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Purdue Chem 115 - Final Exam questions well answered
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Purdue Chem 115 - Final Exam questions well answered
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Purdue Chem 115 - Final ExamValence Bond Theory - correct answer ✔✔A model that attempts to reconcile the shapes of molecules
with those of atomic orbitals through the concepts of orbital overlap and hybridization (429).
hybridization - correct answer ✔✔a postulated process of orbital mixing to form hybrid orbitals (430).
hybrid orbitals - correct answer ✔✔an atomic orbital postulated to form during binding by the
mathematical mixing of specific combinations of nonequivalent orbitals on a given atom (430).
sp hybrid orbital - correct answer ✔✔an orbital formed by the mixing of one s and one p orbital of a
central atom (430).
sp2 hybrid orbital - correct answer ✔✔an orbital formed by the mixing of one s and two p orbitals of a
central atom (432).
sp3 hybrid orbital - correct answer ✔✔an orbital formed by the mixing of one s and three p orbitals of a
central atom (432).
sp3d hybrid orbitals - correct answer ✔✔an orbital formed by the mixing of one s, three p, and one d
orbital of a central atom (433).
sp3d2 hybrid orbital - correct answer ✔✔an orbital formed by the mixing of one s, three p, and two d
orbitals of a central atom (434).
How to determine hybrid orbitals from molecular formula - correct answer ✔✔1. take molecular
formula, 2. create lewis structure, 3. determine molecular shape and electron group arrangement, 4.
determine hybrid orbitals (434) - two helpful charts at bottom of page.
sigma bond - correct answer ✔✔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 (437).
,pi bond - correct answer ✔✔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 (437).
What are the major principles of the Valence Bond theory? - correct answer ✔✔1. a covalent bond
forms when orbitals of two atoms overlap and a pair of electrons occupy that overlap region. 2. there
are opposing spins of the electron pair. 3. there is a max. overlap of bonding orbitals (greater overlap =
closer nuclei to electrons/stronger bond)
What are features of hybrid orbitals? - correct answer ✔✔1. the number of orbitals equals the number
of atomic orbitals mixed, 2. the type of orbitals varies, 3. the shape and orientation of a hybrid orbital
maximizes its overlap with the orbital of the other atom in the bond.
Why is rotation about the bond axis restricted in molecules containing a pi bond? (i.e. either a
double/triple bond) - correct answer ✔✔a pi bond restricts rotation because the p orbitals must be
parallel to each other to overlap most effectively.
What are the main differences between molecular mechanics, semi-empirical and Ab Initio
computational models? - correct answer ✔✔1. Molecular mechanics is used when a molecule is too big
to effectively use the semi-empirical method. 2. Semi-empirical calculations can be done much faster
than Ab Initio calculations, but results can be erratic. 3. Ab Initio gives very good qualitative results and
they grow more accurate as size of molecule decreases.
What are the major benefits/goals of computational chemistry? - correct answer ✔✔1. Computational
chemistry tools can be used to investigate a much wider variety of chemical species than are normally
accessible to the experimental chemist. 2. is also allows chemists to think more clearly about issues that
are really central to chemistry - structure, stability, and reactivity - than would be possible without the
use of a computer. 3. goals are to eliminate/reduce time consuming experiments, provide insight into
existing experimental data, or guide new experimental studies.
what are atomic/molecular properties that can be computed by using computational chemistry? -
correct answer ✔✔1. molecular structures (both stable/unstable species) 2. heats of formation/reaction.
3. dipole moments. 4. ionization potentials. 5. charge and spin densities. 6. reaction mechanisms. 7.
activation energies. 8. vibrational modes.
, describe the considerations for choosing a computational model? - correct answer ✔✔1. need to
understand how the computational models are implemented and the nature of the databases used to
parameterize the models. 2. use this knowledge to determine the most appropriate model for a specific
investigation (i.e. the problem at hand) and to define the level of confidence required in the results. 3.
evaluate available computational resources and relative computational cost.
What factors determine the vibrational frequency for a covalent bond? - correct answer ✔✔1. type of
motion, 2. masses of the atoms, 3. strength of the bond
Intramolecular forces - correct answer ✔✔forces that are due to the attraction between cations and
anions (ionic bonding), nuclei and electron pairs (covalent bonding), or metal cations and delocalized
ions (metallic bonding).
intermolecular forces - correct answer ✔✔(nonbonding forces) arise from the attraction between
molecules with partial charges of between ions and molecules. (also called van der Waals forces).
What are differences between intramolecular and intermolecular forces? - correct answer ✔✔bonding
forces (intramolecular) are relatively strong because larger charges are closer together. Intermolecular
forces are relatively weak because smaller charges are farther apart.
van der Waals radius - correct answer ✔✔one-half of the shortest distance between the nuclei of
identical nonbonded atoms.
ion-dipole forces - correct answer ✔✔the intermolecular attractive force between an ion and a polar
molecule (dipole)
dipole-dipole forces - correct answer ✔✔the intermolecular attraction between oppositely charged
poles of nearby polar molecules (469).
hydrogen bonding (H bond) - correct answer ✔✔a type of dipole-dipole force that arises between
molecules that have an H atom bonded to a small, highly electronegative atom with lone pairs, usually N,
O, or F.
polarizability - correct answer ✔✔the ease with which a particle's electron cloud can be distorted (472).
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