Midterm Material Notes
Class 1
Metallic bonding: Found in metals and alloys, 1, 2, or 3 valence electrons that are not bound to any particular atom in the solid. They drift throughout the entire metal. This results in a sea of electrons. These free electrons result in good electrical and heat conductivity. Coordination number is 8 or 12 (number of nearest neighbors).
Ionic Bonding
Found in compounds that are composed of both metallic and nonmetallic elements.
Metallic element gives up valence electrons to the nonmetallic elements.
Attractive forces from positive and negative ions
Ceramic materials: high melting temperatures, hard, poor conductors
Covalent Bonding
Electrons are shared between adjacent atoms resulting in stable electron configurations.
Many nonmetallic elemental molecules are covalently bonded. Polymeric materials have this bond.
Crystal Structure
Describe the crystal structure using an array of points or lattice.
The unit cell is the smallest number of atoms that describes the crystal structure.
FCC: aluminum, copper, gold, lead, nickel, silver.
Coordination number, number of nearest neighbors is 12.
Atomic Packing Factor
APF = volume of atoms in a unit cell Total unit cell volume
Crystallographic Planes and Directions
Crystallographic Directions: a vector with coordinates in the xyz axis system. The length of the vector is the smallest integer values. They are written [uvw] i.e. [111] This defines a direction.
Crystallographic Planes: Miller indicies are (hkl). Three numbers that define the orientation of a plane with respect to a given coordinate system. h = a/x k = a/y l = a/z
Defining a Plane
The plane cannot go through the origin of the cell.
The plane either intersects or parallels each of the three axes. The length of the planar intercept for each axis is determined in terms of the lattice parameters a,b,c
The reciprocals of these numbers are taken. A plane that parallels an axis may be considered to
Metallic bonding: Found in metals and alloys, 1, 2, or 3 valence electrons that are not bound to any particular atom in the solid. They drift throughout the entire metal. This results in a sea of electrons. These free electrons result in good electrical and heat conductivity. Coordination number is 8 or 12 (number of nearest neighbors).
Ionic Bonding
Found in compounds that are composed of both metallic and nonmetallic elements.
Metallic element gives up valence electrons to the nonmetallic elements.
Attractive forces from positive and negative ions
Ceramic materials: high melting temperatures, hard, poor conductors
Covalent Bonding
Electrons are shared between adjacent atoms resulting in stable electron configurations.
Many nonmetallic elemental molecules are covalently bonded. Polymeric materials have this bond.
Crystal Structure
Describe the crystal structure using an array of points or lattice.
The unit cell is the smallest number of atoms that describes the crystal structure.
FCC: aluminum, copper, gold, lead, nickel, silver.
Coordination number, number of nearest neighbors is 12.
Atomic Packing Factor
APF = volume of atoms in a unit cell Total unit cell volume
Crystallographic Planes and Directions
Crystallographic Directions: a vector with coordinates in the xyz axis system. The length of the vector is the smallest integer values. They are written [uvw] i.e. [111] This defines a direction.
Crystallographic Planes: Miller indicies are (hkl). Three numbers that define the orientation of a plane with respect to a given coordinate system. h = a/x k = a/y l = a/z
Defining a Plane
The plane cannot go through the origin of the cell.
The plane either intersects or parallels each of the three axes. The length of the planar intercept for each axis is determined in terms of the lattice parameters a,b,c
The reciprocals of these numbers are taken. A plane that parallels an axis may be considered to