Chem 202 Notes

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* 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 & Diagram
Phase- homogenous part of a system that is separated front eh system by a well defined boundary. Phase change- transition from one phase to another
Caused by the removal or Addition of energy or pressure
Boiling point- when the vapor pressure equals the atmospheric pressure. Molar heat of vaporization- amount of heat needed to vaporize a mole of substance at its boiling point. Freezing- transformation of a solid form liquid

Reverse process is called melting or fusion
Melting point- the temperature at which solid and liquid phase exist at the same time. (Dynamic Equilibrium is between melting and freezing) Molar heat of fusion- the energy needed to melt one mole of a solid Sublimation- the press by which a molecule goes directly from the solid phase to the vapor phase. Deposition is the reverse process of sublimation.

Molar enthalpy of sublimation- the energy required to sublime one mole of substance. Additive of Hvap and Hfus
Phase diagram- Sumerians the inductions at which a substance exists ini each phase Phase boundary- a line separating any two region
Triple point- the only combination of pressure and temperature at which all three phases of a substance can exist. Critical temperature- the temp at which a substance can only exist as a fluid no matter how much pressure is entered. Both phases exhibit the same properties.

Chapter 13: physical properties of solutions

13.1 – Types of Solutions
solution: homogeneous mixture of two or more substances
-solutions can be classified by the amount of solute dissolved unsaturated solution: one that contains less solute than the solvent has the capacity to dissolved in a solvent at a specific temp saturated solution: one that contains the maximum mount of solute that will dissolve in a solvent at a specific temperature supersaturated solutions are generally unstable

13.2 – The solution Process
solvation: occurs when the solute molecules are separated from one another and surrounded by solvent...
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