unit 2.5 Flashcards
what does VSEPR stand for
valence shell electron pair repulsion
what is the premise of the VSEPR theory
because electron pairs in the same valence shell carry the same charge, they repel each other –> spreads apart as far as possible
“rules” of the VSEPR theory
- treat all electron pairs/domains as negative charge clouds which repel each other
- only the valence shell electrons of the central atom is important for shape
- repulsion applies to electron domains
- electron pairs must have max. distance apart
- LP takes up more space that BP
central atom with 2BP/0LP- electron group arrangement + angles
linear, 180 degrees b/w electrons
central atom with 3BP/0LP- electron group arrangement + angles
trigonal planar, 120 degrees
central atom with 2BP/1LP- electron group arrangement + angles
bent, <120 degrees
central atom with 4BP/0LP- electron group arrangement + angles
tetrahedral, 109.5 degrees
central atom with 3BP/1LP- electron group arrangement + angles
trigonal pyramidal, <109.5 degrees (107.5)
central atom with 2BP/2LP- electron group arrangement + angles
bent/v-shaped, «109.5 degrees (104.5)
central atom with 5BP/0LP- electron group arrangement + shape
trigonal bipyramidal, trigonal planar and extra e added to top and bottom
central atom with 4BP/1LP- electron group arrangement + shape
seesaw, trigonal planar with one e removed and extra e added to top and bottom
central atom with 3BP/2LP- electron group arrangement + shape
T-shaped, 2 vertical e one horizontal e
central atom with 2BP/3LP- electron group arrangement + angles
linear, 180 degrees
central atom with 6BP/0LP- electron group arrangement + shape
octahedral, 4 e on horizontal plane and 2 e on vertical plane
central atom with 5BP/1LP- electron group arrangement + shape
square-based pyramid, 3e on horizontal plane and 2 e on vertical plane
central atom with 4BP/2LP- electron group arrangement + shape
square planar, 2e on horizontal plane and 2 e on vertical plane
central atom with 3BP/3LP- electron group arrangement + shape
T-shaped, 1 e on horizontal plane, 2 e on vertical plane
central atom with 2BP/4LP- electron group arrangement + angles
linear, 180 degrees
what is the valence bond theory
theory that covalent bonds are formed when atomic orbitals on neighbouring atoms overlap
- the greater the overlap, the stronger the bond
how is a sigma bond formed
- end to end overlap of atomic orbitals
characteristics of a sigma bond
- forms single bonds
- electron density is concentrated b/w nuclei of bonded atoms
- allows for free rotation of atoms
how is a pi bond formed
- side to side overlap of atomic orbitals
- requires a formed sigma bond
- can only form double bonds b/w atoms in same plane
characteristics of a pi bond
- electron density is concentrated above and below plane of nuclei of bonded atoms
- forms double and triple bonds
- does not allow for free rotation of atoms
what is hybridization
- mixing or blending of s,p and sometimes d orbitals to form hybrid orbitals
what are hybrid orbitals used for
- can overlap with orbitals on other atoms to make bonds, or accommodate nonbonding pairs
an atom with a lower/higher electronegativity has a stronger attraction for shared electron pairs
higher
in a polar molecule, what are the two sides called
electron rich and electron deficient
what kind of bond does molecule polarity create
polar covalent
what is the size of a dipole measured by
dipole moment
formula for dipole moment
dipole moment = q (separated charge) x r (distance between)
when do polar covalent bonds not lead to polar molecules
when the net dipole moment is 0
- when a molecule has dipole that cancel out each other
how to determine molecular polarity
- draw VSEPR 3D structure
- assign partial charges/dipoles
- determine net dipole
examples of intramolecular forces and what they are responsible for
ionic bonds, covalent bonds, metallic bonds –> chemical bonding and chemical properties
examples of intermolecular forces and what they are responsible for
london dispersion force, dipole-dipole, hydrogen bonds –> physical properties of a substance (volatility, solubility, conductivity)
are intramolecular or intermolecular forces stronger
intramolecular
where can london dispersion forces be found and how do they occur
- exists between all particles
- occur due to formation of temporary instantaneous dipoles caused by electrons
- one temp dipole induces another dipole in another molecule to get temp dipole attraction
what determines amount of london dispersion forces between atoms
- more e = more london dispersion forces (more significant polarity)
- more SA = more london dispersion forces (increases likelihood on instantaneous dipole)
what are dipole-dipole forces, how they they occur
- attraction between 2 polar molecules
- strength depends on EN values
- medium strength force
what force is responsible for “like dissolves like”
dipole-dipole forces
what is hydrogen bonding, where and how does it occur
- a very strong dipole-dipole attraction
- occurs between H and a very EN element (F,O, N)
- must need large EN difference to occur
why does hydrogen bonded with F,O,N have such a higher BP than when bonded with other atoms?
