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Michigan State University
CEM 141 CEM 141 Exam 3 Questions and
Answers 2026 Latest Update
Differentiate between properties of atoms, nano-particles, and larger
macroscale materials. Explain why is it that atoms don't have macroscopic
properties like melting point, boiling point, and color, while macroscopic
materials do (and can be identified by them). Ans: The properties of new
substances depend on its molecular structure - the properties are emergent
For molecules to melt they interact with other molecules. It would not be
possible to melt a single atom/molecule.
Explain the force and energy changes that occur when two atoms approach
each other and form a bond. Explain why a third body (another atom or
molecule) is (almost always) needed to form a stable bond. (Think back to
what we learned in Chapter 1. Ans: A third atom will absorb some of the
energy thus lowering the energy between to atoms allowing the two atoms
to form a stable bond.
What determines whether a bond or interaction is stable? Explain how
temperature influences the stability of bonds and interactions Ans: The
stability of atoms depends on whether or not their outer-most shell is filled
with electrons. If the outer shell is filled, the atom is stable.
If you put enough energy (heat/temperature) in, the bond will break and the
atoms connected by that bond will fly apart.
Compare and contrast the molecular orbital bond model and the valence
bond model. What are the similarities? What are the differences Ans: ...
Valence Bond Theory Ans: two orbitals combine to form a bond between
two atoms
© 2026 All rights reserved
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a single pair of electrons can be shared only by two, bonded atoms in the
molecule
focuses on bonding interactions
uses hybridization to explain geometry of molecules
Molecular Orbital Theory Ans: Orbitals from each atom in the molecule can
combine to form molecular orbitals
a single pair of electrons can be spread across numerous atoms in the
molecule
atomic orbital interactions produce both bonding and antibonding orbitals
uses symmetry of atomic orbitals to explain geometry of molecules
Describe the bonding in diamond and graphite in terms of the hybrid orbital
model (valence bond theory). Ans: In order to create covalent bonds in
diamond, the s orbital mixes with the three p orbitals to form sp3
hybridization. The four valence electrons are thus equally distributed
among the sp3 orbitals, while each orbital points to one of the four corners
of a tetrahedron. The tetrahedral structure, together with the highly directed
charge density, give strength and stability to the bonds.
Explain how the macroscopic properties of diamond and graphite
(appearance, melting point, strength, electricity conductance, etc.) can be
explained in terms of the kind of bonding that occurs in these networks
Ans: The model of bonding in diamond uses the idea that electrons are
localized between the two nuclei that participate in the bond. The electrons
cannot move out of this area and therefore are not mobile (as they are in
metals). To conduct electricity electrons must be able to move freely in
molecular orbitals that extend throughout the whole structure
To melt diamond, the strong C-C covalent bonds must be broken, since the
structure is a 3D network of these bonds. Substances that exist as molecules
tend to have lower melting points because it is the intermolecular forces
between the molecules that are overcome rather than the actual covalent
bonds.
© 2026 All rights reserved
Michigan State University
CEM 141 CEM 141 Exam 3 Questions and
Answers 2026 Latest Update
Differentiate between properties of atoms, nano-particles, and larger
macroscale materials. Explain why is it that atoms don't have macroscopic
properties like melting point, boiling point, and color, while macroscopic
materials do (and can be identified by them). Ans: The properties of new
substances depend on its molecular structure - the properties are emergent
For molecules to melt they interact with other molecules. It would not be
possible to melt a single atom/molecule.
Explain the force and energy changes that occur when two atoms approach
each other and form a bond. Explain why a third body (another atom or
molecule) is (almost always) needed to form a stable bond. (Think back to
what we learned in Chapter 1. Ans: A third atom will absorb some of the
energy thus lowering the energy between to atoms allowing the two atoms
to form a stable bond.
What determines whether a bond or interaction is stable? Explain how
temperature influences the stability of bonds and interactions Ans: The
stability of atoms depends on whether or not their outer-most shell is filled
with electrons. If the outer shell is filled, the atom is stable.
If you put enough energy (heat/temperature) in, the bond will break and the
atoms connected by that bond will fly apart.
Compare and contrast the molecular orbital bond model and the valence
bond model. What are the similarities? What are the differences Ans: ...
Valence Bond Theory Ans: two orbitals combine to form a bond between
two atoms
© 2026 All rights reserved
, 2 | Page
a single pair of electrons can be shared only by two, bonded atoms in the
molecule
focuses on bonding interactions
uses hybridization to explain geometry of molecules
Molecular Orbital Theory Ans: Orbitals from each atom in the molecule can
combine to form molecular orbitals
a single pair of electrons can be spread across numerous atoms in the
molecule
atomic orbital interactions produce both bonding and antibonding orbitals
uses symmetry of atomic orbitals to explain geometry of molecules
Describe the bonding in diamond and graphite in terms of the hybrid orbital
model (valence bond theory). Ans: In order to create covalent bonds in
diamond, the s orbital mixes with the three p orbitals to form sp3
hybridization. The four valence electrons are thus equally distributed
among the sp3 orbitals, while each orbital points to one of the four corners
of a tetrahedron. The tetrahedral structure, together with the highly directed
charge density, give strength and stability to the bonds.
Explain how the macroscopic properties of diamond and graphite
(appearance, melting point, strength, electricity conductance, etc.) can be
explained in terms of the kind of bonding that occurs in these networks
Ans: The model of bonding in diamond uses the idea that electrons are
localized between the two nuclei that participate in the bond. The electrons
cannot move out of this area and therefore are not mobile (as they are in
metals). To conduct electricity electrons must be able to move freely in
molecular orbitals that extend throughout the whole structure
To melt diamond, the strong C-C covalent bonds must be broken, since the
structure is a 3D network of these bonds. Substances that exist as molecules
tend to have lower melting points because it is the intermolecular forces
between the molecules that are overcome rather than the actual covalent
bonds.
© 2026 All rights reserved
