Chemical Forces Bonding

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Chemical ForcesBonding Interactions

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

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Chemical Forces
The interaction of atoms, ions
molecules depends on
charge attraction and the interaction of valence
electrons with other nuclei.
distance between the species.
direction between the species.
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How Big Is an Atom?
van der Waals radii - no bonding, atoms just
touching
value may depend on substituent effects and
crystal packing forces
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How Big Is an Atom?
ionic radii - equilibrium distance between
strong Coulombic attraction and repulsion of core
electrons
d rA rB
Why are ionic radii hard to determine?
d
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How Big Is an Atom?
covalent radii - half the distance of identical
atoms
- approximate radius of core electrons
d rA rB
C - C 154/2 77 pm F - F 142/2 71
d
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How Big Is an Atom?
ionic resonance - shortened covalent distance due
to electronegativity differences
d rA rB - 9 ??
d rA rB - 7(??)2
C - C 154/2 77 pm F - F 142/2 71 C - F 136
d
C - F 77 71 - 9(4.0-2.5) 134 77
71 - 7(4.0-2.5)2 132
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Types of Chemical ForcesCovalent Bonding
Directional
H - H 432 kJmol-1 C - C 346 N - N 167 F -
F 155 P - P 200
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Types of Chemical ForcesIonic Bonding
Non-directional
similar in strength to covalent bonding
? F dr
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Types of Chemical ForcesIon Dipole
attraction of a polar molecule to a charged
species
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Types of Chemical ForcesDipole - Dipole
polar liquid structure to be stable, must be
stronger than kT (8.314 Jmol-1K-1)(298 K)
2.5 kJmol-1
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Types of Chemical Forces
Induced Dipole - polarization of the electron of
a non-polar species by a species with a dipole.
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If noble gases have a complete shell of
electrons and no dipole moment, why do they
liquefy or solidify?
momentary imbalance of electron density around a
nonpolar atom or molecule. Causes a momentary
polarization of an electron in an adjacent
molecule or atom.
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Hydrogen Bonding
H bound to a very electronegative atom
is attracted to another very electronegative atom.
N
O
B
C
F
Ne
5-160 kJmol-1, typically 20-25 kJmol-1
P
S
Al
Si
Cl
Ar
CN
As
Se
Ga
Ge
Zn
Cu
Br
Kr
Sb
Te
In
Sn
Cd
Ag
I
Xe
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Hydrogen Bonding
Influences mp, bp, density
Covalent electrostatic effects
-

dipole-dipole dipole-ion
delocalization of e- density resonance
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Hydrogen Bonding
usually linear usually asymmetric, but symmetric
examples occur
F-H-F-
dF-F 240 pm
dH-F 120 pm
DHrx -161 kJmol-1
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Hydrogen BondingHydrates and Clathrates
Hydrates
waters of hydration
CaSO4 (anhydrous)
CaSO4 ½ H2O (Plaster of Paris)
CaSO4 2 H2O (gypsum)
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Hydrogen BondingHydrates and Clathrates
Hydrates
waters of hydration
CuSO4 (anhydrous) white 0.6 M
CuSO4 5 H2O blue 1.2 M
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CuSO45H2O
sulfate ions occupy the axial positions
water molecules are square planar around the
copper(II) ion
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CuSO45H2O
one water molecule per formula unit bridges
between the sulfate ions
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CuSO45H2O
When the sample is heated to 215 C
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CuSO45H2O
When the sample is heated to 330 C
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Hydrogen BondingHydrates and Clathrates
Hydrates
thermogravimetric analysis
CuSO4 5 H2O
Temp
mass
96
65 C
? loss of 4 H2O
71
215 C
? loss of 5 H2O
64
330 C
64
390 C
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Physical PropertiesMelting and Boiling
compare
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Physical PropertiesSolubility
All nitrates are soluble in water.
What factors are involved in dissolution?
M(NO3)n(s) H20(l) Mn(aq) n NO3-(aq)
lattice energy
hydrogen bonding
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Clathrates and Sepulchrates
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Physical PropertiesMolar Solubility - Hydrated
Salts
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