Ochem ch 2
Terms
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- Constructive Interference
- Two waves in same phase
- Destructive Interference
- Two waves in different phase
- Dual Nature of light
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Light undergous both interference and diffraction: wavelenth
Photoelectric effect behaves like a massless paprticle: photon - Lambda
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Wavelength= h/(mass x velocity)
where h is Plancks constant - De Broglie
- Proved photon nature of light
- Davisson and Germer
- Beam of e- showed deffraction by Al foil: wavelike property
- Line (band) spectrum
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Plot amout of light absorbed or emitted by substance versus wavelength of light
Corresponds to photons of certain energies of light - Neils Bohr
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Postulated E levels of e were quantized
when an atom gives off an electron it moves into a higher level - Orbital
- The prob of finding an e- around the nucleus ina region of space
- 1s
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N=1 l=o
symmetrically positive or negative with high prob at nucleus and exponentially lower with distance - 2s
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N=2 and l=0
Middle looks like 1s with a node and then a raise and fall in density - 2p
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N=2 and l=1
Nodal plain in nucleus, density raises and then falls back down - Linear Combination of Atomic Orbitals
- Normal covalent bonds half filled orbitals overlap sharing e- and forming bonding molecular orbitals and antibonding orbitals
- Sigma bond
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symmetrical about its axis
Overlapping two s forms sigma and sigma* orbitals
End to end overlap of 2 p orbitals forms pi and pi* - Valence Shell Electron Pair Repulsion Theory (VSEPR theory)
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In covalent molecules both bonded and lone pairs of e- repel eachother
Molecules assume shape to keep all e- as far away frome each other as possible
Solid straight line is on plane
Solid Wedge towards reader
dash wedge away from reader - Linear
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180°
Two atoms bound to central atom, no lone pair - Bent
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105°
Two atoms bound to central atom with lone pair - Triangular planar
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120°
Three atoms bound to central atom with no lone pair - Pyramidal
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107.5°
three atoms bound to central atom w/lone pair - Tetrahedral
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109.5°
Four atoms bount to central atom w/no lone pair - Bipyramidal
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Five atoms bound to central atom w/no lone pair
Three atoms on (XY) plane, centtral one is on (XZ) plane with other two - Octahedral
- Six atoms bound to central atom with no lone pair
- Hybridization
- Mixing of wave equations to form new orbitals with different directions in space from the original atomic orbitals
- sp^3 hybrid
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4 new orbitals from 2s with three 2p
points to corners of regular tetrahedron w/bond angles 109.5°
lower E than original - sp^2 hybrid
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3 new orbitals from 2s and 2 2p orbitals
Planar 120° w/perpindicular P orbital
lower E than original - sp hybrid
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2 new orbitals from 2s and 1 2p
lower E than original - Polar bonds
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Bond has significant dipole
unequal sharing of e- - δ+/δ-
- Partial plus (< full +1 ion charge) or partial minus (< full -1 electron charge) dipole charge
- Some dipole moments (many)
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C-N .22 D (All in D)
C-H .3
C-0 .86
H-I 1.29
H-B 1.48
H-4 1.51
H-CL 1.56
C=0 2.4
C=-N 3.6 - Dipole moment
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Net vector sum of individual dipole moment
= partial charge (coulambs) x dostance between atoms (m) - Debye
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Conversion factor for dipole moment
3.34 x 10^-30 coulomb meters - u in debye units
- 4.8 x [delta electron charge] x [distance in angstroms]
- net dipole moment = 0
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No molecular polarity
FF
CO2
BF3
CCl4 - Stereoisomer polarity
- One may be polar while other is non-polar
- Repulsive intramol forces
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electrons repel each other or nuclei repel each other when too close
Steric hindrance occurse when molecules come to close to each other and are in each others way - Attractive intromol forces
- positive nucleus attracts electrosn
- Dipole-Dipole
- Attraction of permanent dipoles
- Hydrogen Bonding
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Special case of strong dipole-dipole bonding with H attached to N, O or F
Carbonyl H not usually H bond
Strength ~5-6 kcal/mol - London Forces
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Very weak intermol forces netween molecules due to temporary dipoles
In non-p;olar bonds e- temp move closer to one atom creating a dipole
inducers short lived dipole
formation in a neighboring
molecule
Increases with surface area - Strong Intermolecular forces vs bp and mp
- bp and mp raised by stronger forces
- Solubility of Polar and ionic substances
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dissolve in very polar solvent (ie water, ethyl alc)
Anions H-bond to water and alcohols
Cations attracted to lone pairs or partial negatives - ΔG = ΔH - TΔS
- s is entropy (disorder), h is enthalpy
- Salt in water
- ΔH is small positive b//c energy is required to seperate Na from Cl but some E is given off by formation of H bonds to cl and the ion-dipole attraction of Na+ for the O of water
- Ionic substance in non-polar solvent
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Does not dissolve, attraction of Na to Cl strong and weak london forces of non-polar solvent not enough to break bonds
ΔH is large positive - Small alcohols in water
- misciple with water due to H bonding and increase in S