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Chem 122 Exam 1

Terms in this set (60)

valence bond theory
a model that attempts to reconcile the shapes of molecules with those of atomic orbitals through the concepts of orbital overlap and hybridization
1. opposing spins of the electron pair
2. maximum overlap of bonding orbitals
3. hybridization of atomic orbitals
4. features of hybrid orbitals
hybridization
a postulate process of orbital mixing to form hybrid orbitals
hybrid orbitals
an atomic orbital postulated to form during bonding by the mathematical mixing of specific combinations of nonequivalent orbitals in given atom
sp
linear, 180
sp2
trigonal planar, 120
sp3
tetrahedral, 109.5
sp3d
trigonal bipyramidal, 90, 120
sp3d2
octahedral, 90
sigma bond
a type of covalent bond that arises through end-to-end orbital overlap and has most of its electron density along an imaginary line joining the nuclei. has the highest electron density along the bond axis
pi bond
a covalent bond formed by sideways overlap of two atomic orbitals that has two regions of electron density, one above and one below the internuclear axis
molecular orbital theory
a model that describes a molecule as a collection of nuclei and electrons in which the electrons occupy orbitals that extend over the entire molecule
bonding MO
a molecular orbital formed when wave functions are added to each other, which increases electron density between the nuclei. Electrons occupying such an orbital stabilize the molecule. nuclear repulsions decrease while nucleus-electron attractions increase. lower in energy than the AOs
antibonding MO
a molecular orbital formed when wave functions are subtracted from each other, which decreases electron density between the nuclei and leaves a node. Electrons occupying such an orbital destabilize the molecule. Higher in energy than the AOs. nuclear repulsions increase.
sigma MOs
a molecular orbital that is cylindrically symmetrical about an imaginary line that runs through the nuclei of the component atoms.
molecular orbital diagram
a depiction of the relative energy and number of electrons in each MO, as well as the atomic orbitals from which the MOs form
MO bond order
the number of electrons in bonding MOs minus the number in antibonding MOs, divided by two. if BO > 0 - molecule is more stable than separate atoms and will form. if BO = the molecule is as stable as the separate atoms and will not form. the higher the bond order, the stronger the bond
pi MOs
a molecular orbital formed by combination of two atomic (usually p) orbitals whose orientations are perpendicular to the internuclear axis
not mixing 2s + 2p
O2, F2, Ne2
pi2p, sigma 2p, pi 2p, sigma 2p
mixing 2s +2p
B2, C2, N2
sgma2p, pi2p, pi2p, sigma2p
paramagnetic
unpaired electrons
diamagnetic
all paired electrons
nonbonding MOs
a molecular orbital tat is not involved in bonding
in polar covalent molecules, bonding _____ are closer in energy to the _____ of the more electronegative atom
MOs, AOs
phase
a physically distinct ad homogeneous part of a system
intermolecular forces
the attractive and repulsive forces among the particles - molecules, atoms, or ions - in a sample of matter
phase changes
a physical change from one phase to another, usually referring to a change in physical state
Coulomb's law
the electrostatic potential energy depends on the charges of the particles and the distances between them
gas
conforms to the shape and volume of a container
high compressibility
high ability to flow
liquid
conforms to the shape of container, volume limited by surface
very low compressibility
moderate ability to flow
solid
maintains its own shape and volume
almost no compressibility
almost no ability to flow
condensation
gas to liquid
exothermic
negative heat of vaporization
vaporization
liquid to gas
endothermic
heat of vaporization
freezing
liquid to solid
exothermic
negative heat of fusion
melting
solid to liquid
endothermic
heat of fusion
sublimation
solid to gas
exothermic
heat of sublimation
deposition
gas to solid
endothermic
negative heat of sublimation
standard enthalpy changes
heat of vaporization, fusion, sublimation
measured in kilojoules per mole
heating-cooling curve
a plot of temperature vs. time for a substance when heat is absorbed or released by the system at a constant rate
q =
m c deltaT
heat of vaporization is ____ than the heat of fusion
always greater
vapor pressure
the pressure exerted by a vapor at equilibrium with its liquid in a closed system
effect of temp on vapor pressure
higher temperature - higher pressure
effect of intermolecular forces on vapor pressure
weaker forces - higher pressure
clausius-slapeyron equation
ln (P2/P1) = (-heat of vap/R)(1/t2 - 1/t1)

R = 8.314 J/ mol K
boiling point
the temperature at which the vapor pressure equals the external pressure, usually that of the atmosphere
effect of pressure on boiling point
lower pressure = lower boiling point
melting point
the temperature at which the solid and liquid forms of a substance are at equilibrium
phase diagram
a diagram used to describe the stable phases and phase changes o a substance as a function of temperature and pressure
triple point
the pressure and temperature at which three phases of a substance are in equilibrium. In a phase diagram, the point at which three phase-transition curves meet
critical point
the point on a phase diagram above which the vapor cannot be condensed to a liquid, the end of the liquid-gas curve
van der Waals radius
one half of the shortest distance between the nuclei of identical nonbonding atoms. always larger than the covalent radiu
Ionic bonding
cation-anion
400-4000 kJ/mol
ex) NaCl
covalent
nuceir-shared e- pair
150 - 1000 kJ mol
ex) H-H
metallic
cations - delocalized electrons
75 - 1000 kJ/ mol
e) Fe
ion-dipole
ion charge - dipole charge
40-600 kJ/ mol
ex - NaOH2
H-bond
polar bond to H - dipole charge (high EN of N,O, and F)
10-40 kJ/mol
dipole-dipole
dipole charges
5-25 kJ/mol
ion-induced dipole
ion charge - polarizable e- cloud
3-15 kJ/mol
dipole-induced dipole
dipole charge - polarizable e- cloud
2-10 kJ/mol
dispersion (Londnon)
polarizable e- clouds
0.05-40 kJ/mol
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