MSE 2001 test two (not mine)

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A series of similar metal alloys have the following enthalpies of fusion: Alloy A: 4 kJ / molAlloy B: 14 kJ / molAlloy C: 7 kJ/ molAlloy D: 20 kJ / molBased on this information, can you predictively rank these alloys from least stiff to most stiff? (Least Stiff) A < C < B < D (Most Stiff) (Least Stiff) A < B < C < D (Most Stiff) (Least Stiff) D < B < C < A (Most Stiff) It is NOT possible to make a reasonable prediction from the information provided.

(Least Stiff) A < C < B < D (Most Stiff)

The thermal energy of a single atom in a solid at room temperature (25°C) is approximately: 4.1x10-21 eV 0.0022 eV 3.45x10-22 eV 0.026 eV

0.026 eV

Rotational Symmetry plus translation which rotatiuonal symmetries when combined with translation can fill all of the 2d space

1-fold 2-fold 3-fold 4-fold 6-fold not 5 fold 8 fold

rectangle fold symmetry

2

rotoinversion

2 transformation rotation around 360/n immediately followed by an inversion at the center of symmetry

In what order do the following orbitals fill: 2s, 3p, 4s, 4p, 4f, 5p, 5d, 6s? 2s, 4s, 3p, 4p, 5p, 6s, 4f, 5d 2s, 3p, 4s, 4p, 5p, 6s, 4f, 5d 2s, 3p, 4s, 4p, 4f, 5p, 5d, 6s 2s, 3p, 4s, 4p, 5p, 4f, 6s, 5d 2s, 3p, 4s, 4p, 6s, 5p, 4f, 5d

2s, 3p, 4s, 4p, 5p, 6s, 4f, 5d

triangle fold symmetry

3

What electronic configuration would you expect for a ruthenium cation in a ceramic (ionic) solid? (Assume Ru is in its most stable oxidation state) 2+ charge with electronic configuration: [Kr]5s04d5 3+ charge with electronic configuration: [Kr]5s05d5 3+ charge with electronic configuration: [Kr]5s04d6 3+ charge with electronic configuration: [Kr]5s04d5 2+ charge with electronic configuration: [Kr]5s04d6 2+ charge with electronic configuration: [Kr]5s05d6

3+ charge with electronic configuration: [Kr]5s04d5

pentagon fold symmetry

4

square fold symmetry

4

hexagonal fold symmetry

6

octagonal fold symmetry

8

Which of the following polymers do you think may form hydrogen bonds? (Feel free to Google the polymer structures.) A. Poly(acrylic acid), PAA B. Nylon 6 C. Polytetrafluoroethylene (PTFE, or "Teflon") D. Polypropylene A & B A & C A, B, & C All of the above

A & B

What type(s) of bonding would you expect in the common refractory ceramic Al2O3? (Choose the BEST answer). A mixture of ionic and metallic bonding. Covalent bonding van der Waals bonding Metallic Bonding A mixture of covalent and van der Waals bonding. Ionic bonding A mixture of ionic and covalent bonding.

A mixture of ionic and covalent bonding.

What do electrons do in a solid? A. Form the bonds between atoms. Both B & C Both A & C A, B, and C C. Determine the fluorescent properties of a material. Both A & B B. Determine the magnetic properties of a material.

A, B, and C

Base centered

A,B,C

Which of these bond types is/are directional? A. Covalent Bonds B. Ionic Bonds C. Metallic Bonds D. London Dispersion Forces A & B A & D All of the above

A. Covalent Bonds

HCP

ABAB

FCC

ABCABC

If AX and BX are both predominantly ionic solids and AX has a higher melting temperature than BX, what else might you predict about the properties of AX and BX? AX will have a lower coefficient of thermal expansion because the bond-energy curve has a deeper and more narrow energy well than the BX bond-energy curve. AX will be stiffer because the bond-energy curve has a shallower and broader energy well than the BX bond-energy curve. BX will be stiffer because the bond-energy curve has a deeper and more narrow energy well than the AX bond-energy curve. AX will have a higher coefficient of thermal expansion because the bond-energy curve has a deeper and more narrow energy well than the BX bond-energy curve. BX will have a lower coefficient of thermal expansion because the bond-energy curve has a deeper and more narrow energy well than the AX bond-energy curve.

