Chem 202 Notes
* 9/4/12
12.3 - crystal structures crystalline structure: possess rigid and long-range order; its atoms, molecules, or ions occupy specific positions (Exs. wax ,ice, sugar, salt, diamond, etc.) unit cell: basic repeating structural unit of crystalline solid
-there are seven types of unit cells coordination number: number of atoms surrounding an atom in a crystal lattice
-higher coordination number --> more tightly packed structure
3 types of cubic unit cells: -primitive cubic (sc) c#: 6 -body-centered cubic (bcc) c#: 8 -face-centered cubic (fcc) c#: 12
-a corner atom is shared by eight unit cells
-an edge atom is shared by four unit cells
-a face atom is shared by 2 unit cells
-a central atom is not shared between atoms
# of atoms in structures: sc: 1 atom bcc: 2 atoms fcc: 4 atoms
-atoms such as metals or noble gases are more tightly packed; these are possibly structures: -hexagonal close-packed structure (hcp): -cubic close-packed structure (ccp):
-edge length/radius are related: -sc: a = 2r -bcc: a = 4rt( r )/rt (3) or a = 2.309r -fcc: a = r*rt(8)
X-ray Diffraction: they utilize the scattering of X-rays to determine the structure of an atom
Bragg'sLaw:
12.4- Types of Crystals ionic crystals
-composed of anions/cations
-held together by coulomb forces
-anions are generally bigger than cations
-size and rel. size determines structure covalent crystals
-atoms are held together in an extensive 3-D network entirely by covalent bonds molecular crystals
-the lattice points are occupied by molecules
-attractie forces are dispersion, dipole-dipole, and/or H-bonds metallic crystals
-every lattice point is occupied by an atom of the same metal
-electrons are delocalized over the entire crystal (makes it a good conductor)
-the delocalization keeps the crystal together
12.5- Amorphous Solids amorphous solids- lack a regular 3-D arrangement of atoms (Exs. glass, polymers such as plastic
9/5/12
Phase Changes
12.3 - crystal structures crystalline structure: possess rigid and long-range order; its atoms, molecules, or ions occupy specific positions (Exs. wax ,ice, sugar, salt, diamond, etc.) unit cell: basic repeating structural unit of crystalline solid
-there are seven types of unit cells coordination number: number of atoms surrounding an atom in a crystal lattice
-higher coordination number --> more tightly packed structure
3 types of cubic unit cells: -primitive cubic (sc) c#: 6 -body-centered cubic (bcc) c#: 8 -face-centered cubic (fcc) c#: 12
-a corner atom is shared by eight unit cells
-an edge atom is shared by four unit cells
-a face atom is shared by 2 unit cells
-a central atom is not shared between atoms
# of atoms in structures: sc: 1 atom bcc: 2 atoms fcc: 4 atoms
-atoms such as metals or noble gases are more tightly packed; these are possibly structures: -hexagonal close-packed structure (hcp): -cubic close-packed structure (ccp):
-edge length/radius are related: -sc: a = 2r -bcc: a = 4rt( r )/rt (3) or a = 2.309r -fcc: a = r*rt(8)
X-ray Diffraction: they utilize the scattering of X-rays to determine the structure of an atom
Bragg'sLaw:
12.4- Types of Crystals ionic crystals
-composed of anions/cations
-held together by coulomb forces
-anions are generally bigger than cations
-size and rel. size determines structure covalent crystals
-atoms are held together in an extensive 3-D network entirely by covalent bonds molecular crystals
-the lattice points are occupied by molecules
-attractie forces are dispersion, dipole-dipole, and/or H-bonds metallic crystals
-every lattice point is occupied by an atom of the same metal
-electrons are delocalized over the entire crystal (makes it a good conductor)
-the delocalization keeps the crystal together
12.5- Amorphous Solids amorphous solids- lack a regular 3-D arrangement of atoms (Exs. glass, polymers such as plastic
9/5/12
Phase Changes