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FMS > Fundamentals > Flashcards

Fundamentals Flashcards

1
Q

Define stress and strain

A 
Stress = F/A
Strain = Change in X/X
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2
Q

What is the UTS, Yield point, Failure point, plastic and elastic regions ?

A

UTS - most strain sample can endure
Yield point - when plastic deformation begins
Failure point - stress at which sample fails
Elastic region - follows Young’s modulus, all deformation recoverable
Plastic region - non-linear and permanent deformation

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3
Q

Draw and describe the features of an atom

A

Nucleus - where most mass centred

Surrounded by discrete e- shells, whose energy increases as distance increases

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4
Q

How does an electron move between shells?

A

e- absorbs photon and is excited to new shell (if energy high enough)
Then deexcites to lower shell which is more stable and emits a photon with energy equivalent to difference in shell energies - each atom has unique set of shells

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5
Q

What 4 things are used to define an e- energy?

A

Shell number (1 -> 3)
Sub shell number (s,p,d,f)
Orbital (x, y, z)
Spin number (-2 -> 2)

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6
Q

Which e- shells fill first?

A

Lowest energy ones - closest to nucleus

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7
Q

How many sub shells, orbitals and electrons can the 4 shells have?

A 
Each orbital can hold 2 e-
K - S sub shell, 1 orbital 
L - S and P s-shell, 1 and 3 orbitals 
M - S,P,D - 1,3,5 orbitals
N - S,P,D,F - 1,3,5,7 orbitals
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8
Q

How many orbitals do the P and F sub shells contain?

A 
P = 3
F = 7
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9
Q

What does 2p6 mean? (in e- shell terms)

A

2nd shell, P subshell, contains 6 e-

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10
Q

What are valence e-?

A

Electrons on the outer most shell of the atom - the ones that react

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11
Q

What is the atomic number and atomic mass number?

A

Atomic number = protons in nucleus

Mass number = average mass of all isotopes of atom

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12
Q

What is an isotope?

A

Atom which has more neutrons that another one of the same type

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13
Q

What is relative atomic mass?

A

1 RAM = 1/12 of mass of carbon 12 = 1U

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14
Q

Calculate RAM of chlorine which is 75% 35/17 chlorine and 25% 37/17 chlorine

A

0.75 x 35u + 0.25 x 37u

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15
Q

Why aren’t noble gasses reactive?

A

Because they have full outer shell so are most stable

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16
Q

What is e- affinity?

A

Energy released when an e- is added to a neutral atom - atoms with lots of valence e- have high affinity

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17
Q

What is ionisation energy?

A

Energy required to remove an e- from a neutral atom

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18
Q

What is electronegativity? And which atoms have high electronegativity?

A

A measure of how likely an atom is to gain an e- during a reaction
Atoms with high e- affinity and high ionisation energy (those with lots of valence e-)

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19
Q

What is an ionic bond?

A

Transfer of e- between atoms to complete both outer shells -> only done with different elements
Creates oppositely charged atoms which strongly bond together and have direction

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20
Q

What is coulombs equation and what does each symbol stand for?

A

Bond energy = 1/4πε . Q1.Q2. 1/r . B/r^n

ε = universal constant, B = empirical constant, Q1/2 = charge on ions, r = separation distance, n = constant

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21
Q

What is a covalent bond?

A

Both atoms donate an e- and share between them to complete outer shells, can have more than one covalent bond at a time (max = 8) & can happen between similar or dissimilar atoms
Bonds are very strong and directional

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22
Q

Can a bond be purely ionic?

A

No - all atoms have some level of electron negativity so there will always be some element of covalent bonding with in the ionic bonds

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23
Q

What is a metallic bond?

A

Metallic bonding causes metals to form a structure, each are donates delocalised e- to form an e- cloud in material - this cloud stops the +ve charged atoms from repelling and e- density changes throughout material
Bonds are non-directional

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24
Q

Rank them primary bonds in order of strength

A

Covalent bonds
Ionic bonds
Metallic bonds

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25
Q

Describe a Van der Waals bond

A 
Secondary bond (no e- movement) caused by ionic attractions between atoms 
Weak bond
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26
Q

Sketch the lennard-Jones potential energy curve and what does it show?

A

Separation distance vs potential energy
X^2 curve which drops below x axis and then Asymptotes with x axis
Minimum of curve = minimum energy distance = equilibrium distance

27
Q

Define a unit cell

A

Must have translational symmetry, contains all information of the cell, microstructure can be used to describe material properties, generally 3D shapes

28
Q

Define a motif and primitive unit cell

A

Motif - a group of atoms that are repeated at every point in the lattice (usually 2/3 atoms)
Primitive unit cell - smallest possible unit cell that still represents the entire structure

29
Q

How many crystal systems are there? And what are they?

A 
Triclinic 
Monoclinic 
Orthorhombic 
Tetragonal
Hexagonal
Cubic
Trigonal
30
Q

How many bravais lattices are there?

A

14, all others are repeats

31
Q

Draw the four possible unit cells

A

BCC
FCC
HCP
Primitive cubic

32
Q

How many atoms are in each of the four unit cells?

A

BCC - 1 in each corner (shared by 8), 1 in centre (not shared) = 2
FCC - 1 in each corner, 1 in each face (shared by 2) = 4
HCP - 7 on both faces (6 shared by 6, 1 shared by 2), 3 in centre = 6
Primitive cubic - 1 in each corner = 1

33
Q

What are the 3 lattice characteristics?

