Transcript Slide 1
Bonding with Chemistry Lewis Dot Structures VSEPR and Molecular Geometry A chemical bond is made by sharing electrons between two atoms to achieve the outer electron configuration of the noble gases. Chemical Bonds Ionic Covalent Polar (dipole moment) Nonpolar Each element has a preferred outer shell electron configuration. An element tends to form enough bonds to achieve the number of electrons corresponding to the nearest noble gas. This is a periodic (repeating) property of each column (family) of elements. So the number of outer shell electrons can be determined from the periodic table: 1 H 2 He 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba 57 La** 72 Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra 89 Ac** 104 Rf 10 5 Ha 106 Sg 107 Ns 108 Hs 109 Mt 110 111 Etc. Lewis dot structures provide a simple means to determine bonding capacity: Bonding requirements for achieving an octet of electrons in the outer orbital: Element Bonds needed C 4 N 3 P 3 or 5 O 2 S 2 or 6 F 1 Cl 1 Br 1 I 1 H 1 VSEPR = valence shell electron pair repulsion theory indicates what molecular geometry we expect. Essential bonding characteristic of carbon atoms: Carbon has 4 outer shell electrons. It needs 4 more to achieve the Neon configuration of 1s22s22p6. It forms 4 bonds total. Never forget this. It will help you a lot!!! Review: How many bonds does hydrogen form? How many bonds does oxygen form? How many bonds does carbon form? What is the molecular geometry of water? What is the molecular geometry of oxygen gas? What is the molecular geometry of CH4? Organic chemistry We begin with Hydrocarbons Hydrocarbons are composed of the elements __________ and __________, just like the name implies. Three major classes of hydrocarbons Alkanes Alkenes Alkynes Speaking of alkanes, alkenes, alkynes, etc: Every subject has its own language. Listen to military people talk and you know this is true! Organic chemistry is positively loaded with new language to learn. Hang in there, it will come with time… Alkanes aka saturated hydrocarbons Structure Names = nomenclature Properties Physical Chemical Counting the organic way # Carbons 1 2 3 4 5 6 7 8 9 10 Name methane ethane propane butane pentane hexane heptane octane nonane decane We don’t have to stop at C10… for example, C20 is called eicosane. We’ll see that in a later chapter. Melting and boiling points of alkanes 0 -100 287 303 270.5 235.5 253.5 195.9 216.3 174.1 125.7 150.8 68.7 98.4 36.1 -42.1 -0.5 100 -161.5 -88.6 Boiling point (o C) 200 343 28 32 36.8 -57 -54 -150 -188 -138 -130 -100 400 300 -95 -91 -50 -182 -183 Melting point (o C) 0 -5.5 6 10 18 22 -30 -26 -10 50 316.7 330 Straight Chain Alkanes: Boiling points (o C) Straight Chain Alkanes: Melting Points (o C) -200 0 5 10 Number of carbon atoms 15 20 -200 0 5 10 Num ber of carbon atom s 15 20 Cycloalkanes Structural features Nomenclature Properties: similar to noncyclic alkanes Alkenes aka unsaturated hydrocarbons Structural features Nomenclature Properties Physical Chemical Melting and boiling points of alkenes Alkenes: Melting points (o C) Alkenes: Boiling points (o C) 150 0 94 -20 100 Boiling point (o C) Melting point (o C) -40 -60 -80 -106 -100 -119 -120 -139 -140 -140 -165 -169 -160 -138 -185 -185 3 4 50 3.7 0.9 31 30 63 0 -47 -6.3 -50 -100 -151 -150 -180 -200 -200 0 1 2 5 Number of carbon atoms 6 7 8 0 1 2 3 4 5 Number of carbon atoms 6 7 8 Alkynes aka unsaturated hydrocarbons Structural features Nomenclature Properties Physical Chemical More families of organic compounds: When we introduce other atoms than carbon and hydrogen into hydrocarbons, we call these functional groups. They have their own special names. Examples of functional groups: CH3 CH3 H3C C C OH OH CH3 H3C CH3 CH3 Cl OH OH O O Cl Cl ibuprofen O 11 H 12 More examples of functional groups in molecules: O N OH HO HO OH O O O O O O erythromycin OH O Review: Chemical bonding re: carbon compounds How many bonds? Three major classes of hydrocarbons 1. 2. 3. Counting the organic way: Recognizing functional groups Problems to practice on: Chapter 11 & Chapter 12: check out the chapter problems sheet for recommended problems for practice.