AX will have a lower coefficient of thermal expansion because the bond-energy curve has a deeper and more narrow energy well than the BX bond-energy curve. The higher melting temperature makes AX have a deeper energy well--this makes it have a lower CTE (and also higher stiffness).

GaAs is a common semiconductor used to make solid state lasers used in CD and DVD players. How covalent are the bonds in GaAs? About 13% covalent About 3% covalent. About 91% covalent. About 97% covalent. About 87% covalent. About 9% covalent

About 97% covalent.

What are materials made out of

Atoms

The space group I4/m has what type of Bravais lattice? Body centered Base centered Primitive Symmetric Face centered

Body centered

Electrons are the primary atomic species contributing to:

Bonding - crystal structure - mechanical properties electronic properties optical properties magnetic properties

Considering the ionic nature of the Mg-O and Na-Cl bonds, which of the following statements do you agree with? A. Mg-O likely forms a stronger bond than Na-Cl because it is made between divalent ions rather than monovalent ions. B. Mg-O is likely a double bond while Na-Cl is likely a single bond. C. Assuming bond distances are about equal, Mg-O will likely form a 4x stronger bond than Na-Cl. Both A & B are likely true. Both A & C are likely true. Both B & C are likely true. All are likely true.

Both A & C are likely true.

The curvature of the Energy-bond distance curve has a direct phenomenological relationship to: A. The elastic modulus of a material. B. The yield strength of a material. C. The toughness of a material. D. The stiffness of a material. Both A & B Both A & C Both A & D A, B, & C. A, B, & D. A, B, C, & D.

Both A & D

These types of bonds share electrons between atoms. A. Ionic bonds B. Covalent bonds C. Metallic bonds D. van der Waals Bonds Both A & B Both B & C Both B & D

Both B & C

Which of the following can be used to estimate the depth of the energy well for a bond? A. The principle quantum number B. The enthalpy of fission C. The enthalpy of fusion Both A & C None of these.

C. The enthalpy of fusion

Which of the following elements would you expect to have the highest electronegativity? Cl Co Ge Ba Si

Cl

Which type(s) of bonding would you expect to find in the solid semiconductor germanium? Ionic bonding only. A mixture of covalent and van der waals bonding. A mixture of ionic and covalent bonding. Metallic bonding only. Covalent bonding only. A mixture of covalent and metallic bonding. Van der Waals bonding only.

Covalent bonding only.

Symmetry

Crystalline solids are those in which the atomic arrangement repeats itself Because of this repetition, we can use symmetry to simplify our description of the atomic arrangement in a solid. For example, all of the atoms in a close-packed solid are symmetrically identical, and therefore they all have the same coordination number.

he microstructure of materials: Crystalline "Grains"

Each grain is a single crystal of a material oriented in some "arbitrary" direction. Polycrystalline materials are formed by multiple grains with different arbitrary orientations impinging upon one another.

If a crystal structure is found to have all of its lattice parameters equal to one another (a = b = c), which crystal class might it belong to? A. Cubic B. Tetragonal C. Hexagonal D. Rhombohedral Either A or B Either A or C Either A or D

Either A or D

Covalent bonds

Electron(s) in the valence shell are shared between atoms Bonding is a result of orbital-orbital overlap (between unfilled, valence orbitals) Polymers and semiconductors usually have covalent bonds. Generally "stronger" than ionic or metallic bonds

ionic bonds

Electron(s) are transferred between atoms, forming ions Bonding is a result of cation (+) attracting anion (-) (i.e.,Coulombic attraction) Oxide ceramics are typically considered ionic solids, (& carbides, nitrides, & sulfides)

face centered

F

Based solely on their electronic configurations, which of these metals would you expect to have the largest saturation magnetization? (Assume no electrons are transferred between orbitals.) Iron Vanadium Manganese Zinc Palladium

