Double Bond: C 2 H 4. An sp 2 hybridized C atom has one electron in each of the three sp 2 lobes

Transcription

1 Double Bond: C 2 H 4 An sp 2 hybridized C atom has one electron in each of the three sp 2 lobes Top view of the sp 2 hybrid Side view of the sp 2 hybrid + the unhybridized p orbital 1

2 Double Bond: C 2 H 4 Two sp 2 hybridized C atoms plus p-orbitals in proper orientation to form a C=C double bond 2

3 Double Bond: C 2 H 4 The portion of the double bond formed from the head-on overlap of the sp 2 hybrids is designated as a σ bond The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a π bond 3

4 Triple Bond: C 2 H 2 A σ bond results from the head-on overlap of two sp hybrid orbitals 4

5 Triple Bond: C 2 H 2 The unhybridized p orbitals form two π bonds Note that a triple bond consists of one σ and two π bonds 5

6 CHAPTER 10 Reactions in Aqueous Solutions I: Acids, Bases, and Salts 6

7 The Arrhenius Theory Acids are substances that contain hydrogen and produce H + cations in aqueous solutions Bases are substances that contain a hydroxyl group and produce OH anions in aqueous solutions These two statements represent the Arrhenius theory of acids and bases 7

8 The BrØnsted-Lowry Theory This theory is more general than the Arrhenius theory An acid is a proton donor (H + ) A base is a proton acceptor NH 3 (aq) + H 2 O(l) NH 4+ (aq) + OH (aq) base acid Notice, that according to the Arrhenius theory NH 3 is not a base 8

9 The Hydronium Ion The protons (H + ) are never present in solution by themselves Protons are always hydrated that is surrounded by several water molecules We don t know exactly how many H + (aq) is really H(H 2 O) n + Where n is a small integer We normally write the hydrated hydrogen ion as H 3 O + and call it the hydronium ion 9

10 The BrØnsted-Lowry Theory Acid-base reactions are the transfer of a proton from an acid to a base NH 3 (aq) + HCl(aq) NH 4+ (aq) + Cl (aq) base acid HCl(aq) + H 2 O(l) H 3 O + (aq) + Cl (aq) acid base 10

11 Conjugate Acid-Base Pairs HF(aq) + H 2 O(l) H 3 O + (aq) + F (aq) acid base acid base HF is a weak acid and it does not ionize completely in aqueous solutions This reaction also proceeds in the reverse direction (it is reversible) Two species that differ by a proton are called conjugate acid-base pairs Such conjugate pairs will exist for each acid-base reaction 11

12 Conjugate Acid-Base Pairs To find a conjugated base: Add 1 proton (H + ) to the acid Increase the total charge by 1 To find a conjugated acid: Remove 1 proton from the base Decrease the total charge by 1 H 2 O CH 3 COOH NH 3 CH 3 COO 12

13 Conjugate Acid-Base Pairs HF(aq) + H 2 O(l) H 3 O + (aq) + F (aq) acid 1 base 2 acid 2 base 1 HF is a weak acid and ionizes only slightly It prefers to exist as HF(aq) rather than F (aq) This means that F (aq) has higher affinity to the proton than H 2 O (it holds the proton stronger) Another way to put it is to say that F (aq) is a stronger base than H 2 O H 3 O + (aq) gives up the proton easier than HF(aq) and therefore it is a stronger acid than HF(aq) (it is more prone to loosing the proton) 13

14 The BrØnsted-Lowry Theory Important conclusion: Weak acids have strong conjugate bases Weak bases have strong conjugate acids The weaker the acid or base, the stronger the conjugate partner Another example: ammonia in water 14

15 Properties of Acids Solutions of acids have a sour taste Don t taste them in the lab!!! They change the colors of many indicators Acids turn blue litmus to red Acids turn bromothymol blue from blue to yellow They react with metals to generate hydrogen gas, H 2 15

16 Displacement Reactions Displacement reactions occur when one element displaces another element from a compound: Zn + H 2 SO 4 ZnSO 4 + H 2 Total and net ionic equations: Not all the metals are capable of displacing hydrogen from an acid 16

17 Metal Activity Series More active Li, K, Ca, Na, Mg, Al, Mn,, Zn, Fe, Co, Ni, Pb, H, Cu, Hg, Ag, Pt, Au Less active Active enough to displace hydrogen from an acid Cannot displace hydrogen from an acid 17

18 Example 1 Write reactions between the following metals and HCl solution. Write total and net ionic equations in each case Fe, Na, Pt, Ni, Cu 18

19 Example 1 (continued) Write reactions between the following metals and HCl solution. Write total and net ionic equations in each case Fe, Na, Pt, Ni, Cu 19

20 Metal Activity Series The more active metal will always displace the less active metal from the solution of its salt: Cu + 2AgNO 3 Cu(NO 3 ) 2 + 2Ag 20

21 Example 2 Write reactions between the following substances in aqueous solutions: Zn + CuSO 4 Hg + Fe(NO 2 ) 3 Mg + Hg(NO 3 ) 2 Al + Fe(NO 3 ) 3 21

22 Example 2 (continued) 22

23 Assignments & Reminders Go through the lecture notes Read Chapter 10 completely Read Section 4-10 of Chapter 4 Monday (10/31) and Tuesday (11/1) lecture quiz #5 (Chapter 8) Homework #5 is due by Monday (10/31) 23