Chapter 13: Phenomena

Transcription

1 Chapter 13: Phenomena Phenomena: Scientists measured the bond angles of some common molecules. In the pictures below each line represents a bond that contains 2 electrons. If multiple lines are drawn together these are double or triple bonds and contain 4 and 6 electrons respectively. What patterns do you notice from the data? a) b) Cl c) H N H Cl C Cl H Cl Bond Angles: 107 d) Bond Angles: 105 g) F B Bond Angles: 120 Bond Angles: e) Bond Angles: 120 h) C Bond Angle: 117 H N H N H C C H + Bond Angles: f) Bond Angles: 119 i) Bond Angles: 180 j) S H Bond Angles: 180

2 Chapter 13 Bonding: General Concepts Big Idea: Bonds are formed from the attraction between oppositely charged ions or by sharing electrons. nly the valence electrons participate in bonding. The shape of the molecules maximize the distance between areas of high electron density. o Types of Bonding o Electronegativity o Lewis Structures o Strength/Length of Covalent Bonds o Shapes of Molecules (VSEPR) o Polar Molecules 2

3 Lewis Structure Review Drawing Lewis Structures that bey the ctet Rule C 3 2-1(C) 3() 2(e - ) Total Step 1: (Determine Valence e - ) Step 2: (Determine Wanted e - ) Step 3: Determine number of bonds # bonds = wanted valence 2 Step 4: Determine number of electrons # e = valence 2 bonds 3

4 Lewis Structure Review Resonance: A blend of Lewis structures into a single composite hybrid structure C C C Formal Charge = Valence e - e - Surrounding Atom Note: Loan pairs count for 2 e - and bonds count for 1 e C 4

5 Lewis Structure Review Drawing Lewis Structures that Minimize Formal Charges (nly atoms in period 3 and later can expand their octets) S 2 1(S) 2() Total Step 1: (Determine Valence e - ) Step 2: Find structure with lowest formal charges 5

6 VSEPR (Valence-Shell Electron-Pair Repulsion Model): Extends Lewis s theory of bonding to account for molecular shapes by adding rules that account for bond angle. Rule 1: Regions of high electron concentration (bonds and lone pairs on the central atom) repel one another and to minimize their repulsion, these regions move as far apart as possible while maintaining the same distance from the central atom. Rule 2: There is no distinction between single and multiple bonds: a multiple bond is treated as a single region of high electron concentration. 6

7 Rule 3: All regions of high electron density, lone pairs and bonds, are included in a description of the electronic arrangement, but only the positions of atoms are considered when reporting the shape of a molecule (molecular shape). Rule 4: The strengths of repulsion are in the order lone pair lone pair > lone pair atom > atom atom. 7

8 Assigning Shape and Bond Angles of Molecules Step 1: Draw the Lewis structure. Step 2: Assign the electronic arrangement around the central atom (linear, trigonal planer, tetrahedral) Note: Electronic arrangement includes all areas of electron density (lone pairs and bonds). Step 3: Identify the molecular shape (linear, bent, trigonal planer, trigonal pyramidal, tetrahedral) Note: Molecular shape includes only bonds. Step 4: Figure out the bond angle (allow for distortion) 8

9 Possible Electronic Arrangements 9

10 Possible Molecular Arrangements The names of the shapes of simple molecules and their bond angles. Lone pairs of electrons are not shown. 10

11 2 Areas of Electron Density 3 Areas of Electron Density No Lone Pairs Linear No Lone Pairs Trigonal Planar 1 Lone Pair Bent 4 Areas of Electron Density No Lone Pairs Tetrahedral 1 Lone Pair Trigonal Pyramidal 2 Lone Pairs Bent 11

12 5 Areas of Electron Density No Lone Pairs Trigonal Bipyramidal 1 Lone Pair Seesaw 2 Lone Pairs T-Shaped 3 Lone Pair Linear 12

13 6 Areas of Electron Density No Lone Pairs ctahedral 1 Lone Pair Square Pyramidal 2 Lone Pairs Square Planer 3 Lone Pairs T-Shaped 4 Lone Pair Linear 13

14 Step 1: Draw Lewis Structure CH 4 1(C) 4(H) Total Valence e - Wanted e - Determine number of bonds # bonds = wanted valence 2 Determine number of electrons # e = valence 2 bonds Step 2: Determine Electronic Shape Step 3: Determine Molecular Shape Step 4: Determine Angle 14

15 Step 1: Draw Lewis Structure (beys ctet Rule) S 3 2-1(S) 3() 2(e - ) Total Valence e - Wanted e - Determine number of bonds # bonds = wanted valence 2 Determine number of electrons # e = valence 2 bonds Step 2: Determine Electronic Shape Step 3: Determine Molecular Shape Step 4: Determine Angle 15

16 Student Question What is the most likely shape of ICl 4-? Helpful Hint: Make sure that your formal charges are minimized. a) ctahedral b) Trigonal Planar c) Seesaw d) Tetrahedral e) None of the Above 16

17 Polar Molecules Student Question Is PCl 4- polar or nonpolar? Helpful Hint: Make sure that your formal charges are minimized. a) Polar b) Nonpolar 17

18 Take Away From Chapter 13 Big Idea: Bonds are formed from the attraction between oppositely charged ions or by sharing electrons. nly the valence electrons participate in bonding. The shape of the molecules maximize the distance between areas of high electron density. Lewis Structures Be able to draw Lewis structures of covalent compounds. (57,58) Know how to calculate formal charges.(78,79) Identification of most likely Lewis structure. Know when multiple resonance structures are possible for a compound.(60,61,65,73) Know when atoms can expand their octets (group 3 and greater).(80) 18 Numbers correspond to end of chapter questions.

19 Take Away From Chapter 13 Shape of Molecules (VSEPR) (88,91) Know how to determine electronic shape. Linear, trigonal planar, tetrahedral, trigonal bipyramidal, or octahedral. Know how to determine molecular shape. Linear, angular, trigonal planar, trigonal pyramidal, T- shaped, tetrahedral, seesaw, square planar, trigonal bipyramidal, square pyramidal, or octahedral. Know how to determine bond angles. Polar Molecules Be able to determine if a molecule is polar or non polar. (93,94) 19 Numbers correspond to end of chapter questions.