Exam 1

Question 1

Write the electron configuration for Fe3+ (the atomic # for Fe is 26)

Answer 1

Fe3+ has 23 e-

1s2 2s2 2p6 3s2 3p6 3d3 4s2 (would accept 3d5)

Question 2

Define electronegativity

Answer 2

a measure of how strongly atoms attract bonding electrons to themselves
measures how tightly e- are bound to an atom

Question 3

What is the nearest neighbor direction in FCC crystals? BCC crystals?

Answer 3

FCC: <110>
BCC: <111>

Question 4

What are the 3 types of primary bonds discussed in this class?

Answer 4

Metallic
Ionic
Covalent

Question 5

What are 2 examples of 0-dimensional (point) defects in crystals?

Answer 5

Vacancies
Frankel
Schottky
Substitutional

Question 6

What are the 2 types of 1-dimensional (linear) defects in crystals?

Answer 6

Edge
Screw
(With perpendicular symbol before each)

Question 7

What is one type of 2-dimensional (planar) defects in crystals?

Answer 7

Grain boundary

Question 8

What is a Schottky defect?

Answer 8

Both cation and anion missing from an ionic structure. 2 vacancies

Question 9

What is a Frankel defect?

Answer 9

2 cations occupy one lattice site. 1 vaccancy

Question 10

What is a dipole?

Answer 10

A pair of equal and oppositely charged or magnetized poles separated by a distance. Associated with secondary bonding

Question 11

Why are H bonds so much stronger than Van der Waals forces?

Answer 11

H only has one e-. when it gets pulled to one side, it leaves onyl the + nucleus exposed

Question 12

What is the coordintation number for the BCC crystal structure? For the FCC structure?

Answer 12

BCC: 8
FCC: 12

Question 13

What are hybrid orbitals? Give one example

Answer 13

sp orbitals combine to form a new bond geometry

sp2: sp3 orbitals in graphite, diamond

Question 14

Define covalent bonding, when does it occur?

Answer 14

Adjacent atoms share electrons: occurs when electronegativities are equal to each other

Question 15

Define metallic bonding

Answer 15

Lattice of + ion cores surrounded by a sea of e-

Question 16

What is a side group?

Answer 16

Atom or molecule attached to the carbon backbone of a polymer chain.

Question 17

What is the difference between thermosets and thermoplastics?

Answer 17

Thermoplastics can be heated: reformed. Thermo sets will char before flowing.

Question 18

Write the electron configuration for calcium (Ca, atomic # = 20)

Answer 18

1s2 2s2 2p6 3s2 3p6 3d2

Question 19

Define a thermoset polymer

Answer 19

• A polymer that will burn/char before reforming/melting when heated.
• A polymer with primary bonds along the chains and between adjacent chains

Question 20

Van der Waals bonds involve what type of atoms or molecules?

Answer 20

dipoles

Question 21

Two atoms with similar electronegativities will form what type of bond?

Answer 21

covalent

Question 22

What are the 4 Hume-Rothery conditions that must be satisfied for complete miscibility of one atom in another

Answer 22

1. Same valence
2. Same crystal structure
3. Similar atomic size
4. Similar electronegativities

Question 23

What are 3 types of point defects?

Answer 23

vacancy, interstitial, substitution, Schottky, Frenkel

Question 24

T/F: Violation of one or more Hume-Rothery conditions means that two elements are completely soluble in one another

Answer 24

False

Question 25

Define tacticity

Answer 25

Tacticity is the pattern of the side groups, following in attaching to a polymer chain: one-sided (isotactic), random (atactic), alternating (syndiotactic)

Question 26

What is a grain? What is a grain boundary?

Answer 26

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.

Question 27

What is the Burgers vector?

Answer 27

It defines a unit of motion of a dislocation line

Question 28

What are the 2 types of dislocations discussed in class?

Answer 28

Screw and edge

Question 29

Define a crystalline metal

Answer 29

A crystalline material possesses long-range order

Question 30

The vertical columns of atoms on the periodic table are referred to as

Answer 30

groups

Question 31

The state of each electron orbiting an atom is defined by ______ quantum numbers

Answer 31

4

Question 32

Why are the values of atomic mass for each element on the periodic table not whole numbers?

Answer 32

The are weighted averages of all isotopes of the material

Question 33

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?

Answer 33

F=(dE/da) | When the atoms reach equilibrium spacing (a_o) F=0

Question 34

Write the electron configuration for calcium (Ti2+, atomic # = 22)

Answer 34

1s2 2s2 2p6 3s2 3p6

Question 35

Two atoms with very DIFFERENT electronegativities will form what type of bonds?

Answer 35

Ionic

Question 36

What are 2 types of line defects?

Answer 36

1D: edge, screw | (perpendicular symbol) dislocations

Question 37

T/F: Violation of one or more Humer-Rothery conditions means that 2 elecments are completely insoluble in one another

Answer 37

False

Question 38

What are the 3 types of polymer tacticity?

Answer 38

isotactic (1 side) atactic (random) syndiotactic (alterating)

Question 39

In what type of materials do Schottky defects occur?

Answer 39

Ceramics

Question 40

What is a Frenkel defect? In what materials does it occur?

Answer 40

2 cations occupy 1 lattice side, 1 vacancy | Ceramics

Question 41

What is the Pauli Exclusion Principle?

Answer 41

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

Question 42

The principal quantum number defines the _____ of an orbital

Answer 42

size

Question 43

The second quantum number defines the _____ of an orbital

Answer 43

shape

Question 44

How many crystal systems are there?

Answer 44

7

Question 45

Number of Bravais Lattices are

Answer 45

14

Question 46

Length of unit cell edges and angle between crystallographic axes are reffered to as

Answer 46

lattice constants

Question 47

Atomic packing factor for FCC is

Answer 47

.74

Question 48

Ionic packing factor or MgO is

Answer 48

.627

Question 49

What are miller indices?

Answer 49

Miller indices give position to lattice planes

Question 50

Define equilibrium bond length a_o? What is the magnitude of the resultant of Columbic attractive and repulsive force at the bond length?

Answer 50

Equlilbrium bond length occurs when the attractive force is equal to the repulsive force Fc = Fr Fc + Fr = 0

Question 51

What is co-ordination number?

Answer 51

the # of adjacent ions or atoms surrounding a reference ion or atom