Manganese

The intermetallic Al3Ni will PRIMARILY exhibit what type of bonding? Metallic "James Bond"ing Ionic Covalent van der Waals Hydrogen

Metallic

Inter axial angle

Physical angle between the three primary axes

Lattice parametr or lattice constant

Physical length of the side of unit cell (denoted here as: a, b, & c). These lengths are usually in angstroms or nanometers.

which orbital does most of the bonding in ionic solids plus metals

S orbitals

Why are ionic solids like most ceramics brittle? The need for bond directionality leads to fracture when the material is plastically deformed. Van der Waals bonds must be present to have non-brittle behavior. The non-directionality of bonding in ionic solids leads to fracture upon plastic deformation. The alignment of similarly charged ions upon plastic deformation leads to fracture.

The alignment of similarly charged ions upon plastic deformation leads to fracture.

grain boundaries

The boundaries between these misoriented single crystal grains are NOT well ordered

Coordination Number

The most basic descriptor for the arrangement of atoms in a solid is the "coordination number" of each atom. This is thenumber of nearest neighbor atoms surrounding a given atom.

microstructure

The size and relative orientation of grains

Unit cell

The smallest, repeatable unit that when translated in 3 chosen directions can cover all of space. This repeating pattern of unit cells forms the crystalline structure of a material.

Thermal energy of atoms in a system

Thermal energy of an atom KbT all atoms at T greater than 0 kelvin have non-zero energy this energy manifest mostly as atomic vibrations

Metallic bonds

Valence shell electron(s) are delocalized and shared across the ENTIRE solid. Bonding is a result of the atomic cores (nuclei + inner shells) "floating" in a " jellium" of valence electrons (also called: "electron sea" or "electron gas") Metals have metallic bonding (duh!)

Close-Packing: The Crystal Structure of (Many) Metals

We will start by studying the crystal structure of metals because they are the "simplest" to understand, a prototypical system, and have broad importance in engineering design. All solids desire an atomic packing arrangement that minimizes the total energy of the system Because metallic bonding is non-directional and all atoms are the same, metal atoms want to pack to maximize space filling a missing atom would reduce the average number of electrons in the electron sea and around neighboring atoms. These atoms would then be less satisfied and in a higher energy state

van der waals bonding

Weak attractions between atoms due to the polarity of other bonds (dipoles) AKA London Dispersion Forces, dipole-dipole bonding, hydrogen bonding, etc Dipole can be instantaneous (very, very weak) or permanent (a little stronger, e.g. H-bonds)

What is the expected electronic configuration of elemental (non-ionized) copper? [Ar] 4s23d9 [Kr] 4s13d10 [Ar] 4s13d10 [K] 4s23d9 [Ar] 4s13d10

[Ar] 4s13d10

Hexagonal

a=b/c A=B=90 Y=120 Primitive(P) ZuO CdS

Cubic

a=b=c A=B=Y=90 Primitive(P) body Centered(I) face Centered(F) NaCl Cu

Rhombohedral

a=b=c ; a=b=y /=90 Primitive(P) CaCO3

Crystal symmetry

all have some form of rotational symmetry This rotational symmetry must be concomitant with the ability to spatially translate and fill all space

Identity

all objects have identity, even the most assymmetric object have at least 1 symmetry

Bonding & Coefficient of Thermal Expansion (CTE)

assymetry of the atomic bonding potential energy well leads to a larger CTE rule of thumb: deeper potential energy wells are usually more symmetric and have lower CTEs increases change heat fusion decrease CTE

What determines the density of a material

atomic mass f the elements that make up the material --> composition how well the atoms pack into the solid --> crystal structure void space or porosity--> defects

Density

atoms actually contain a lot of empty space the nucleus contains most of the mass but it is only a small fraction an atoms' entire volume For example, while francium has an atomic weight that is 32x higher than lithium the difference in atomic size between francium and lithium is only about 2x therefore atomic mass is the primary factor in determining the density of a fully dense solid no porosity particularly in metals Crystal structure becomes more important for covalent and ionic bonded crystals, where the directionality of bonding forces more open structures

What happens if we plastically deform a metal?

