ch 16 Flashcards
polar molecules must have what features
polar bond –> difference in electronegativity (0.5-1.9) draw dipole arrow with bar on less EN side
net dipole –> polar bonds don’t cancel out (not equal and opposite)
water’s properties
- less dense as solid than liquid (freezing expands)
- high boiling point
- liquid at room temp unlike molecules with similar mass
intermolecular forces
and give the names
attractive forces BETWEEN molecules
London Dispersion Force
dipole-dipole
hydrogen bonding
london dispersion force
in all atoms
results from an instantaneous dipole (electron fluctuations e-density)
strength = weak but increases with MM
dipole - dipole
in polar molecules
results from permanent dipoles
strength = moderate/ stronger than LDF
hydrogen bonding
special case of dipole-dipole
H bond to F,O,N
strength = strongest IMF but weaker than bond
intermolecular forces are responsible for:
surface tension
viscosity
capillary action
more forces we have = higher boiling point
two types of solids
amorphous and crystalline
amorphous
disordered structure
ex. plsatic bad
crystalline
ordered, repeating structure
ex. lattice : 3D army of atoms
smallest repeating unit - unit cell
ionic, molecular, atomic
ionic crystalline solid
made from ions
ex. NaCl
molecular crystalline solid
made of molecules
ex. H2O (ice)
atomic crystalline solid
made of atoms
ex: C diamond
2d unit cell
look for smallest repeating unit
simple cubic
unit cell –> lattice –> space-filling unit cell
each corner - 1/8 atom
body-centered cubic
in space filling unit cell, atoms touch along body-diagonal of the cube
1/8 each corner *8 corners = 1
1 in body so 2 total atoms within each cell
same atom in body and corners
face-centered cubic
1/2 atom on face of unit cell
corners 1/8 * 8 = 1 atom
faces 1/2 * 6 = 3 atoms
4 atoms within unit cell
calculating density of FCC unit cell
D = mass/volume
cubic = (edge)^3
edge = r* sqrt8
v = edge^3
4 atoms
calculating density of BCC unit cell
D = mass/volume
cubic = (edge)^3
edge = 4/sqrt3 * r
v = edge^3
2 atoms
close packing
atoms pack together as close as possible
types of close packing
abab - hexagonal close packed (hexagonal unit cell)
2. abca - cubic close packed (FCC unit cell)
3. ionic solids (unit cell reflects stoich. )
^ usually larger anions close pack and smaller cations sit in holes
semiconductors
insulators and conductors
MO theory
close-spaced orbitals
all orbitals included
delta E = change in energy between e- filled MO’s and unfilled MO’s
if delta E is small…
if large…
if intermediate ..
small = conductor
large = insulator
intermediate = semiconductor
if you have a semiconductor you can enhance electrical properties by
adding e- –> n type
adding holes –> p type (give e- places to jump to)
vapor pressure
pressure of gas above liquid or solid
if vaporization happens easily = volatile
doesn’t happen easily = nonvolatile
when do you get the boiling point
when VP = external pressure
1 atm
