2 H 2 l PH 3 l H 2 S l 5uslaNo 5uslaNo

48 l 5uslaNo 5uslaNo

49 IV. Bond strength A. bond strength is the energy needed to break a covalent bond 1.Bond length and atom size help determine bond strength a. The shorter the bond length The greater the bond strength i. single bond – longest length ii. Double bond – medium length iii triple bond – shortest length WHICH HAS THE GREATEST BOND STRENGTH?

50 B. Energy is needed to create and break a covalent bond. 1.Energy is released when a covalent bond forms 2. Bond dissociation energy- is needed to break a bond a. always a positive number i. It takes 159KJ/mol to break F 2 Would it take more or less to break N 2 - why?

51 V. Chemical reaction energy A. Endothermic reaction – energy is needed 1. More energy is needed to break the bond than is needed to create new bond. AB + energy  A + B NH 4 SCN + Ba(OH) + energy ( freezes to wood because heat is pulled from the reaction

52 B. Exothermic reaction – energy is released 1. more energy is released when bonds form than is needed to break bonds A + B  AB + energy CaCl + baking soda and water energy is released as heat Hw: pg

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54 I. Naming compounds A. Two types 1. Ionic - metal and non metal or polyatomics. 2. Covalent- we will just learn the rules for 2 non-metals.

55 Covalent compounds l Two words, with prefixes. l Prefixes tell you how many. l mono, di, tri, tetra, penta, hexa, Hepta, octa, nona, deca l First element whole name with the appropriate prefix, except mono. l Second element, -ide ending with appropriate prefix. l Practice

56 Writing Formulas l Two sets of rules, ionic and covalent l To decide which to use, decide what the first word is. l If is a metal or polyatomic use ionic. l If it is a non-metal use covalent.

57 PREFIXES l Mono - one l di - two l Tri- three l Tetra- four l penta- five l hexa- six l Hepta- seven l Octa - eight l nona - nine l deca - ten

58 l CO 2 l CO l CCl 4 lN2O4lN2O4 l XeF 6 lN4O4lN4O4 l P 2 O 10 Naming Covalent Compounds

59 Covalent compounds l The name tells you how to write the formula l Sulfur dioxide l diflourine monoxide l nitrogen trichloride l diphosphorus pentoxide l Work on naming ditto

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61 I. Acids l Substances that produce H + ions when dissolved in water. l All acids begin with H. l Two types of acids: l Oxyacids l Non Oxyacids- Binary Acids

62 A. Binary Acids l 1. Binary Acids( Hydrogen and one other element –A. hydro + element name + IC + acid –Examples –1. HCl- –2. HF- 3. HBr-

63 B. Oxyacids l 1. oxyacids- (hydrogen + oxyanions) –a. name anion + (ic or ous) + acid i. use of ic or ous depends on the number of oxygen atoms in the oxyanion Examples: HNO 3- nitric acid HNO 2 –Nitrous acid H 3 PO 4- phosphoric acid H 2 PO 3 phosphorous acid HC 2 H 3 O 2 – acetic acid

64 l H 2 SO 4 l sulfuric acid l H 2 SO 3 sulfurous acid

65 Formulas for acids l hydrofluoric acid- HF l carbonic acid- H 2 CO 3 l hydrosulfuric acid l phosphorous acid

66 Hydrates l Some salts trap water crystals when they form crystals. l These are hydrates. l Both the name and the formula needs to indicate how many water molecules are trapped. l In the name we add the word hydrate with a prefix that tells us how many water molecules.

67 Hydrates l In the formula you put a dot and then write the number of molecules. Calcium chloride dihydrate = CaCl 2  2  Chromium (III) nitrate hexahydrate = Cr(NO 3 ) 3  6H 2 O

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69 I. Resonance A. When more than one dot diagram with the same connections are possible. 1. SO 2 l Which one is it? l Does it go back and forth. l It is a mixture of both, like a mule. l

70 20 Oct 97Bonding and structure (2)70 Sulfur Dioxide, SO 2 These equivalent structures are called: RESONANCE STRUCTURES. The proper Lewis structure is a HYBRID of the two. Each atom has OCTET..... BUT there is a +1 and -1 formal charge + —— + Rules 1-3  O—S —O

71 Draw the resonance structure O 3 SO 3 SO 2

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

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

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

76 How do we know l Have to draw the diagram and see what happens. l Often happens with polyatomic ions and acids. l Work on drawing lewis structures from packet

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