atoms/bonds look the same sliding atoms by 1 atomic position does not change the bonding state

Rotational Symmetry

axis of rotation

Orthorhombic

a≠b≠c α=β=γ=90 Primitive(P) body Centered(I) Base Centered(C) face Centered(F) BaSO4 KNO3

Monoclinic

a≠b≠c α=γ=90° β≠90° Primitive(P) body Centered(I) Cimabar monoclinic

Triclinic

a≠b≠c α≠β≠γ Primitive(P) K2cr2O7

covalent bonds and directionality

covalent bonds are directional bonding requires maximizing orbital overlap therefore orbital shape is important

Tetragonal

crystal system: a = b ≠ c; α = β = γ = 90° Primitive(P) body Centered(I) TiO3

Because van der Waals bonding is about 100x weaker than other types of bonding (e.g., ionic, covalent, metallic), it has no influence on the properties of a material. true false

false

Positively charged ions are called anions. true or false

false

Simply shining infrared light onto an elemental metal can cause electron emission. True or false

false Infrared light is not of high enough energy to emit electrons from the bonding well in metals. Light in the UV range is of the appropriate energy, occasionally blue or purple visible light is sufficient.

Primitive(P)

forms of these crystals have lattice points("atoms") only at the corners

elastic modulus (E)

how much force is required to displace an atom from its equilibrium position higher slope = stiffer material smaller radius = greater curvature = greater stiffness

Body centered

i

Thermodynamics & Kinetics

if we know the barrier energy for this task, then we can compare this energy to the thermal energy of the atoms in the system. If thermal energy greater than barrier energy then the task is likely to happen

ionic bonding and directionality

ionic bonding is non-directional some bond energy regardless of orientation between two atoms

Lattice

is a regular collection of points in euclidean space

crystal structure

lattice plus basis

Mirror Symmetry

line symmertiy

What are the d-shells and f-shells good for

magnetism - d plus f orbitals are separate from bonding so they can act independently lots of unpaired electrons creates high spin - good saturation polarization, permanence Fluorescence + phosphorescence - crystal structures of a material can lead to induce orbitals in d or f shells to have different energies

Theoretical Density

mass of atoms in unit cell Multiply mass by number of atoms)/volume of unit cell

Metallic Bonds and directionality

metallic bonds are non directional most metals have s-orbitals as their valence shell--> spherical--> non directional symmetry

which orbital does most of the bonding in covalent solids

mix of s and p orbitals

covalent solid

more complex, "open", structures determined by fixed bonding angles

"Short Range Order" (SRO)

nearly all materials have SRO coordination number is a form

"Long Range Order" (LRO)

occurs in crystalline materials. LRO requires that each of the SRO units repeat their arrangement in 3-dimensional space.

Why is it ok for covalent bonds to have some orbital overlap

orbitals are not completely filled

Valence shell

outermost electronic shell determines the bonding

What types of orbitals exist in the n = 2 shell? (Choose ALL that apply) p-orbitals g-orbitals s-orbitals f-orbitals d-orbitals

p-orbitals s-orbitals

ionic solid

packing of spheres to maximization space filling(efficient packing)

ionic bonding and fracture

repulsion leds to fracture why most ceramics are brittle

basis

set of atoms for the crystal cructure

Space Group

set of symmetry elements which completely describe the spatial arraghement of a 3d periodic pattern

Bravais Lattices

showing lattice points not actual atoms

Which material has a higher elastic modulus

steeper slope, less room to stretch at a finite temperature

What does the principle quantum number(n) tells us

the electrons distance from the nuclues

What happens when we heat up a gas

the gas molecules move faster, gain more energy, increase velocity, increase KE

center of inversion

there is always a matching part, which has the same distance from a central point but in opposite direction

core shells

these electrons are usually not involved in bonding

unit cell

translational symmetry smallest posrtion of the atomic arrangement which, if repeated in 3 dimensions, will form the entire atomic arragment of the solid

Why do polymers have such low elastic moduli?

van der waals holding chains together

hydrogen Bonding

very electronegative element which monopolizing the electrons


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