Double Bond: C - Department of Chemistry | Texas A&M … · · 2005-10-263 Double Bond: C 2H 4...
-
Upload
nguyendieu -
Category
Documents
-
view
217 -
download
4
Transcript of Double Bond: C - Department of Chemistry | Texas A&M … · · 2005-10-263 Double Bond: C 2H 4...
1
Double Bond: C2H4An sp2 hybridized C atom has one electron in each of the three sp2 lobes
Top view of the sp2 hybrid
Side view of the sp2 hybrid + the unhybridized p orbital
2
Two sp2 hybridized C atoms plus p-orbitals in proper orientation to form a C=C double bond
Double Bond: C2H4
3
Double Bond: C2H4
The portion of the double bond formed from the head-on overlap of the sp2
hybrids is designated as a σ bondThe other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a π bond
5
The unhybridized p orbitals form two π bondsNote that a triple bond consists of one σ and two π bonds
Triple Bond: C2H2
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– anionsin aqueous solutions
These two statements represent the Arrhenius theory of acids and bases
8
The BrØnsted-Lowry TheoryThis 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)
acidbase
Notice, that according to the Arrhenius theory NH3 is not a base
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(H2O)n+
Where n is a small integer
We normally write the hydrated hydrogen ion as H3O+ and call it the hydroniumhydronium ionion
10
The BrØnsted-Lowry TheoryAcid-base reactions are the transfer of a proton from an acid to a base
NH3(aq) + HCl(aq) → NH4+(aq) + Cl–(aq)
acidbase
HCl(aq) + H2O(l) → H3O+(aq) + Cl–(aq)acid base
11
Conjugate Acid-Base Pairs
Two species that differ by a proton are called conjugate acidconjugate acid--base pairsbase pairsSuch conjugate pairs will exist for each acid-base reaction
HF(aq) + H2O(l) → H3O+(aq) + F–(aq)acid baseHF is a weak acid and it does not ionize completely in aqueous solutionsThis reaction also proceeds in the reverse direction (it is reversible)
acid base
12
Conjugate Acid-Base Pairs
To find a conjugated base:Add 1 proton (H+) to the acidIncrease the total charge by 1
To find a conjugated acid:Remove 1 proton from the baseDecrease the total charge by 1
H2OCH3COOH
NH3
CH3COO–
13
Conjugate Acid-Base Pairs
acid1 base2
HF is a weak acid and ionizes only slightlyIt 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 H2OH3O+(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)
acid2 base1
HF(aq) + H2O(l) H3O+(aq) + F–(aq)
14
The BrØnsted-Lowry Theory
Important conclusion:Weak acids have strong conjugate basesWeak bases have strong conjugate acids
The weaker the acid or base, the stronger the conjugate partner
Another example: ammonia in water
15
Properties of Acids
Solutions of acids have a sour tasteDon’t taste them in the lab !!!
They change the colors of many indicators
Acids turn blue litmus to redAcids turn bromothymol blue from blue to yellow
They react with metals to generate hydrogen gas, H2
16
Displacement ReactionsDisplacement reactions occur when one element displaces another element from a compound:
Zn + H2SO4 → ZnSO4 + H2
Not all the metals are capable of displacing hydrogen from an acid
Total and net ionic equations:
17
Metal Activity Series
Active enough to displace hydrogen from an acid
Li, K, Ca, Na, Mg, Al, Li, K, Ca, Na, Mg, Al, MnMn, Zn, Fe, Co, Ni, , Zn, Fe, Co, Ni, PbPb,, H, Cu, Hg, Ag, Pt, AuCu, Hg, Ag, Pt, Au
Cannot displace hydrogen from an acid
More active
Less active
18
Write reactions between the following metals and HCl solution. Write total and net ionic equations in each case
Fe, Na, Pt, Ni, Cu
Example 1
19
Write reactions between the following metals and HCl solution. Write total and net ionic equations in each case
Fe, Na, Pt, Ni, Cu
Example 1 (continued)
20
Metal Activity SeriesThe more active metal will always displace the less active metal from the solution of its salt:
Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
21
Write reactions between the following substances in aqueous solutions:
Zn + CuSO4
Hg + Fe(NO2)3
Mg + Hg(NO3)2
Al + Fe(NO3)3
Example 2