1 Announcements & Agenda (01/31/07) This week’s quiz moved to Friday (Ch 4) Exam NEXT FRIDAY!!! Covers Ch 1-5 Covers Ch 1-5 Intermolecular Forces (Notes + bits & pieces of Ch 6) Intermolecular Forces (Notes + bits & pieces of Ch 6) Ch Ch CHM 103 Lab CHM 103 LabToday Molecular Shapes & Polarity (4.7) Molecular Shapes & Polarity (4.7) Chemical Reactions ( ) Chemical Reactions ( )

2 Last Time: Covalent Bonding

3 Flowchart for Naming Compounds

4 Learning Check Classify as ionic or covalent compounds, then name ’em. ionic Ca 2+ PO 4 3− calcium phosphate ionic Ca 2+ PO 4 3− calcium phosphate ionic Fe 3+ Br − iron(III) bromide ionic Fe 3+ Br − iron(III) bromide covalent 1S 2 Cl sulfur dichloride covalent 2 Cl 1 O dichlorine monoxide covalent 2N(element) nitrogen A. Ca 3 (PO 4 ) 2 B. FeBr 3 C. SCl 2 D. Cl 2 O E. N 2

5 Connecting the Extremes: In Between Ionic and Covalent Bonds (4.6) A pure covalent bond occurs only when two identical atoms are bonded: N 2 Polar Covalent Bond: Unequal sharing between two dissimilar atoms Therefore, the electrons are nearer to one of the atoms, and that atom acquires a partial negative charge (  ). Therefore, the electrons are nearer to one of the atoms, and that atom acquires a partial negative charge (  ). And consequently the other atom has a partial positive charge  And consequently the other atom has a partial positive charge 

6 Some Electronegativity Values for Group A Elements Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Low values High values ` Electronegativity increases Electronegativity increases ` Electronegativity decreases Electronegativity decreases

7 The Two Extremes Revisited… The greater the difference of the EN values, the more polar the bond! An EN difference ≥ 1.8 is considered an ionic bond.

8 occur between nonmetals.occur between nonmetals. have equal or almost equal sharing of electrons.have equal or almost equal sharing of electrons. have almost no electronegativity difference (0.0 to 0.4).have almost no electronegativity difference (0.0 to 0.4). Examples: Electronegativity Electronegativity Atoms Difference Type of Bond N-N = 0.0 Nonpolar covalent Cl-Br = 0.2 Nonpolar covalent H-Si = 0.3 Nonpolar covalent Nonpolar Covalent Bonds

9 occur between nonmetal atoms.occur between nonmetal atoms. have an unequal sharing of electrons.have an unequal sharing of electrons. have a moderate electronegativity difference (0.5 to 1.7).have a moderate electronegativity difference (0.5 to 1.7). Examples: Electronegativity Electronegativity Atoms DifferenceType of Bond O-Cl = 0.5Polar covalent Cl-C = 0.5Polar covalent O-S = 1.0Polar covalent Polar Covalent Bonds

10 Ionic Bonds occur between metal and nonmetal ions.occur between metal and nonmetal ions. form as a result of electron transfer.form as a result of electron transfer. have a large electronegativity difference (1.8 or more).have a large electronegativity difference (1.8 or more). Examples: Electronegativity Electronegativity Atoms Difference Type of Bond Cl-K 3.0 – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs2.5 – 0.7= 1.8 Ionic

11 Shapes & Polarity of Molecules (4.7)

12 Shapes of Molecules 3-D shape affected by the # of atoms and lone pairs around the central atom determine from Lewis Dot Structures determine from Lewis Dot Structures Use VSEPR theory (valence-shell-electron- pair repulsion

13 Using the VSEPR Model 1. Draw the electron-dot structure 2.Count the total # of electron pairs (groups) around central atom IMPORTANT: INCLUDES BOTH LONE PAIRS AND BONDED ATOMS!!!IMPORTANT: INCLUDES BOTH LONE PAIRS AND BONDED ATOMS!!! 3.Predict the electron group geometry (EGG) 4.Predict the shape of the molecule using the # of ATOMS bonded to the central atom

