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

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

trigonal planar, 120

tetrahedral, 109.5

trigonal bipyramidal, 90, 120

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

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

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

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.

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

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

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

B2, C2, N2
sgma2p, pi2p, pi2p, sigma2p

unpaired electrons

all paired electrons

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

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

a physical change from one phase to another, usually referring to a change in physical state

the electrostatic potential energy depends on the charges of the particles and the distances between them

conforms to the shape and volume of a container
high compressibility
high ability to flow

conforms to the shape of container, volume limited by surface
very low compressibility
moderate ability to flow

maintains its own shape and volume
almost no compressibility
almost no ability to flow

gas to liquid
exothermic
negative heat of vaporization

liquid to gas
endothermic
heat of vaporization

liquid to solid
exothermic
negative heat of fusion

solid to liquid
endothermic
heat of fusion

solid to gas
exothermic
heat of sublimation

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

heat of vaporization is ____ than the heat of fusion

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

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

the temperature at which the solid and liquid forms of a substance are at equilibrium

a diagram used to describe the stable phases and phase changes o a substance as a function of temperature and pressure

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

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

cation-anion
400-4000 kJ/mol
ex) NaCl

nuceir-shared e- pair
150 - 1000 kJ mol
ex) H-H

cations - delocalized electrons
75 - 1000 kJ/ mol
e) Fe

ion charge - dipole charge
40-600 kJ/ mol
ex - NaOH2

polar bond to H - dipole charge (high EN of N,O, and F)
10-40 kJ/mol

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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