Chapter 2

Question 1

Define: Valance Electrons

Answer 1

Outer shell electrons; determine much of an atom’s chemical affinity for other atoms

Question 2

Define: Primary vs. Secondary Bonds

Intra vs. Inter Molecular Forces

Answer 2

Primary Bonds: characterized by strong atom-to-atom attractions that involve the exchange of valence electrons (ionic, covalent, metallic)

Secondary Bonds: Involve attraction forces between molecules, or inter-molecular forces (dipole, London, hydrogen)

Question 3

Define: Ionic Bonds

Answer 3

Bonds in which atoms of an element that give up an outer electron(s) to atoms of another element in order to increase both atom’s electron count in the outermost shell to 8.

Question 4

Define: Covalent Bonds

Answer 4

Bonds in which electrons are share between atoms in their outermost shell to achieve a stable set of 8.

Question 5

Define: Metallic Bonding

Answer 5

To fill incomplete outermost orbits of most metallic elements, electrons are shared atom-to-atom in a continuously flowing manner, providing good conductivity.

Question 6

Define: Alloptropic

Answer 6

Name given to metals or other materials that change their lattice structure due to temperature changes. (ex. BCC to FCC to HCP)

Question 7

Define: Point Defects

Answer 7

Imperfections in the crystal structure involving either a single atom or a few atoms. Imperfections include vacancy, ion-pair vacancy, interstitial (extra atom), or displaced ions (atom misplaced in lattice strucutre)

Question 8

Define: Vacancy

Answer 8

Missing atom within a lattice structure.

Question 9

Define: Interstitialcy

Answer 9

Produced by the presence of an extra atom in the strucuture

Question 10

Define: Line Defect

Answer 10

A connected group of point defects taht form a line in the lattice structure (dislocations)

Question 11

Define: Edge Dislocation

Answer 11

Edge of an extra plane of atoms that exists in the lattice

Question 12

Define: Screw Dislocation

Answer 12

Spiral within the lattice structure wrapped around an imperfection line (shearing)

Question 13

Define: Plastic Deformation

Answer 13

If mechanical stress reaches a high value relative to the electrostatic forces holding the atoms in their lattice positions, a permanent shape change occurs

Question 14

Define: Slip

Answer 14

Involves the relative motion of atoms on opposite sides of a plane in the lattice, called the slip plane.

Question 15

Define: Slip Plane

Answer 15

Plane of lattice in which atoms on opposite sides move apart from one another

Question 16

Define: Slip Direction

Answer 16

Preferred directions in which slip is more likely to occur; depends on the lattice structure

Question 17

Define: Grains

Answer 17

In metals, the millions of individual crystals with their own unique lattice and orientation.

Question 18

Define: Polycrystalline

Answer 18

When grains are collectors oriented randomly within a block of metal, it is known as polycrystalline.

Question 19

Define: Grain Boundary

Answer 19

As crystals grow within the metal, they interfere with one another, forming at their interference a surface defect, or grain boundary. Consists of a transition zone I which the atoms are not aligned with either grain.

Question 20

Define: Strain Hardening

Answer 20

Grain boundaries (imperfections) in metals that interrupt the continued movement of dislocations, make the metal stronger as it is deformed. Therefore, the more grains and grain boundaries, the stronger the metal.

Question 21

Define: Amorphous

Answer 21

When materials have a noncrystalline form in their solid state