Bme 111 Midterm 1

Front 1

Chemical bonds

Back 1

Form by interactions between the valence electrons

Front 2

Ionic bonding

Back 2

Transfer of electrons, non directional, hard but brittle, resistant to degradation, bad conductors.

Ex. Ceramic (alumina, calcium phosphate)

Front 3

Covalent bonding

Back 3

Sharing electrons, only non metals, directionality by geometry of sub shells, flexible —> easily deformed, not good conductors

Ex. Polymers (polyethylene)

Front 4

Metallic Bonding

Back 4

All electropositive, want to give up e-, valence electrons are floating around, conductive, easily formed and processed, susceptible to corrosion

Ex. Stainless steel, cobalt chrome, titanium and alloys

Front 5

Forces between atoms are determined by ____ and ____

Back 5

Charge and distance

Front 6

Bonding energy

Back 6

Energy needed to separate the two atoms

Front 7

Higher bond energies = _______ melting temps

Back 7

Higher

Front 8

The steeper the force curve, the _______ the material

Back 8

The greater the force needed to change interatomic distance, stuff the material

Front 9

Hydrogen bonding

Back 9

Electrostatic interaction between polar molecules

Front 10

_______ are crystalline materials

Back 10

Metals and ceramics

Front 11

Crystalline material

Back 11

Any material that has long-range orderly arrangement of atoms/ions that can be described by a unit cell

Front 12

Unit cell

Back 12

Smallest repeating unit

Front 13

Atomic hard sphere model

Back 13

Each atom is a hard sphere with a fixed volume

Front 14

Simple cubic

Back 14

One atom located at each corner of the unit cell

Front 15

Atomic packing factor

Back 15

Volume fraction occupied by atoms

APF = volume of atoms in a unit cell / tot unit cell volume

Front 16

Body centered cubic

Back 16

Additional atom in center of cube

Ex. Iron, chromium

Front 17

Face centered cubic

Back 17

Atom at the center of each face, APF highest of all struct

Ex. Aluminum, copper, gold, lead, platinum

Front 18

Coordination number

Back 18

Number of nearest neighbors

Front 19

Linear Density Equation

Back 19

LD = number of atoms centered on a direction vector / length of the vector

Front 20

Planar Density Equation

Back 20

PD = number of atoms centered on a plane / area of plane

Front 21

Coordination number

Back 21

Number of nearest neighbors of opposite charge

Front 22

Point defect: vacancy

Back 22

Missing atom in structure (extra space)

Front 23

Point defect: interstitials

Back 23

Extra atom in structure (crowding)

Front 24

Rules of solubility of metals

Back 24

1. Atomic radii of solvent & solute must be similar (<15% diff)

2. Solute and solvent have identical crystal structures

3. Metal prefers to dissolve into solution with higher valency (number of valence electrons) over a solution with low valency

4. Solute and solvent have similar electronegativities

Front 25

Which element is usually interstitial

Back 25

Carbon

Front 26

Shottky defect

Back 26

Vacancy in both cation and anion to maintain neutrality

Front 27

Frenkel defect

Back 27

Vacancy and interstitial pair created to maintain electroneutrality

Front 28

Diffusion in gas/liquid

Back 28

Occurs by random motion

Front 29

Diffusion in solids

Back 29

Occurs by jumping into neighboring lattice points/positions

Front 30

Vacancy diffusion

Back 30

Atom jumps to neighboring position with a vacancy

Front 31

Interstitial diffusion

Back 31

Interstitial atom jumps to nearby interstitial site

Front 32

Which is faster? Vacancy or interstitial and why?

Back 32

Interstitial because doesn’t require existence of vacancy

Front 33

Diffusivity depends on

Back 33

Temperature and activation energy

Front 34

The larger the activation energy, the _____ the diffusion coefficient

Back 34

Smaller

Front 35

The higher the temp, the _______ the diffusion coefficient

Back 35

Higher

Front 36

Flux

Back 36

Rate of change in mass or number of atoms across an area over a given time

Front 37

At a steady state, flux _______ it is _____

Back 37

Doesn’t change with time, constant

Front 38

Conservation of mass

Back 38

Rate of change in concentration in the box is equal to the flux into the box minus the flux out of the box