mse exam 2

what 4 things to electrons do in a solid

1. bonding

2. electronic properties

3. optical properties

4. magnetic properties

quantum numbers

ways to describe how the electrons affect the shape of the atom

principal quantum number is denoted by what letter

n

what does the principal quantum number mean

the DISTANCE of the electron from the nucleus

if you have a bigger n, does it mean you are closer or further from the nucleus?

bigger n = further from nucleus

what is the 2nd quantum # called

azimuthal

what does 2nd quantum # represent

the shape of the electron shells (s, p, d, f)

is it easier for electrons to bond if they are closer or further from the nucleus

easier if they are further

what are d and f shells good for (2)

1. magnetism

2. fluorescence and phosphorescence

to maximize magnetization, what do we want to maximize?

the number of unpaired electrons

how does the number of unpaired electrons affect magnetism?

it makes the electrons have a higher magnetic spin, giving a higher saturation magnetization and higher remanence

fluorescence def

is FLEETING and is immediate

phosphorescence

is SUSTAINED and doesn’t go away after the energy has been supplied

how do the d and f shells do fluorescence and phosphorescence

the split energy levels allows the e to get excited to a HIGHER STATE, which will release light

3 types of primary bonds

1. ionic

2. covalent

3. metallic

2 types of secondary bonds

1. van der waals

2. hydrogen bonds

do ionic bonds share or transfer e?

transfer, creates cation and anion, has coulombic attraction

how to estimate ionic bond strength?

use coulombic attraction formula

repulsive force formula

F = -B/x^12

do ionic bonds depend on orientation / directionality?

NOOOO, they are non directional

what happens if you plastically deform an ionic solid?

FRACTURES bc 2 pos and 2 neg are next to each other, reason why CERAMICS are BRITTLE

do covalent bonds share or transfer e

they SHARE e, have orbital overlap

types of materials w covalent bonds

semiconductors + POLYMERS

are covalent bonds strong or weak

generally strong

ex of covalent bonds

C-C, C-H, Si-Si

are covalent bonds directional or not

YES DIRECTIONAL

metallic bonds def

sea of electrons, valence e are delocalized and shared

are metallic bonds directional

NO

what happens if you plastically deform a metal?

since e are SHARED, metals allow plastic deformation

rank ionic, covalent, and metallic solids from most to least DENSE

metallic (most), ionic, covalent

metallic solid packing %

74%

ionic solid packing %

67%

why is ionic packing less than metallic

bc of the size difference of the cations and anions

covalent solid packing %

34%

why is covalent packing less than ionic

bc of the directional bonds in covalent, makes it have a lot of OPEN space

3 types of van der waals bonding

1. induced dipole - induced dipole (LDF)

2. dipole - induced dipole

3. dipole - dipole

induced dipole - induced dipole (LDF)

very weak electrostatic attraction, caused by a RANDOM FLUCTUATION in e clouds

dipole - induced dipole bonding

a permanent dipole INDUCES a non energized atom, makes a new induced dipole

ex of dipole - induced dipole bonding

PVC interacts w PET

dipole - dipole bonding

2 permanent dipoles bond

is dipole-dipole weaker or stronger than LDF?

dipole-dipole is STRONGER

ex of dipole-dipole bonds

PVC

do polymers have a high or low elastic modulus

low, are NOT stiff

why do polymers have such low elastic moduli?

bc its held together by WEAK LDF VAN DER WAALS bonds

why is PVC a little stronger than polymers?

bc its held w dipole-dipole which is stronger than LDF

simplified coulobmic attraction formula

A/x²

when do we have equilibrium for ionic bonds?

when the sum of attractive and repulsive adds to 0

how to model stiffness w a force v distance graph

take the SLOPE near the equilibrium point on the graph

does a smaller slope mean it is less stiff on a force v distance graph

yes, small = weak

what is the integral of the force curve

the energy v distance curve

what does the curvature of the energy graph tell us

how STIFF the material is

if you have a high curvature, is it stiff or weak

it is stiff, as it takes MORE energy to separate/expand the material

barrier energy def

how much energy needed to overcome the reaction

if thermal > barrier energy

the rxn is LIKELY to happen

if thermal < barrier energy

the rxn is UNlikely to happen

when T>0, are there vibrations in the material

YEA bc temp is nonzero

which curve would have a higher melting point?

the one that as a DEEPER well, the curve that is further from the x axis

which material has the higher thermal expansion coefficient?

the one with the THINNER well, bc its avg bond length doesnt increase as fast when temp is applied

the more SYMMETRICAL the energy well, the lower the CTE

another way to express well depth

change in enthalpy of fusion (∆H_f)

if ∆H_f increases, what happens to T, CTE, and E (energy)?

T goes up

CTE goes down

E goes up

what happens if there is lattice mismatch

the material will have poor CONDUCTION

what determines density in a metal?

the actual element’s density

what determines density in a ceramic?

the ARRANGEMENT of the atoms

what determines density in a polymer?

the percentage of OPEN SPACE

density is equal to what

mass / volume

does atomic mass or atomic radius increase faster?

atomic MASS

what does packing help a solid with

it helps to MINIMIZE the total energy of the system

coordination number def

how many NEIGHBORS a specific atom has

what is the coordination number for FCC packing

12

what is the coordination number for HCP packing

12

what does FCC stand for

face centered cubic

what does HCP stand for

hexagonal close packed

does FCC have 2 or 3 unique layers?

3 (ABC stacking)

does HCP have 2 or 3 unique layers?

2

is the coordination number SRO (short range order) or LRO