A 
Lattice parameter (vector from one atom to another) 
Angle between translation vectors 
Coordination number (atoms in each lattice)
34
Q 
What do each of the following mean? 
[101] 
<101>
(101)
{101}
A

[101] - lattice point or directon vector
<101> - family of coordinates - 100,001,1-10
(101) - 101 plane
{101} - family of planes

35
Q

How are -ves written in lattice parameters?

A

Bar over the negative number

36
Q

What’s happens to ions when temperature increases?

A

Lattice vibrates more, when T is high enough atom moves enough to break bonds (happens in melting) and sometimes form new ones if they’re energetically favourable (changing lattice structure)

37
Q

Why does an element have a higher Tm than another

A

Stronger bonds/more bonds per area means more energy required to break intermolecular bonds = higher T needed = higher Tm

38
Q

What are used to determine points on planes?

A

Miller indices

They are the reciprocals of lattice coordinates (E.g. 2 = 1/2)

39
Q

What is the Miller indices of a plane that crosses the x axis at 1, and is parallel to the z and y axis

A

(1,0,0) as parallel = 1/infinity

40
Q

What’s the Miller indices of a plane that crosses the x at 1/3, the y at 1 and is parallel to the z axis?

A

(3,1,0)

41
Q

What is the Miller indices of a plane that intersects at (0,0,0), and how are planes grouped?

A

1/0 is impossible meaning plane can’t occur, must translate the plane and then take the Miller indices
E.g. (1,1,1) (0,0,0)
The same as vectors, {1,0,0} = (0,0,1) = (0,-1,0) = (0,1,0)

42
Q 
When are [] + <> used? 
When are () + {} used?
A 
[] = direction, <> = group direction 
() = plane, {} = group of planes
43
Q

How are planes and plane spacing related?

A

Bigger density of planes = reduced space between them

d = 1/ square root (h2/a2 + k2/b2 + l2/c2)

44
Q

What can the dot and cross product show?

A 
Dot = finds angle between planes 
Cross = direction normal to both planes
45
Q

What’s an interstitial site ?

A

Gaps between atoms in a crystal structure that can accommodate a smaller atom

46
Q

What is the atomic packing factor? And what are the unit cell volumes for BCC and FCC structures?

A

% of the lattice which is filled, atom volume (atoms.1.25.πr3) unit cell volume
BCC = 4r/root 3
FCC = 2r.root 2

47
Q

Calculate the interstitial sizes for BCC

A

In BCC interstitial size = a = 4r/root 3 = 2(R + r)
r = R (-1 + 2/root 3)
Where r = atom that could fit in interstitial site

48
Q

What are the atomic packing factors of BCC, FCC and HCP?

A 
BCC = 68%
FCC = 74% 
HCP = 74%
49
Q

What is meant by coordination number?

A

Number of nearest neighbours that an atom has (ie how many atoms are close to it)

50
Q

What are the interstitial sites in an FCC lattice?

A

6 tetrahedra sites
13 octahedral sites
FCC has fewer, but much bigger, interstitials than BCC

51
Q

What’s the difference between cation and anion?

A

Cation +ve charged and smaller

Anion -ve charged and bigger

52
Q

What structure do ionic compounds have?

A

Always FCC

53
Q

Describe coulombs force

A

Electrostatic potential energy causing atoms to repel or attract = energy of bond
Ebond = Eattract + Erepuls
= Q1.Q2/4π.εo.r2 + B/r^n
Where Q = valence.e, r=radius, B = imperial constant

54
Q

When is the drop in electrostatic potential energy minimised?

A

When a structure is not close packed so atoms can be the equilibrium distance between each other

55
Q

What is the loss in electrostatic energy? And what is meant by the mandelung constant?

A

Elost = M/a . e2/4π.εo
Where a= lattice parameter, e = e- charge, M = mandelung constant = measure of a structures efficiency at reducing electrostatic energy

56
Q

What things dictate an ionic compounds structure?

A

Charge - all ionic compounds must have 0 charge
Relative size - stable if ions can can fit into interstitials or successfully strain lattice
Mandelung constant - if more than 1 structure can form, lowest mandelung will form as lowers energy

57
Q

Describe the structure of a silicon crystal

A

Each atom is covalently bonded with 4 other Si, all bonds have the same length and strength, diamond structure is formed with atoms every [1/4,1/4,1/4]
Some ionic bonds are formed

Diamond is same structure but with C instead of Si

58
Q

How does x-ray diffraction work out lattice spacing?

A

X-rays onto lattice, reflection at interface, time between reflections = distance between interfaces = distance between atoms/layers

59
Q

What is Bragg’s law and what does it show?

A

Nλ = 2d sinθ
Where d = a/root(h2 + k2 + l2)
Shows at which θ a constructive interference is observed

60
Q

Define a constructive and destructive interface

A

Constructive - waves are in phase = an integer λ apart = maxima and minima
Destructive - waves in antiphase = 1/2 integer λ apart = only minima

61
Q

How can reflections be used to identify a crystal structure?

A

When many waves interfere = bigger chance of destructive interface
More planes = more waves = more destructive interference so closer packed structure = less waves
(FCC has less than BCC which has less than cubic primitive)

62
Q

What are forbidden reflections in primitive cubic, FCC, BCC and bass centre lattices?

A

Forbidden reflections = when destructive is set up
Primitive = no forbidden
BCC = when h + k + l = odd
FCC = h, k, l aren’t all odd/even (E.g. (1,2,3)
Base centre = all reflection forbidden

63
Q

How does a diffractometer work?

A

Sample in centre, x-ray source in with λ calculate using Bragg’s law = constructive interface, moving x-ray detector move around sample to detect x-rays
Amount of reflections etc will give idea about structure

FMS (6 decks)

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