Exam 1 Flashcards
Write the electron configuration for Fe3+ (the atomic # for Fe is 26)
Fe3+ has 23 e-
1s2 2s2 2p6 3s2 3p6 3d3 4s2 (would accept 3d5)
Define electronegativity
a measure of how strongly atoms attract bonding electrons to themselves
measures how tightly e- are bound to an atom
What is the nearest neighbor direction in FCC crystals? BCC crystals?
FCC: <110>
BCC: <111>
What are the 3 types of primary bonds discussed in this class?
Metallic
Ionic
Covalent
What are 2 examples of 0-dimensional (point) defects in crystals?
Vacancies
Frankel
Schottky
Substitutional
What are the 2 types of 1-dimensional (linear) defects in crystals?
Edge
Screw
(With perpendicular symbol before each)
What is one type of 2-dimensional (planar) defects in crystals?
Grain boundary
What is a Schottky defect?
Both cation and anion missing from an ionic structure. 2 vacancies
What is a Frankel defect?
2 cations occupy one lattice site. 1 vaccancy
What is a dipole?
A pair of equal and oppositely charged or magnetized poles separated by a distance. Associated with secondary bonding
Why are H bonds so much stronger than Van der Waals forces?
H only has one e-. when it gets pulled to one side, it leaves onyl the + nucleus exposed
What is the coordintation number for the BCC crystal structure? For the FCC structure?
BCC: 8
FCC: 12
What are hybrid orbitals? Give one example
sp orbitals combine to form a new bond geometry
sp2: sp3 orbitals in graphite, diamond
Define covalent bonding, when does it occur?
Adjacent atoms share electrons: occurs when electronegativities are equal to each other
Define metallic bonding
Lattice of + ion cores surrounded by a sea of e-
What is a side group?
Atom or molecule attached to the carbon backbone of a polymer chain.
What is the difference between thermosets and thermoplastics?
Thermoplastics can be heated: reformed. Thermo sets will char before flowing.
Write the electron configuration for calcium (Ca, atomic # = 20)
1s2 2s2 2p6 3s2 3p6 3d2
Define a thermoset polymer
- A polymer that will burn/char before reforming/melting when heated.
- A polymer with primary bonds along the chains and between adjacent chains
Van der Waals bonds involve what type of atoms or molecules?
dipoles
Two atoms with similar electronegativities will form what type of bond?
covalent
What are the 4 Hume-Rothery conditions that must be satisfied for complete miscibility of one atom in another
- Same valence
- Same crystal structure
- Similar atomic size
- Similar electronegativities
What are 3 types of point defects?
vacancy, interstitial, substitution, Schottky, Frenkel
T/F: Violation of one or more Hume-Rothery conditions means that two elements are completely soluble in one another
False
Define tacticity
Tacticity is the pattern of the side groups, following in attaching to a polymer chain: one-sided (isotactic), random (atactic), alternating (syndiotactic)
What is a grain? What is a grain boundary?
Grain- region of crystalline material in which the orientation of the unit cell is constant
Grain boundary- region of crystalline material where two grains connect.
What is the Burgers vector?
It defines a unit of motion of a dislocation line
What are the 2 types of dislocations discussed in class?
Screw and edge
Define a crystalline metal
A crystalline material possesses long-range order
The vertical columns of atoms on the periodic table are referred to as
groups
The state of each electron orbiting an atom is defined by ______ quantum numbers
4
Why are the values of atomic mass for each element on the periodic table not whole numbers?
The are weighted averages of all isotopes of the material
Consider the PE (bond energy) between 2 adjacent atoms. What is the relationship between the force felt by the atoms and the bond energy? What is the value of the force at the equilibrium spacing?
F=(dE/da)
When the atoms reach equilibrium spacing (a_o) F=0
Write the electron configuration for calcium (Ti2+, atomic # = 22)
1s2 2s2 2p6 3s2 3p6
Two atoms with very DIFFERENT electronegativities will form what type of bonds?
Ionic
What are 2 types of line defects?
1D: edge, screw
(perpendicular symbol) dislocations
T/F: Violation of one or more Humer-Rothery conditions means that 2 elecments are completely insoluble in one another
False
What are the 3 types of polymer tacticity?
isotactic (1 side)
atactic (random)
syndiotactic (alterating)
In what type of materials do Schottky defects occur?
Ceramics
What is a Frenkel defect? In what materials does it occur?
2 cations occupy 1 lattice side, 1 vacancy
Ceramics
What is the Pauli Exclusion Principle?
the quantum mechanical principle which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously
The principal quantum number defines the _____ of an orbital
size
The second quantum number defines the _____ of an orbital
shape
How many crystal systems are there?
7
Number of Bravais Lattices are
14
Length of unit cell edges and angle between crystallographic axes are reffered to as
lattice constants
Atomic packing factor for FCC is
.74
Ionic packing factor or MgO is
.627
What are miller indices?
Miller indices give position to lattice planes
Define equilibrium bond length a_o? What is the magnitude of the resultant of Columbic attractive and repulsive force at the bond length?
Equlilbrium bond length occurs when the attractive force is equal to the repulsive force Fc = Fr
Fc + Fr = 0
What is co-ordination number?
the # of adjacent ions or atoms surrounding a reference ion or atom
