CHEM 115 LATEST ACTUAL EXAM 2026/2027 QUESTIONS
AND SOLUTIONS RATED A+
✔✔what are atomic/molecular properties that can be computed by using computational
chemistry? - ✔✔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? - ✔✔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? - ✔✔1. type
of motion, 2. masses of the atoms, 3. strength of the bond
✔✔Intramolecular forces - ✔✔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 - ✔✔(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? -
✔✔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 - ✔✔one-half of the shortest distance between the nuclei of
identical nonbonded atoms.
✔✔ion-dipole forces - ✔✔the intermolecular attractive force between an ion and a polar
molecule (dipole)
✔✔dipole-dipole forces - ✔✔the intermolecular attraction between oppositely charged
poles of nearby polar molecules (469).
✔✔hydrogen bonding (H bond) - ✔✔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 - ✔✔the ease with which a particle's electron cloud can be distorted
(472).
✔✔dispersion (London) forces - ✔✔the intermolecular attraction between all particles as
a result of instantaneous polarizations of their electron clouds; the intermolecular force
primarily responsible for the condensed states of nonpolar substances.
✔✔What is the origin of a dipole in a polar molecule based on differences on
electronegativity of the bonded atoms? - ✔✔picture one atom in a sample of argon gas.
over time, its 18 electrons are distributed uniformly so that atom is nonpolar. but at any
instant there may be more electrons on one side of the nucleus than the other, which
gives the atom an instantaneous dipole.
✔✔What are the trends or polarizability - ✔✔1. it increases down a group because
atomic size increases and larger atomic clouds are easier to distort. 2. it decreases
across a period because increasing Z-eff makes the atoms smaller and holds the
electrons more tightly. 3. cations are less polarizable that their parent atoms because
they are smaller, anions are more polarizable because they are larger.
✔✔What factors influence the strength of dispersion (London) forces? - ✔✔1. depends
on the polarizability of the particles, so they are weak for small particles. polarizability
depends on the number of electrons which correlates closely with molar mass.
✔✔Lewis Structure - ✔✔a structural formula of electron-dot symbols, with lines as
bonding pairs and dots as lone pairs.
✔✔How do nuclear changes differ from chemical changes? - ✔✔in chemical reactions,
electrons are shared or transferred to form compounds, while nuclei remain unchanged.
while in nuclear reactions, nuclei undergo changes that form new elements and are
accompanied by energy changes that are a million times greater (therefore changes in
mass are detectable), and nuclear reactions are not subject to the effects of pressure,
temperature, and catalysis.
✔✔radioactivity - ✔✔the emissions resulting from the spontaneous disintegration of an
unstable nucleus (1053).
✔✔nucleon - ✔✔a subatomic particle found in the nucleus; a proton or a neutron.
✔✔nuclide - ✔✔a nuclear species with specified numbers of protons and neutrons.
✔✔isotopes - ✔✔atoms of a given atomic number (that is of a specific element) that
have different numbers of neutrons and therefore different mass numbers (54, 1054).
AND SOLUTIONS RATED A+
✔✔what are atomic/molecular properties that can be computed by using computational
chemistry? - ✔✔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? - ✔✔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? - ✔✔1. type
of motion, 2. masses of the atoms, 3. strength of the bond
✔✔Intramolecular forces - ✔✔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 - ✔✔(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? -
✔✔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 - ✔✔one-half of the shortest distance between the nuclei of
identical nonbonded atoms.
✔✔ion-dipole forces - ✔✔the intermolecular attractive force between an ion and a polar
molecule (dipole)
✔✔dipole-dipole forces - ✔✔the intermolecular attraction between oppositely charged
poles of nearby polar molecules (469).
✔✔hydrogen bonding (H bond) - ✔✔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 - ✔✔the ease with which a particle's electron cloud can be distorted
(472).
✔✔dispersion (London) forces - ✔✔the intermolecular attraction between all particles as
a result of instantaneous polarizations of their electron clouds; the intermolecular force
primarily responsible for the condensed states of nonpolar substances.
✔✔What is the origin of a dipole in a polar molecule based on differences on
electronegativity of the bonded atoms? - ✔✔picture one atom in a sample of argon gas.
over time, its 18 electrons are distributed uniformly so that atom is nonpolar. but at any
instant there may be more electrons on one side of the nucleus than the other, which
gives the atom an instantaneous dipole.
✔✔What are the trends or polarizability - ✔✔1. it increases down a group because
atomic size increases and larger atomic clouds are easier to distort. 2. it decreases
across a period because increasing Z-eff makes the atoms smaller and holds the
electrons more tightly. 3. cations are less polarizable that their parent atoms because
they are smaller, anions are more polarizable because they are larger.
✔✔What factors influence the strength of dispersion (London) forces? - ✔✔1. depends
on the polarizability of the particles, so they are weak for small particles. polarizability
depends on the number of electrons which correlates closely with molar mass.
✔✔Lewis Structure - ✔✔a structural formula of electron-dot symbols, with lines as
bonding pairs and dots as lone pairs.
✔✔How do nuclear changes differ from chemical changes? - ✔✔in chemical reactions,
electrons are shared or transferred to form compounds, while nuclei remain unchanged.
while in nuclear reactions, nuclei undergo changes that form new elements and are
accompanied by energy changes that are a million times greater (therefore changes in
mass are detectable), and nuclear reactions are not subject to the effects of pressure,
temperature, and catalysis.
✔✔radioactivity - ✔✔the emissions resulting from the spontaneous disintegration of an
unstable nucleus (1053).
✔✔nucleon - ✔✔a subatomic particle found in the nucleus; a proton or a neutron.
✔✔nuclide - ✔✔a nuclear species with specified numbers of protons and neutrons.
✔✔isotopes - ✔✔atoms of a given atomic number (that is of a specific element) that
have different numbers of neutrons and therefore different mass numbers (54, 1054).