14 Four Electron Groups In a molecule of CH 4, there are 4 electron groups around C.there are 4 electron groups around C. repulsion is minimized by placing four electron groups at angles of 109°, which is a tetrahedral arrangement.repulsion is minimized by placing four electron groups at angles of 109°, which is a tetrahedral arrangement. the shape with four bonded atoms is tetrahedral.the shape with four bonded atoms is tetrahedral. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

15 Three Bonding Atoms & 1 Lone Pair In a molecule of NH 3, 3 electron groups bond to H atoms and the 4 one is a lone (nonbonding) pair.3 electron groups bond to H atoms and the 4 one is a lone (nonbonding) pair. repulsion is minimized with 4 electron groups in a tetrahedral arrangement.repulsion is minimized with 4 electron groups in a tetrahedral arrangement. with three bonded atoms, the shape is pyramidal.with three bonded atoms, the shape is pyramidal.

16 2 Bonding Atoms & 2 Lone Pairs In a molecule of H 2 O, two electrons groups are bonded to H atoms and two are lone pairs (4 electron groups).two electrons groups are bonded to H atoms and two are lone pairs (4 electron groups). four electron groups minimize repulsion in a tetrahedral arrangement.four electron groups minimize repulsion in a tetrahedral arrangement. the shape with two bonded atoms is bent(~109  ).the shape with two bonded atoms is bent(~109  ).

17 Electron Group Bonded Atoms Lone Pairs Bond Angles Molecular Shape Example440109tetrahedral CH 4 431~109Pyramidal NH 3 422~109Bent H2OH2OH2OH2O Shapes with 4 Electron Groups Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

18 Learning Check State the number of electron groups, lone pairs, and use VSEPR theory to determine the shape of the following molecules or ions. 1) tetrahedral 2) pyramidal3) bent A. PF 3 B. H 2 S C. CCl 4

19 Solution A. PF 3 4 electron groups, 1 lone pair, (2) pyramidal B.H 2 S 4 electron groups, 2 lone pairs, (3) bent C. CCl 4 4 electron groups, 0 lone pairs, (1) tetrahedral

20 Polar Molecules contain polar bonds.contain polar bonds. have a separation of positive and negative charge called a dipole indicated with  + and  -.have a separation of positive and negative charge called a dipole indicated with  + and  -. have dipoles that do not cancel!have dipoles that do not cancel!  +  -  +  - H–Cl H — N — H dipole dipole dipoles do not cancel dipoles do not cancel H

21 Nonpolar Molecules A nonpolar molecule contains nonpolar bonds.contains nonpolar bonds. Cl–Cl H–H Cl–Cl H–H or has a symmetrical arrangement of polar bonds.or has a symmetrical arrangement of polar bonds. O=C=O Cl Cl–C–Cl Cl–C–Cl Cl Cl dipoles cancel dipoles cancel

22 Determining Molecular Polarity STEP 1: Write the electron-dot formula. STEP 2: Determine the polarity of the bonds. STEP 3: Determine if dipoles cancel. Example: H 2 O.... H─O : H 2 O is polar │ H dipoles do not cancel

23 Learning Check Identify each of the following molecules as 1) polar or 2) nonpolar. A. HBr B. Br 2 C. SiBr 4

24 Solution Identify each of the following molecules as 1) polar or 2) nonpolar. A. HBrlinear; one polar bond (dipole); polar B. Br 2 linear; nonpolar bond; nonpolar C. SiBr 4 tetrahedral; dipoles cancel; nonpolar

25 A couple more keypad questions to close out Chapter 4.

26 What type of bond would form between a Carbon atom and an Oxygen atom? 1.Nonpolar covalent 2.Polar covalent 3.Ionic 4.C and O can’t ever form bonds 12345