a hydrogen bond is present instead of a regular dipole-dipole force therefore needing more energy to break the stronger bonds
what forces are present in non-polar molecules
london dispersion forces
what forces are present in polar molecules
london dispersion and dipole dipole forces
what forces are present in polar molecules with H
london dispersion, dipole-dipole, and hydrogen bonding
importance of water’s maximum density at 4C
- prevents freezing up in lakes
importance of water’s abnormally high MP and BP
permits water to exist as liquid on earth’s surface
importance of water’s high heat capacity (2nd to ammonia)
moderates temperatures bye preventing extremes
importance of water having one of highest known heat of vaporization
to heat transfer in atmosphere and ocean while moderating temperature extremes
importance of water’s high surface tension
regulates drop formation in clouds and rain
importance of water’s ability to absorb radiation
controls biological activity in bodies of water and controls atmospheric temperature
importance of water’s ability to be a universal solvent
aides in transfer of dissolved substances in hydrological cycle and biological systems
what are the 2 types of covalent structures
covalent network, molecular covalent
what are the properties of molecular covalent substances determined by
intermolecular forces
what are properties of covalent network substances determined by
lattice features
volatility in substances with a covalent network structure
- solids at room temp and pressure
- non-volatile becuz vaporization needs a lot of energy because of the strong covalent bonds
- very high MP, BP
volatility in substance with a molecular covalent structure
- smaller molecules are gases/liquids at room temp
- generally volatile bcuz vaporization needs less energy bcuz weak IMF
- large variation in volatility bcuz variety of sizes/intermolecular forces
what makes a substance with a molecular covalent structure more/less volatile
- larger molecules have lower volatility + higher MP, BP because of stronger LDF compared to smaller molecules
electrical conductivity in substances with molecular covalent structure and most substances with covalent network
- poor conductor because electrons are “locked” into covalent bonds and do not contain ions
exceptions to the poorly conductive substances with covalent network
graphite + graphene (has presence of delocalized e)
silicon (a semi-conductor)
difference b/w graphite and graphene
graphene is a single layer of carbon atoms arranged in hexagonal lattice while graphite is multiple layers of graphene
when are substances with a molecular covalent structure soluble
- soluble when forces b/w solute-solvent are greater than b/w solute-solute
solubility in substance with a covalent network structure
- insoluble in most solvents because of the strong covalent bonds b/w atoms
alcohols soluble/insoluble in water, why?
soluble
- able to form hydrogen bonds meaning more likely to dissolve in water
solubility of primary alcohols decrease/increase with increasing carbon lengths
decrease
hydrocarbon chains/oils are soluble/insoluble in water, why?
