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Michigan State University
CEM 141 Chemistry Exam #3 Questions and
Answers 2026 Latest Update
Predict, draw models (pictures), and explain why relative melting points and
boiling points for substances that exist as molecules (like H2) differ from
those that exist as continuous extended networks (like diamond or metals.
Ans: When molecules are melted or boil, only LDFs (or dipole-dipole/H-bond
interactions) need to be broken. These are relatively weak in comparison to
those in extended networks. To melt or boil something in a covalent
network, covalent bonds must be broken. For metals, the atoms exist in a
sea of shared valence electrons, and the atoms must be separated in order
to melt or boil the substance, which requires overcoming very strong
attractive electrostatic forces. As a result, it takes a much higher amount of
energy in order to melt or boil substances that exist in extended networks.
Explain why rotation is (generally) easy around a sigma (single) bond, but
more difficult around pi bonds. Ans: In sigma bonds, the orbitals overlap
end to end along the same axis, which allows for fairly easy rotation. In pi
bonds, the p orbitals overlap both above and below a horizontal axis, so
rotation would break the bond and therefore is not possible.
Use Lewis structures to deduce the hybridization of the atoms in a molecule.
Ans: Hybridization depends on the number of electron centers around the
central molecule. 2 yields sp hybridization, 3 yields sp2 hybridization, and 4
yields sp3 hybridization.
Predict the polarity of bonds using atom electronegativity. Predict the
polarity of molecules using bond polarity and molecular shape. Ans: When
the atoms in the bond have different electronegativity, the bond has the
potential to be polar depending on the arrangement of the atoms. The level
of polarity depends on the differences in electronegativity of the atoms
(greater difference means the bond is more polar).
hydrogen has electronegativity similar to that of carbon
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Use molecular structure and the polarity of a molecule to predict the type(s)
of intermolecular forces (London dispersion forces, dipole-dipole
interactions, and hydrogen bonding interactions) present in molecules. Ans:
LDFs: present in all atoms and molecules
Dipole-dipole interactions: present between polar molecules
Hydrogen bonding interactions: present when one molecule has a hydrogen
bonded to an O, N, or F and another molecule has an O, N, or F with a lone
pair (O, N, and F are highly electronegative).
Use intermolecular forces to explain properties of molecular compounds.
Predict and/or rank relative melting and boiling points of given compounds.
Ans: The stronger the IMF, the higher the relative melting or boiling point.
IMF strength depends on they type of IMF (LDF is weakest, H bond is
strongest), as well as the relative strength of that type of IMF. For example,
the more polar the molecules are in a dipole-dipole interaction, the stronger
it is. The more H bonds a molecule can form, the stronger it is.
Explain the difference between covalent bonding and ionic bonding using
the idea that there is a continuum of bonding ranging from pure covalent to
more or less ionic. Ans: Covalent bonds form between two nonmetals. Both
have relatively high electronegativity, and there are valence electrons which
are fought over between the two atoms in the bond. With ionic bonding, a
metal and a nonmetal are involved. The metal gives 1 to 3 valence electrons
to the nonmetal, forming two ions.
Explain why metals tend to form positive ions and non-metals tend to form
negative ions. Predict the charge on common single-atom ions. Ans: Metals
have low electronegativity meanign they are on the left side of the periodic
table. The metals are also more likely to give up electrons while non-metals
will take electrons. The metals and non-metals (which are more
electronegative and on the right side of the periodic table) want to achieve
noble gas status and the charge depends on the amount of transfered
electons.
Describe the structure of ionic compounds. Use the structure to explain the
properties of ionic compounds (for example, melting point, boiling point,
hardness, and ability to conduct electricity). Predict and/or rank relative
melting and boiling points of given compounds. Ans: Ionic compounds form
© 2026 All rights reserved
Michigan State University
CEM 141 Chemistry Exam #3 Questions and
Answers 2026 Latest Update
Predict, draw models (pictures), and explain why relative melting points and
boiling points for substances that exist as molecules (like H2) differ from
those that exist as continuous extended networks (like diamond or metals.
Ans: When molecules are melted or boil, only LDFs (or dipole-dipole/H-bond
interactions) need to be broken. These are relatively weak in comparison to
those in extended networks. To melt or boil something in a covalent
network, covalent bonds must be broken. For metals, the atoms exist in a
sea of shared valence electrons, and the atoms must be separated in order
to melt or boil the substance, which requires overcoming very strong
attractive electrostatic forces. As a result, it takes a much higher amount of
energy in order to melt or boil substances that exist in extended networks.
Explain why rotation is (generally) easy around a sigma (single) bond, but
more difficult around pi bonds. Ans: In sigma bonds, the orbitals overlap
end to end along the same axis, which allows for fairly easy rotation. In pi
bonds, the p orbitals overlap both above and below a horizontal axis, so
rotation would break the bond and therefore is not possible.
Use Lewis structures to deduce the hybridization of the atoms in a molecule.
Ans: Hybridization depends on the number of electron centers around the
central molecule. 2 yields sp hybridization, 3 yields sp2 hybridization, and 4
yields sp3 hybridization.
Predict the polarity of bonds using atom electronegativity. Predict the
polarity of molecules using bond polarity and molecular shape. Ans: When
the atoms in the bond have different electronegativity, the bond has the
potential to be polar depending on the arrangement of the atoms. The level
of polarity depends on the differences in electronegativity of the atoms
(greater difference means the bond is more polar).
hydrogen has electronegativity similar to that of carbon
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Use molecular structure and the polarity of a molecule to predict the type(s)
of intermolecular forces (London dispersion forces, dipole-dipole
interactions, and hydrogen bonding interactions) present in molecules. Ans:
LDFs: present in all atoms and molecules
Dipole-dipole interactions: present between polar molecules
Hydrogen bonding interactions: present when one molecule has a hydrogen
bonded to an O, N, or F and another molecule has an O, N, or F with a lone
pair (O, N, and F are highly electronegative).
Use intermolecular forces to explain properties of molecular compounds.
Predict and/or rank relative melting and boiling points of given compounds.
Ans: The stronger the IMF, the higher the relative melting or boiling point.
IMF strength depends on they type of IMF (LDF is weakest, H bond is
strongest), as well as the relative strength of that type of IMF. For example,
the more polar the molecules are in a dipole-dipole interaction, the stronger
it is. The more H bonds a molecule can form, the stronger it is.
Explain the difference between covalent bonding and ionic bonding using
the idea that there is a continuum of bonding ranging from pure covalent to
more or less ionic. Ans: Covalent bonds form between two nonmetals. Both
have relatively high electronegativity, and there are valence electrons which
are fought over between the two atoms in the bond. With ionic bonding, a
metal and a nonmetal are involved. The metal gives 1 to 3 valence electrons
to the nonmetal, forming two ions.
Explain why metals tend to form positive ions and non-metals tend to form
negative ions. Predict the charge on common single-atom ions. Ans: Metals
have low electronegativity meanign they are on the left side of the periodic
table. The metals are also more likely to give up electrons while non-metals
will take electrons. The metals and non-metals (which are more
electronegative and on the right side of the periodic table) want to achieve
noble gas status and the charge depends on the amount of transfered
electons.
Describe the structure of ionic compounds. Use the structure to explain the
properties of ionic compounds (for example, melting point, boiling point,
hardness, and ability to conduct electricity). Predict and/or rank relative
melting and boiling points of given compounds. Ans: Ionic compounds form
© 2026 All rights reserved
