Double Bond: C2H4

1
Double Bond C2H4

• An sp 2 hybridized C atom has one electron in
  each of the three sp 2 lobes

Side view of the sp 2 hybrid the unhybridized
p orbital
Top view of the sp 2 hybrid
2
Double Bond C2H4

• Two sp 2 hybridized C atoms plus p -orbitals in
  proper orientation to form a CC double bond

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Double Bond C2H4

• The portion of the double bond formed from the
  head-on overlap of the sp 2 hybrids is designated
  as a s bond
• The other portion of the double bond, resulting
  from the side-on overlap of the p orbitals, is
  designated as a p bond

4
Triple Bond C2H2

• A ? bond results from the head-on overlap of two
  sp hybrid orbitals

5
Triple Bond C2H2

• The unhybridized p orbitals form two p bonds

• Note that a triple bond consists of one ? and two
  p bonds

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CHAPTER 10

• Reactions in Aqueous Solutions I Acids, Bases,
  and Salts

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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

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

NH3(aq) H2O(l) ? NH4(aq) OH(aq)
acid
base

• Notice, that according to the Arrhenius theory
  NH3 is not a base

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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 dont know exactly how many
• H(aq) is really H(H2O)n
• Where n is a small integer
• We normally write the hydrated hydrogen ion as
  H3O and call it the hydronium ion

10
The BrØnsted-Lowry Theory

• Acid-base reactions are the transfer of a proton
  from an acid to a base

NH3(aq) HCl(aq) ? NH4(aq) Cl(aq)
acid
base
HCl(aq) H2O(l) ? H3O(aq) Cl(aq)
acid
base
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Conjugate Acid-Base Pairs
HF(aq) H2O(l) ? H3O(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

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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

H2O
NH3
CH3COO
CH3COOH
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Conjugate Acid-Base Pairs
HF(aq) H2O(l) H3O(aq) F(aq)
acid1
base2
acid2
base1

• 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 H2O (it holds the proton stronger)
• Another way to put it is to say that F(aq) is a
  stronger base than H2O
• H3O(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)

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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

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Properties of Acids

• Solutions of acids have a sour taste
• Dont 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,
  H2

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Displacement Reactions

• Displacement reactions occur when one element
  displaces another element from a compound

Zn H2SO4 ? ZnSO4 H2

• Total and net ionic equations

• Not all the metals are capable of displacing
  hydrogen from an acid

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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

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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

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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

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Metal Activity Series

• The more active metal will always displace the
  less active metal from the solution of its salt

Cu 2AgNO3 ? Cu(NO3)2 2Ag
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Example 2

• Write reactions between the following substances
  in aqueous solutions
• Zn CuSO4
• Hg Fe(NO2)3
• Mg Hg(NO3)2
• Al Fe(NO3)3

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Example 2 (continued)
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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)