Chapters 1, 2, 3 (intro, atomic structure and bonding, crystal structure) Flashcards
1
Q
What is a property?
A
the response of a material to an external effect
2
Q
Examples of properties
A
Mechanical, electrical, deteriorative, optical, magnetic, thermal
3
Q
what are the classes of materials
A
Metals, ceramics, polymers
4
Q
what is a metal
A
inorganic metallic elements
5
Q
name 2 properties of metals
A
- Thermal and electrical conductors 2. Strong and ductile
6
Q
why are metals good conductors
A
because they have free electrons
7
Q
what is an alloy
A
a combination of 2 or more metals and non-metals
8
Q
What is a ceramic
A
a compound of metals and non-metals
9
Q
name 5 properties of ceramics
A
- Hard and strong 2. Brittle 3. Resist high temps 4. Low density 5. electrical insulators
10
Q
common example of a polymer
A
plastic
11
Q
what is a polymer
A
a long chain molecule and network usually based on carbon
12
Q
name 3 properties of polymers
A
- electrical insulators. 2. low density 3. low operating temperatures
13
Q
what are composites
A
a mixture of 2 or more materials
14
Q
what is unique about semi conductors
A
they share properties of both insulators and conductors
15
Q
what types of materials are used in “Bio-Materials”
A
all
16
Q
order of density of materials
A
metals
ceramics
polymers & composites
17
Q
order of stifness
A
metals and ceramics
composites
polymers
18
Q
order of strength
A
metals
composites
ceramics
polymers
19
Q
order of electrical conductivity
A
metals
semi conductors
ceramics and polymers
20
Q
what do properties of materials depend on
A
bonds between atoms
atomic packing
21
Q
what is an atom comprised of
A
Proton + neutron + electron
22
Q
where is the mass of the atom located
A
nucleus
23
Q
where is the volume of the atom located
A
electron cloud
24
Q
what does the atomic # dictate
A
of protons
25
what type of electrons determine important properties
valence electrons
26
what are electroPOSITIVE elements
metallic elements that GIVE UP outer electrons to become CATIONS
27
what are electroNEGATIVE elements
non metals that ACCEPT electrons to become ANIONS
28
electronegativity
the tendency to attract electrons
29
essentially, why do atoms bond together?
to reduce overall energy
30
when is equilibrium reached
when Fa+Fr=0 OR when the overall energy is at a minimum
31
what is bonding energy
the energy required to break the bonds
32
what would a higher bonding energy do
stronger bonds=higher strength=higher melting temp
33
types of primary bonds
1. Ionic
2. Covalent
3. Metallic
34
types of secondary bonds
1. Van der Waals
| 2. Dipole fluctuations
35
Primary, Secondary; Physical Chemical. MATCH THEM
Primary=Chemical, Secondary=physical
36
between what types of elements are ionic bonds typically found
metals and non metals
37
what type of material are ionic bonds usually found in
Ceramics
38
why do ions pack together
to maintain neutrality
39
materials which are ionically bonded are what? (3 things)
1. very strong
2. brittle
3. insulators
40
Covalent bonds
sharing of electrons, they try to attain noble gas configs
41
degrees between sp^3 orbitals
109.5
42
%Ionic Character formula
[1-exp(-0.25(Xa-Xb)^2)]x100
43
what are 'ion cores'
closely packed metal ions in ordered arrangements
44
what type of bonding are SEAs of electrons found
Metallic
45
Metallic bonds are insulators or conductors
conductors (free electrons)
46
Secondary bonding
low energy-weak bonds
47
what are secondary bonds based on
dipoles(separation of charge)
48
Where are Van der Waals forces found
between 2 adjacent polar molecules
49
What does Amorphous mean?
NO REPEATING ORDER or pattern in bonds, aka short range order
50
What are crystals?
Atoms bonded together in a REGULAR 3D patter, aka long range
51
what materials are crystalline Patterns found in?
Ceramics, Metals, Some polymers
52
What are space lattices
the arrangement of atoms
53
What is a unit cell
the smallest repetitive unit which is part of the lattice pattern (it must display the minimum # of features but never repeat any)
54
name the 3 types of densely packed structures
1. Body centered cubic(BCC)
2. Face centered cubic (FCC)
3. Hexagonal close packed (HCP)
55
formula for atomic packing factor
volume of unit cell occupied by atoms/ total unit cell volume
56
where do atoms touch each other in BCC
along the cube diagonals
57
where do atoms touch each other in FCC
along the FACE diagonals
58
Coordination # of BCC, FCC & HCP respectively
8, 12, 12
59
Atoms per unit cell of BCC, FCC, HCP respectively
2, 4, 6
60
crystal density formula
density=number of atoms in unit cell * Molar Mass/volume of unity cell * Avogadros #
61
what is polymorphism/allotropy
elements in which more than 1 crystal form can exist depending on temperature
62
which is the most & least symmetric crystal structure
cubic & tricrilic respectively
63
linear desnity formula
number of atoms/ unit length of direction vector
64
Planar density formula:
(atoms/2D repeat unit)/(area/2D repeat unit)
65
Single crystal
when a piece of material is made of 1 single crystal
66
Polycrystals
Many different crystals, with varying orienations
67
what is a grain boundary
the boundary line at which crystal grains meet
68
If a property varies with direction, it is said to be...
