STRUCTURE AND BONDING Flashcards
(26 cards)
Between molecules
intermolecular
Inside molecules
intramolecular
bonding continuum
varying degrees of ionic character
Pure covalent
shared pair electrons to achieve stable outer arrangement
same electronegativities - no ionic character at all
pure covalent example
diatomic elements
Polar covalent
One more electronegative - becomes slightly negative and other slightly positive
Ionic Bonds
Uneven sharing of bonding electrons with large electronegativity difference
Usually, but not always metal and non-metal (sodium chloride)
Pulls electrons towards itself completely, gaining electric and forming negative ion, and other is positive ion
Electrostatic force of attraction between metal ion and non-metal ion.
Arranged into 3d ionic lattice of pos and neg ions
Intermolecular bonds
Van der Waals
LDF
PDP
Hydrogen
LDF
weakest - exists between all atoms and molecules
uneven distribution of electrons within an atom. Results in slightly neg charge and slight pos on either side of atom - temporary dipole established
opposite charges then attract each other
How do we know LDF are between all atoms and molecules
Molecular elements and monatomic elements will condense forming solids if cooled to sufficiently low temperatures - shows must be attraction that is being overcome
Strength of LDF
Higher the larger the atom - more electrons so more dipoles established
Permanent dipole interactions
POLAR
Polar molecules display attractions between opposite charged ends of molecules
Hydrogen bonding
Strongest
Specific type of permanent dipole to permanent dipole attraction that occurs when a hydrogen atom is covalently bonded to a highly electronegative element such as nitrogen, oxygen or fluorine.
Opposite charged ends attracted
examples of hydrogen bonds in molecules
Water, ammonia, alcohols and alkanoic acids
Polarity
A substance which contains polar covalent bonds may not be overall polar due to SHAPE
Water polarity
Water molecules are polar - due to non symmetrical shape molecule is polar (neg and pos side(o- h+))
non-symmetrical
polar
symmetrical example
carbon tetrachloride - non polar
Properties ionic lattice
High mp/bp
conduct when molten or in solution as ions free to move
how can ionic lattice be broken down
electryolisis
properties covalent network
v high mp/mp
hard and do not conduct
properties covalent molecular
low mp/bp
do not conduct some have higher mp than expected - because of intermolecular bond present
Ethanol 79 degrees and Ether -23 degrees- same molecular formula
Same molecular formula
large difference in bp
due to ethanol containing H bonding
Ether is symmetrical so even though contains polar bonds, overall non polar and only bonds present will be LDF
Properties of water
due to hydrogen bonding
density of ice less - water expanding when frozen because hydrogen forming open lattice
high surface tension
relatively high viscosity
