EGN3365

Thermal conductivity of metals decreases with increasing ________

impurity content

properties fall into 6 categories

mechanical, electrical, thermal, magnetic, optical, deteriorative

covalent bond

pair of electrons shared between atoms in a molecule

ionic bond

bond resulting from the attraction between oppositely charged ions

metallic bond

attraction between positively charged metal ions and the electrons around them

primary bonding

ionic covalent metallic

secondary bonding

van der Waals hydrogen bonding

Some elements are stable because their ________ shell is completely filled

valence

francium is the ______ electronegative element

least

three classifications of materials are

metals ceramics polymers

optical properties of materials depend on their ________ characteristics

structural

deformation ________ resistivity in metals

increases

Materials’ properties depend on their _________

structure

highly porous materials are _______ conductors of heat

poor

what is not a property of metals?

ductile

high electrical conductivity

brittle

strong

brittle

materials used for space shuttles have ____ thermal conductivity

low

adding Si to Fe ______ magnetic permeability of Fe

increases

increasing carbon content increases ______ of steel

hardness

properties determined by an atoms electronic structure

chemical electrical thermal optical

atomic radius increases from ___________

right to left

covalent bonds are very _________

Strong

how many elements in the periodic table?

118

________ is the energy required to move electrons from an atom

ionization energy

the atomic number is equal to the

number of protons in each atom

the principle quantum number (n) determines

electron energy

bond hybridization is the combination of two or more _________

orbitals

what type of bonding does water exhibit

hydrogen

_________ properties are commonly observed in single crystals

anisotropic

dense ordered packing creates

lower energy

non dense random packing creates

high energy, not prefered

crystalline materiasl

atoms arrange in 3d arrays, typical of metals, ceramics and some polymers

noncrystalline materials

no periodic arrangement, occurs in complex structures and rapid cooling

simple cubic crystal structure (SC)

8 atoms in the corners of the cube

coordination number

number of touching atoms

atomic packing factor

volume of atoms in a unit cell/volume of unit cell

body centered cubic (BCC)

8 atoms at each corner, 1 in the center

face centered cubic (FCC)

8 atoms in corners of the cube, 6 atoms in center of each face

hexagonal close-packed (HCP)

6 atoms form hexagon on top and bottom, 3 form triangle in middle, 2 in center of each hexagon

single crystal

atoms in repeating array over the entire material

polycrystalline material

composed of many crystals

anisotropy

having a different value when measured in different directions

isotropy

same properties in all directions

polymorphism/allotropy

two or more distinct crystal structures for the same material

point coordinates

a lattice position in a unit cell

Atoms assemble into ___________ (ordered) or __________________ (disordered) structures

crystalline amorphous

common metallic crystal structures

FCC BCC HCP

Optical properties of materials doesnt depend on their structural characteristics T/F

true

the atomic weight of an atom is equal to the sum of its protons and neutrons T/F

true

which of the following is true about metals and heir alloys

not transparent to visible light

Materials science and engineering can be defined as the relationship among the structure, ___________, and processing

properties

Diamond is the materials with the highest thermal conductivity T/F

true

_______________ properties are responses of materials to the application of magnetic field

magnetic

Materials used in space shuttle thermal protection system have ________ thermal conductivity

low

Electrical resistivity _______________ as we increase the impurity content

increases

Which of the following statements is NOT true? (a) the processing cannot influence the structure

(b) all the properties of materials strongly depend on the structure of the materials

(c) structure depends on how the material was manufactured

(d) the characteristic of individual materials dictate how they can be processed

the processing cannot influence the structure

Deformation ___________________ electrical conductivity

decreases

A quick cooldown from a higher temperature attributes to which characteristics

(A) increase grain size

(B) decrease grain size

(C) No effect

(D) exponential increase of grain size

Decrease grain size

Highly porous materials are

Poor heat conductors, poor electrical conductors

Copper electrical conductivity is affected by

Temperature impurity deformation

Saltwater corrodes metal

Faster than fresh water

Why is graphine the best conductor

Thinness of material, high electron density

Electrical conductivity of metal could be increased by

Increasing temperature, increasing impurity atoms

What properties are attributed to ceramics

Brittle, hard

Material’s tendency to be magnetized

Permeability

What properties are attributed to polymers

Soft corrosion resistant insulator

Why are porous materials poor heat conductors

Presence of void spaces

_______ are hard, brittle, low thermal and electrical conductivity and can either be transparent, opaque, or translucent

Ceramics

What decreases a materials electrical conductivity

Increases impurities, temperature increase, deformation

Higher cooling rate will ________the hardness of steel

Increase

Which properties can be attributed to a mechanical property

Stiffness

Why is diamond thermal conductivity yet electrically insulative?

Strong covalent bonds, absence of carrier electrons, lower photon scattering

Metals have

High electrical conductivity, high thermal conductivity, ductility

What is the primary element of polymers

Carbon

What is affected by high temperatures

Thermal conductivity, electrical conductivity, magnetism

_______ __and__ __________ have low thermal and low electrical conductivity

Polymers and ceramics

What’s the strongest chemical bond

Covalent

What trend does ionization energy follow in the periodic table

Decreases from top to bottom, increases from left to right

What determines an element electron configuration at equilibrium

If valence shell is full

A ceramic would have what properties

Low thermal expansion

Examples of secondary bonding

Hydrogen bonds

What’s not affected by bond energy

permeability

Most polymers melt at a _______temperature than metallic solids

Lower

Metallic solids exhibit a _____, yet wide range of melting points

High

Metallic solids can be viewed as positive ions _______packed in a sea of valence electrons

Closely

What type of bonding do polymers have

Covalent and van der waals

What material has a high melting temperature and a small coefficient of thermal energy

Ceramics

What type of bonding do ceramics have

Ionic and covalent

What are characteristics of a covalent bond

Bonds involve electron sharing

What bond requires a large difference in electronegativity

Ionic

Which relationship describes the relationship between bond energy (E) and melting temperature (T_m)

Larger E, higher Tm

What is NOT a property of polymers

(A) low melting temperature

(B) low Young's modulus

(C) low coefficient of thermal expansion

(D) low bond energy

Low coefficient of thermal expansion

Which grouping of elements are inherently stable

Noble gases

Secondary bonding is why polymers are

Weak

Larger bond energy means

High stiffness, high melting temperature, low thermal expansion

Linear density of an atom

Number of atoms centered on the direction vector/length of the direction vector

What element characteristics do ceramics often have

Lighter elements

Which unit cell structure has an atomic packing factor of 0.68?

Body centered cubic

How many atoms per unit cell are in an FCC crystal structure

4

Which is true with crystalline materials

Typically metals

Crystalline materials are arranged in _________, 2D and 3D__ arrays

Periodic