Anisotropic
69
If a property doesn't vary with direction, it is said to be...
isotropic
70
describe creep
the tendency for a material to lengthen over time under load
71
The degree to which a material will creep is dependant on what?
the number of grain boundaries
72
state bragg's law formula
n(lambda)=2d(hkl)sin(theta)
73
what can be said about the position of atoms which are covalently bonded?
their elements will be close on the periodic table
74
Basically, why are metals ductile?
Non-directional bonding-->fewer restrictions-->can withstand larger forces before bonds break.
ALSO, since metals have free electrons, this allows their structures more freedom, promoting ductility.
75
Which is the only Non-Crystalline ceramic? And what is another word for this category?
Glass. Amorphous
76
what are space lattices?
the patterns in which atoms prefer structuring themselves in
77
when we refer to lattice constant, which variables are we talking about?
a, b, c
78
List the properties of BCC (3)
1. 4R=sqrt3*A
2. coordination # =8
3. 2 atoms/unit cell
4. APF=0.68
79
List the properties of FCC (4)
1. 4R=sqrt2*A
2. coordination # = 12
3. 4 atoms/unit cell
4. APF=0.74
80
List the properties of HCP(2)
1. 6 atoms/ unit cell
| 2. coordination #=12
81
what crystal SYSTEM is common for all CUBIC crystal STRUCTURES
a=b=c and usually, alpha =beta=gamma=90deg
82
how is a crystallographic direction denoted?
[xyz]
83
what does the family of directions denote?
all edges of a cube
84
what does family denote?
all internal diagonals
85
what does the family denote?
all face diagonals
86
what can be said about directions and planes with the same indices in cubic systems
the direction is perpendicular to the plane
87
if the electronegativity value of an element is high (ie near 4), what will it typically do to electrons
acquire/attract them
88
A balance of [these] forces determines the inter-atomic spacing
Repulsive and attractive forces
89
H2 would have which type of bonding and why
covalent, similar electronegativity, same number of valence electrons require to fill first orbital
90
describe fluctuating dipoles
when the atomic nucleus and electron cloud are not symmetrical, secondary bonding occurs between two adjacent molecules due to the charge separation
91
briefly describe why when water freezes, it expands
when water freezes, there are 4 hydrogen bonds found between 2 h20 molecules. these 4 bonds are relatively open and spaced apart, causing this expansion
92
chapter 2 question
| how and what do alpha, melting temperature and bond length depend on?
they depend on Eo(bonding energy). the larger Eo, the large those constants.
93
is energy higher or lower for denser packed structures?
lower
94
which materials have the simplest crystal structures
metals
95
what happens if you change the sign of all the indices of a direction?
it would give the exact opposite direction
96
what can be said about two parallel planes
they are equal and will have the same miller indices
97
how do we denote a crystallographic plane?
(hkl)
98
how do we denote a family of planes?
{hkl}
99
what does the {100} family of planes denote?
all faces of a cube
100
In FCC, what are the close packed planes?
{111}
101
In HCP, what are the close packed planes?
(0001)
102
Although BCC is not as close packed, which is its most densely packed plane?
{110}
103
what is the stacking sequence of FCC
ABCABCABC
104
what is the stacking sequence of HCP
ABABABABABAB
105
give a well-known example of an Anisotropic material
wood
106
how might one increase the Creep on a material
increase the temperature
107
what effect does increasing the # of grain boundaries have on creep?
the material will creep more
108
would properties in metal typically be iso or anisotropic?
isotropic
109
why is the diffusion coefficient greater C in alpha-iron BCC rather than C in gamma-iron FCC
since the atomic packing factor is less in BCC than it is in FCC, this means there is slightly more interstitial space for the atoms to move about in, making it faster to diffuse
110
are covalent bonds directional
yes, they are directional
111
true or false and why? when ro (distance) of 2 atoms is at equilibrium, the binding energy is 0
FALSE! the change in binding energy is 0, not the actually value, the binding energy will be at a minimum
