Materials Science and Engineering Final
Exam Review With 100% Correct
Answers
What is a crystalline solid? - correct answers ✔✔Crystalline solids are atoms, ions, or molecules
that make up a solid in a regular, well-defined arrangement.
What is a Unit Cell? - correct answers ✔✔The smallest repeating pattern of crystalline solids
(Unit cells are like bricks in a wall—they are all identical and repeating)
There are 4 types of Crystalline solids, what are they? - correct answers ✔✔Ionic Solids
Molecular Solids
Covalent Solids
Metallic Solids.
Ionic Solids - correct answers ✔✔Positive and negative ions and held together by electrostatic
attractions.
Very high melting points
brittleness
poor conductors
(An example of an ionic solid is table salt, NaCl)
Molecular Solids - correct answers ✔✔Atoms or molecules held together by London dispersion
forces, dipole-dipole forces, or hydrogen bonds.
,-low melting points
-flexibility
-poor conductors
(Example: Ice)
Covalent-network (also called atomic) solids - correct answers ✔✔Atoms connected by covalent
bonds; the intermolecular forces are covalent bonds as well.
Very hard
Very high melting points
Poor conductors
(Examples of this type of solid are diamond)
Metallic Solids - correct answers ✔✔Metal atoms that are held together by metallic bonds
-high melting points
-ranges from soft(malleable) to very hard
-good conductors of electricity
(Ex: Gold)
BBC (Body Centered Cubic) - correct answers ✔✔a unit cell with an atomic packing
arrangement in which one atom is in contact with 8 identical atoms located at the corners of an
imaginary cube
,FCC (Face Centered Cubic) - correct answers ✔✔a unit cell with atomic packing where each
atom has 12 nearest neighbors, the stacking sequence of close-packed layers is ABCABCABCABC
APF (Atomic Packing Factor) - correct answers ✔✔the volume of atoms in a selected unit cell
divided by the volume of the unit cell
Point Defects - correct answers ✔✔vacancies and self interstitials
Vacancies - correct answers ✔✔The simplest of the point defects is a vacancy, or vacant lattice
site, one normally occupied
but from which an atom is missing. All crystalline solids contain
vacancies, and, in fact, it is not possible to create such a material that is free of these defects.
The necessity of the existence of vacancies is explained using principles of
thermodynamics; in essence, the presence of vacancies increases the entropy (i.e., the
randomness) of the crystal.
Self-Interstitials - correct answers ✔✔A self-interstitial is an atom from the crystal that is
crowded into an interstitial site—a small void space that under ordinary circumstances is not
occupied. In metals, a self-interstitial introduces relatively large distortions in the surrounding
lattice because the atom is substantially larger than the interstitial position in which it is
situated. Consequently, the formation of this defect is not highly probable, and it exists in very
small concentrations that are significantly lower than for vacancies.
FCC Edge Length - correct answers ✔✔a = 2R(sqrt(2))
FCC Coordination Number - correct answers ✔✔12
FCC Atoms Per cell - correct answers ✔✔4
, BCC Edge Length - correct answers ✔✔4R/(sqrt(3))
BCC Coordination Number - correct answers ✔✔8
BCC Atoms Per Cell - correct answers ✔✔2
Alloy - correct answers ✔✔a metallic substance that is composed of two or more elements
Solid Solution - correct answers ✔✔the result from the addition of impurity atoms to a metal as
well as the formation of a new second phase depending on
(1) the kinds of impurity
(2) their concentrations
(3) the temperature of the alloy
(4) Both substitutional and interstitial versions of this are possible.
Substitutional Solid Solution - correct answers ✔✔a solid solution where in the solute atoms
replace or substitute for the host atoms
Interstitial Solid Solution - correct answers ✔✔A solid solution wherein relatively small solute
atoms occupy interstitial positions between the solvent or host atoms.
Solute and solvent - correct answers ✔✔Solute: One component or element of a solution
present in a minor concentration. It is dissolved in the solvent
Solvent: The component of a solution present in the greatest amount. It is the component that
dissolves a solute.
