Flashcards in Chapter 2 Deck (21):
Define: Valance Electrons
Outer shell electrons; determine much of an atom's chemical affinity for other atoms
Define: Primary vs. Secondary Bonds
(Intra vs. Inter Molecular Forces)
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)
Define: Ionic Bonds
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.
Define: Covalent Bonds
Bonds in which electrons are share between atoms in their outermost shell to achieve a stable set of 8.
Define: Metallic Bonding
To fill incomplete outermost orbits of most metallic elements, electrons are shared atom-to-atom in a continuously flowing manner, providing good conductivity.
Name given to metals or other materials that change their lattice structure due to temperature changes. (ex. BCC to FCC to HCP)
Define: Point Defects
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)
Missing atom within a lattice structure.
Produced by the presence of an extra atom in the strucuture
Define: Line Defect
A connected group of point defects taht form a line in the lattice structure (dislocations)
Define: Edge Dislocation
Edge of an extra plane of atoms that exists in the lattice
Define: Screw Dislocation
Spiral within the lattice structure wrapped around an imperfection line (shearing)
Define: Plastic Deformation
If mechanical stress reaches a high value relative to the electrostatic forces holding the atoms in their lattice positions, a permanent shape change occurs
Involves the relative motion of atoms on opposite sides of a plane in the lattice, called the slip plane.
Define: Slip Plane
Plane of lattice in which atoms on opposite sides move apart from one another
Define: Slip Direction
Preferred directions in which slip is more likely to occur; depends on the lattice structure
In metals, the millions of individual crystals with their own unique lattice and orientation.
When grains are collectors oriented randomly within a block of metal, it is known as polycrystalline.
Define: Grain Boundary
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.
Define: Strain Hardening
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.