how molecules stick together Flashcards
how do molecules have linear shapes
if bonding pairs are in negative charge cloud because electrons repel each other and move away from each other as far as possible
shapes of molecules with 2 electron pairs
linear shape
bond angle
angle between 2 bonds to identify same shaped molecules
bond angle of linear shapes
180
molecules name and shape and angle with 3 bond pair electrons
-trigonal planar
120 degrees
molecules name and shape with 4 electron pairs
109.5 degrees
tetrahedral
ammonia bond angle
107
bond angle in water
104.5
bond angle when there is lone pair with bond pair
bond angle decreases
why does bond angle decrease with lone pair and bond pair
lone pair charge cloud wider than bond pair charge cloud
-repel more than bonding pairs
-distance between bonding pairs decreases
order of electron pair repulsion biggest to smallest
lone pair lone pair
lone pair bond pair
bond pair bond [air
VESPR
valence electron shell repulsion theory
-predicting shapes of molecules
molecule with 2 bonding pairs and one lone pair
shape is bent
angle 118
molecule with 3 bond pairs and 1 lone pair
shape trigonal pyramidal
bond angle 107
water with 2 bonding pairs and lone pairs shape and angle
-bent
angle 104.5
molecule with 5 electron bonding pairs shape and angle
trigonal bipyrymidal
-120 and 90
molecule with 4 bonding pairs and 1 lone pair
-seesaw FML
-100 and 85
molecule with 3 bonding pairs and 2 lone pairs
t shaped
88 degrees
molecule with 3 bonding pairs and 2 lone pairs shape and angle
linear
180
molecule with 6 bonding electron pairs
-90 degrees
octahedral
molecule with 4 bonding pairs and 2 lone pairs
-lone pairs opposite
-90
-square planar
predicting shape of molecule when electron pairs not given
-electron pairs repel as much as possible
-draw dot and cross
count how many electron pairs bonding and lone
-identify shape
-add atoms and lone pairs
shapes of molecules with double bonds
-double bonds dont repel each other
linear arrangement
-180
how to know if molecule polar
if polar bonds
dipole
so molecule polar
bonds on same side of molecule
what happens if bonds not on same side of molecule
-dipoles cancel oout when following vectors of bond charges
if all atoms around central atom all same polar or not
if all same molecule non polar
if all same and dipoles dont cancel out molecule is polar
dipole dipole forces
when attractive force bwteeen oppoiste charges of molecules is dipole dipole forces
partial charges
how does dipole get stronger
as charge difference increases
when does hydrogen bonding occur
when hydrogen is covalently bonded to nitrogen, oxygen or fluorine
drawing hydrogen bonds
partial charges
lone pairs
draw hydrogen to lone pairs from all water molecules or whatever molecules on a strraight line2 hydrogens to 0 lone pair
hydrogen bonding in water
-large difference in electronegativuty between hydrogen and oxygen
-causes H to have strong positive and O to have strong negative
-strong positive attracts lone pair of O
-neighouring atoms attracted to positive partial charge
temporary dipoles
movement of electrons of non polar molecules means electrons can move and no longer have dipole so dipole temporary
induced dipole
both charges on molecule so molecule with dipole repels electrons on negative side and move across molecule so negative side becomes positive so attracted molecules
van der waal forces
arise when movement of electrons in one molecule creates a temporary dipole
-this induced dipole in a nearby molecule
-results in the attraction between partial charges of nearby molecules
what do all polar molecules have
dipole di[pole forces
van der waal forces
van der waal force strength down a group
fluorine has less electrons than iodine so less likely of even dispersion of electrons as more
stronger charge difference
comparing boiling and melting points
-what bond present
-strength of bonds
why dont molecular liquids and gases conduct electricity
-when heated intermolecular forces weaken but covalent bonds dont break so electrons not free to move between molecules and carry charge
why is ice less dense than water
-hydrogen bonds that hold water molecules move further away from each other to make structure called open lattice structure
macromolecules
large molecules with covalent bonds
lattice made up of macromolecules
called a marcomolecular or giant covalent lattice
what a lattice made up of smaller molecules
molecular lattice
forces between chain marcomolecules
between chains
forces between sheet macromolecules
between sheets
large macromolecules like diamond
covalent bonds
no intermolecular forces
diamond
macromolecular lattice held together by covalent bonds
graphite
marcomolecular lattice bonded to 3 carbons each and graphene sheets held together by weak van der waal forces
allotropes
different structures that can form when atoms of that element bond together
allotropes of carbon
diamond
coal
graphene
graphite
buckminsterfullerene
nanotubes
how does graphite have 3 bonds carbon
p orbital line in sheet how pi overlap sigma bonds
-p overlap strong bonds
like double bonds but not
1 spare electron from p orbital is delocalized
why does diamond not conduct electricity
all of diamonds outer electrons are in covalent bonds so no delocalised electrons
why can graphite conduct electricity
has delocalized electrons so can move freely throughout each layer and carry a charge
hardness comparison of graphite and diamond
diamond very hard - drills
graphite very soft- pencils
melting points of diamond and graphite
very high for both
why does graphite have such a high melting point
have to break covalent bonds as well as intermolecular forces
representing diamond n
C (s)
why are marcomolecukles represented using empiricla formila
number of atoms doesnt effect properties of macromolecule
mettalic bonding
-metallic lattice
-made up of delocalized electrona and cations
-held together by electrostatic forces between cations and delocalized electrons
high melting points
low solubility
-conduct electricity when solid and liquid
malleable
-ductile
ionic bonding
-ionic lattice
cations and anions
held together by electrostatic forces between cations and anions
high melting points
usually high solubility
consustc electricity when dissolved in water
-brittle
molecular lattices covalent bonding
-fewer than 1000 atoms
-intermolecular forces
low melting points
varying solubility
never conducts electricity
giant structures
metallic
ionic
macromoleciar structures
what happens when ionic substances dissolve in water
ions in lattice separate and surrounded by sphere of water molecules
-ions surrounded by water molecules are hydrated ions
ion dipole
when hydrated ions stick to water molecules
water of crystalisation
water molecules woven into salt lattice
representing water of crystalisation
other molecules inlattice with dot and number of water molecules present to show how many per other molecule in lattice and that water regularly in lattice