Exam Review With 100% Correct
Answers
What is a crystalline solid? - correct answers ✔✔Crystalline solids are atoms, ions, or molecules
that make up a solid in a regular, well-defined arrangement.
What is a Unit Cell? - correct answers ✔✔The smallest repeating pattern of crystalline solids
(Unit cells are like bricks in a wall—they are all identical and repeating)
There are 4 types of Crystalline solids, what are they? - correct answers ✔✔Ionic Solids
Molecular Solids
Covalent Solids
Metallic Solids.
Ionic Solids - correct answers ✔✔Positive and negative ions and held together by electrostatic
attractions.
Very high melting points
brittleness
poor conductors
(An example of an ionic solid is table salt, NaCl)
Molecular Solids - correct answers ✔✔Atoms or molecules held together by London dispersion
forces, dipole-dipole forces, or hydrogen bonds.
,-low melting points
-flexibility
-poor conductors
(Example: Ice)
Covalent-network (also called atomic) solids - correct answers ✔✔Atoms connected by covalent
bonds; the intermolecular forces are covalent bonds as well.
Very hard
Very high melting points
Poor conductors
(Examples of this type of solid are diamond)
Metallic Solids - correct answers ✔✔Metal atoms that are held together by metallic bonds
-high melting points
-ranges from soft(malleable) to very hard
-good conductors of electricity
(Ex: Gold)
BBC (Body Centered Cubic) - correct answers ✔✔a unit cell with an atomic packing
arrangement in which one atom is in contact with 8 identical atoms located at the corners of an
imaginary cube
,FCC (Face Centered Cubic) - correct answers ✔✔a unit cell with atomic packing where each
atom has 12 nearest neighbors, the stacking sequence of close-packed layers is ABCABCABCABC
APF (Atomic Packing Factor) - correct answers ✔✔the volume of atoms in a selected unit cell
divided by the volume of the unit cell
Point Defects - correct answers ✔✔vacancies and self interstitials
Vacancies - correct answers ✔✔The simplest of the point defects is a vacancy, or vacant lattice
site, one normally occupied
but from which an atom is missing. All crystalline solids contain
vacancies, and, in fact, it is not possible to create such a material that is free of these defects.
The necessity of the existence of vacancies is explained using principles of
thermodynamics; in essence, the presence of vacancies increases the entropy (i.e., the
randomness) of the crystal.
Self-Interstitials - correct answers ✔✔A self-interstitial is an atom from the crystal that is
crowded into an interstitial site—a small void space that under ordinary circumstances is not
occupied. In metals, a self-interstitial introduces relatively large distortions in the surrounding
lattice because the atom is substantially larger than the interstitial position in which it is
situated. Consequently, the formation of this defect is not highly probable, and it exists in very
small concentrations that are significantly lower than for vacancies.
FCC Edge Length - correct answers ✔✔a = 2R(sqrt(2))
FCC Coordination Number - correct answers ✔✔12
FCC Atoms Per cell - correct answers ✔✔4
, BCC Edge Length - correct answers ✔✔4R/(sqrt(3))
BCC Coordination Number - correct answers ✔✔8
BCC Atoms Per Cell - correct answers ✔✔2
Alloy - correct answers ✔✔a metallic substance that is composed of two or more elements
Solid Solution - correct answers ✔✔the result from the addition of impurity atoms to a metal as
well as the formation of a new second phase depending on
(1) the kinds of impurity
(2) their concentrations
(3) the temperature of the alloy
(4) Both substitutional and interstitial versions of this are possible.
Substitutional Solid Solution - correct answers ✔✔a solid solution where in the solute atoms
replace or substitute for the host atoms
Interstitial Solid Solution - correct answers ✔✔A solid solution wherein relatively small solute
atoms occupy interstitial positions between the solvent or host atoms.
Solute and solvent - correct answers ✔✔Solute: One component or element of a solution
present in a minor concentration. It is dissolved in the solvent
Solvent: The component of a solution present in the greatest amount. It is the component that
dissolves a solute.