insoluble
- are non-polar and therefore cannot mix due to different polarities
how does soap clean grease
- soap has hydrophobic tail and hydrophilic head
- can interact with both the water and oils at the same time
- forces between hydrophilic head and water pull oil apart
what is chromatography
how components of a mixture can be separated and identified
what does chromatography need to involve
a mobile phase and a stationary phase
stationary phase and mobile phase of paper chromatography
stationary: rectangular piece of chromatography paper
mobile: solvent
how does paper chromatography work
- chromatography paper made of hydrated cellulose, contains many OH groups <– very polar + attracts water
- mixture components divide b/w water layer on paper and solvent on surface of paper
- when using a less polar solvent, less polar components travel more (dissolves on solvent travelling above paper) and polar components travel less (attracted to water in paper)
how can results of paper chromatography be changed
using different solvents of different polarities
what is thin layer chromatography (TLC)
- same idea as paper chromatography but greater sensitivity and more expensive
stationary and mobile phase of thin layer chromatography
stationary: glass/metal rectangular plate coated with silica/alumina (very polar substances)
mobile phase: non-polar organic solvenet
how does thin layer chromatography work
- polar components will travel less as they’re adsorbed into silica/alumina
- non-polar components will travel more as they’re dissolved into non-polar solvent
what is the retardation factor
- quantifies results of chromatography
- ration of distance travelled by spot to distance travelled by solvent
what can solute distance travelled in chromatography by affected by
pH, temperature, solvent used, paper used
what is the retardation factor used for
identify substances by comparing experimental values to widely accepted values
brief summary of liquid column chromatography
- sample put on top of column packed with adsorbant SiO2
- solvent poured down column
- different components in sample separate into bands in the SiO2
brief summary of gas-liquid chromatography
- carrier gas moves through capillary tube with liquid-coated walls located in heated chamber
- sample injected into tube near start
- gas+sample moves through tube into detector to the recorder
physical properties of non-polar molecular solids, why?
soft, low MP, poor conductivity
- held tgt by london dispersion forces (very weaK)
physical properties of polar molecule solids, why?
low/mod BP+MP, harder crystal, greater solubility in water
- IMFs are stronger than non-polar molecular solids (dipole-dipole + hydrogen bonding)
physical properties of giant covalent/network covalent solids, why?
high MP+BP, insoluble in water, poor conductors, ranges from hard(most) to soft
- large number of strong covalent bonds hold atoms together
allotrope meaning
different forms of the same element in the same physical state
structure of diamond
- tetrahedral, sp3 hybridization
- each C bonded to 4 other C
- no intermolecular forces , only strong covalent bonds
- C atoms packed closely
physical properties of diamond
poor electrical conductor, good thermal conductor, brittle, high MP, lustrous when polished
structure of graphene
- C atoms bonded to 3 other C atoms in a layer
- sp2 hybridization
- hexagonal sheets
- has delocalized electrons
physical properties of graphite
- good electrical conductor
- layers split easily due to very weak london dispersion forces b/w layers
- hard to split within each layer
structure of nanotube
- can be thought of as graphene rolled into a cylinder
- extremely thin (1/50000th width of hair) but can be many mm long
physical properties of nanotubes
- one of stiffest and strongest fibres known
- range of thermal, electrical, structural properties that depend on kind of nanotube
structure + physical properties of buckminster fullerene (buckyballs)
- C60 (made of 6-C and 5-C rings)
- sp2 hybridization
- semi-conductor
structure of graphene
- open version of buckyballs or one layer of graphite
- chicken wire/honeycomb look
- sp2 hybridization (delocalized e)
physical properties of graphene
- lightest/strongest material
- very good electrical conductor
structure of silicon dioxide (SiO2) (quartz/silica)
- forms giant covalent structure w/ tetrahedral arrangement
- each Si covalently bonds to 4 O
- each O covalently bonds to 2 Si
- each O atoms “forms bridge” between each Si
physical properties of silicon dioxide (SiO2) (quartz/silica)
- strong, insoluble in water, high MP, poor conductor
what is amorphous silica known as
glass
what is crystalline silica known as
quartz
what are crystalline solids
have components that are arranged uniformly
what are amorphous solids
have components that are arranged randomly