27 In a molecule of Oxygen (O 2 ), the atoms are joined by a: 1.Single bond 2.Double bond 3.Triple bond 4.Quadruple bond 12345

28 Chapter 5!!! Chemical Reactions

29 Chemical Change reacting substances form new substances with different compositions and properties.reacting substances form new substances with different compositions and properties. a chemical reaction takes place.a chemical reaction takes place. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

30 Physical Change the identity and composition of the substance do not change.the identity and composition of the substance do not change. the state can change or the material can be torn into smaller pieces.the state can change or the material can be torn into smaller pieces. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

31 Examples of Chemical and Physical Changes

32 Chemical Reaction old bonds are broken & new bonds are formed.old bonds are broken & new bonds are formed. atoms in the reactants are rearranged to form one or more different substances.atoms in the reactants are rearranged to form one or more different substances. Fe and O 2 form rust (Fe 2 O 3 ).Fe and O 2 form rust (Fe 2 O 3 ).

33 Chemical Equations Chemical Equations Gives the chemical formulas of the reactants on the left of the arrow and the products on the right. Reactants Product Reactants Product C(s) O 2 (g) CO 2 (g)

34 Symbols Used in Equations the states of the reactants.the states of the reactants. the states of the products.the states of the products. the reaction conditions.the reaction conditions. TABLE 5.2

35 Chemical Equations are Balanced In a balanced chemical reaction atoms are not gained or lost.atoms are not gained or lost. the # of reactant atoms is equal to the number of product atoms.the # of reactant atoms is equal to the number of product atoms.

36 Quick check…. Determine if each equation is balanced or not. A. Na(s) + N 2 (g)  Na 3 N(s) No. 2 N on reactant side, 1 N on product side. No. 2 N on reactant side, 1 N on product side. 1 Na on reactant side, 3 Na on product side. 1 Na on reactant side, 3 Na on product side. B. C 2 H 4 (g) + H 2 O(l)  C 2 H 5 OH(l) Yes. 2 C = 2 C Yes. 2 C = 2 C 6 H = 6 H 6 H = 6 H 1 O = 1 O 1 O = 1 O

37 Guide to Balancing a Chemical Equation: Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

38 To balance the following equation, Fe 3 O 4 (s) + H 2 (g)  Fe(s) + H 2 O(l) work on one element at a time.work on one element at a time. use only coefficients in front of formulas.use only coefficients in front of formulas. do not change any subscripts.do not change any subscripts. Fe:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + H 2 O(l) O:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g)  3Fe(s) + 4H 2 O(l) Steps in Balancing an Equation

39 1. Write the equation with the correct formulas. NH 3 (g) + O 2 (g)  NO(g) + H 2 O(g) NH 3 (g) + O 2 (g)  NO(g) + H 2 O(g) 2. Determine if the equation is balanced. No, not all atoms are balanced. 3. Balance with coefficients in front of formulas. 4NH 3 (g) + 5O 2 (g)  4NO(g) + 6H 2 O(g) 4. Check that atoms of each element are equal in reactants and products. 4 N (4 x 1 N) = 4 N (4 x 1 N) 4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O)= 10 O(4 O + 6 O) 10 O (5 x 2 O)= 10 O(4 O + 6 O) Balancing Chemical Equations

40 Equations with Polyatomic Ions

41 Balancing with Polyatomic Ions MgCl 2 (aq) + Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance PO 4 3- as a unit MgCl 2 (aq) + 2Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) MgCl 2 (aq) + 2Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 2 PO 4 3- = 2 PO PO 4 3- = 2 PO 4 3- Balance Mg and Cl 3MgCl 2 (aq) + 2Na 3 PO 4 (aq)  6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 3 Mg 2+ = 3 Mg 2+ 3 Mg 2+ = 3 Mg 2+ 6 Na + = 6 Na + 6 Na + = 6 Na + 6 Cl - = 6 Cl - 6 Cl - = 6 Cl -