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unit 2.5 Flashcards

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1
Q

what does VSEPR stand for

A

valence shell electron pair repulsion

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2
Q

what is the premise of the VSEPR theory

A

because electron pairs in the same valence shell carry the same charge, they repel each other –> spreads apart as far as possible

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3
Q

“rules” of the VSEPR theory

A
  • 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
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4
Q

central atom with 2BP/0LP- electron group arrangement + angles

A

linear, 180 degrees b/w electrons

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5
Q

central atom with 3BP/0LP- electron group arrangement + angles

A

trigonal planar, 120 degrees

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6
Q

central atom with 2BP/1LP- electron group arrangement + angles

A

bent, <120 degrees

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7
Q

central atom with 4BP/0LP- electron group arrangement + angles

A

tetrahedral, 109.5 degrees

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8
Q

central atom with 3BP/1LP- electron group arrangement + angles

A

trigonal pyramidal, <109.5 degrees (107.5)

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9
Q

central atom with 2BP/2LP- electron group arrangement + angles

A

bent/v-shaped, «109.5 degrees (104.5)

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10
Q

central atom with 5BP/0LP- electron group arrangement + shape

A

trigonal bipyramidal, trigonal planar and extra e added to top and bottom

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11
Q

central atom with 4BP/1LP- electron group arrangement + shape

A

seesaw, trigonal planar with one e removed and extra e added to top and bottom

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12
Q

central atom with 3BP/2LP- electron group arrangement + shape

A

T-shaped, 2 vertical e one horizontal e

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13
Q

central atom with 2BP/3LP- electron group arrangement + angles

A

linear, 180 degrees

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14
Q

central atom with 6BP/0LP- electron group arrangement + shape

A

octahedral, 4 e on horizontal plane and 2 e on vertical plane

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15
Q

central atom with 5BP/1LP- electron group arrangement + shape

A

square-based pyramid, 3e on horizontal plane and 2 e on vertical plane

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16
Q

central atom with 4BP/2LP- electron group arrangement + shape

A

square planar, 2e on horizontal plane and 2 e on vertical plane

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17
Q

central atom with 3BP/3LP- electron group arrangement + shape

A

T-shaped, 1 e on horizontal plane, 2 e on vertical plane

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18
Q

central atom with 2BP/4LP- electron group arrangement + angles

A

linear, 180 degrees

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19
Q

what is the valence bond theory

A

theory that covalent bonds are formed when atomic orbitals on neighbouring atoms overlap
- the greater the overlap, the stronger the bond

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20
Q

how is a sigma bond formed

A
  • end to end overlap of atomic orbitals
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21
Q

characteristics of a sigma bond

A
  • forms single bonds
  • electron density is concentrated b/w nuclei of bonded atoms
  • allows for free rotation of atoms
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22
Q

how is a pi bond formed

A
  • side to side overlap of atomic orbitals
  • requires a formed sigma bond
  • can only form double bonds b/w atoms in same plane
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23
Q

characteristics of a pi bond

A
  • 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
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24
Q

what is hybridization

A
  • mixing or blending of s,p and sometimes d orbitals to form hybrid orbitals
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25
Q

what are hybrid orbitals used for

A
  • can overlap with orbitals on other atoms to make bonds, or accommodate nonbonding pairs
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26
Q

an atom with a lower/higher electronegativity has a stronger attraction for shared electron pairs

A

higher

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27
Q

in a polar molecule, what are the two sides called

A

electron rich and electron deficient

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28
Q

what kind of bond does molecule polarity create

A

polar covalent

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29
Q

what is the size of a dipole measured by

A

dipole moment

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30
Q

formula for dipole moment

A

dipole moment = q (separated charge) x r (distance between)

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31
Q

when do polar covalent bonds not lead to polar molecules

A

when the net dipole moment is 0
- when a molecule has dipole that cancel out each other

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32
Q

how to determine molecular polarity

A
  • draw VSEPR 3D structure
  • assign partial charges/dipoles
  • determine net dipole
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33
Q

examples of intramolecular forces and what they are responsible for

A

ionic bonds, covalent bonds, metallic bonds –> chemical bonding and chemical properties

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34
Q

examples of intermolecular forces and what they are responsible for

A

london dispersion force, dipole-dipole, hydrogen bonds –> physical properties of a substance (volatility, solubility, conductivity)

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35
Q

are intramolecular or intermolecular forces stronger

A

intramolecular

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36
Q

where can london dispersion forces be found and how do they occur

A
  • 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
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37
Q

what determines amount of london dispersion forces between atoms

A
  • more e = more london dispersion forces (more significant polarity)
  • more SA = more london dispersion forces (increases likelihood on instantaneous dipole)
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38
Q

what are dipole-dipole forces, how they they occur

A
  • attraction between 2 polar molecules
  • strength depends on EN values
  • medium strength force
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39
Q

what force is responsible for “like dissolves like”

A

dipole-dipole forces

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40
Q

what is hydrogen bonding, where and how does it occur

A
  • a very strong dipole-dipole attraction
  • occurs between H and a very EN element (F,O, N)
  • must need large EN difference to occur
41
Q

why does hydrogen bonded with F,O,N have such a higher BP than when bonded with other atoms?

A

a hydrogen bond is present instead of a regular dipole-dipole force therefore needing more energy to break the stronger bonds

42
Q

what forces are present in non-polar molecules

A

london dispersion forces

43
Q

what forces are present in polar molecules

A

london dispersion and dipole dipole forces

44
Q

what forces are present in polar molecules with H

A

london dispersion, dipole-dipole, and hydrogen bonding

45
Q

importance of water’s maximum density at 4C

A
  • prevents freezing up in lakes
46
Q

importance of water’s abnormally high MP and BP

A

permits water to exist as liquid on earth’s surface

47
Q

importance of water’s high heat capacity (2nd to ammonia)

A

moderates temperatures bye preventing extremes

48
Q

importance of water having one of highest known heat of vaporization

A

to heat transfer in atmosphere and ocean while moderating temperature extremes

49
Q

importance of water’s high surface tension

A

regulates drop formation in clouds and rain

50
Q

importance of water’s ability to absorb radiation

A

controls biological activity in bodies of water and controls atmospheric temperature

51
Q

importance of water’s ability to be a universal solvent

A

aides in transfer of dissolved substances in hydrological cycle and biological systems

52
Q

what are the 2 types of covalent structures

A

covalent network, molecular covalent

53
Q

what are properties of molecular covalent substances determined by

A

intermolecular forces

54
Q

what are properties of covalent network substances determined by

A

lattice features

55
Q

volatility in substances with a covalent network structure

A
  • 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
56
Q

volatility in substance with a molecular covalent structure

A
  • 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
57
Q

what makes a substance with a molecular covalent structure more/less volatile

A
  • larger molecules have lower volatility + higher MP, BP because of stronger LDF compared to smaller molecules
58
Q

electrical conductivity in substances with molecular covalent structure and most substances with covalent network

A
  • poor conductor because electrons are “locked” into covalent bonds and do not contain ions
59
Q

exceptions to the poorly conductive substances with covalent network

A

graphite + graphene (has presence of delocalized e)
silicon (a semi-conductor)

60
Q

difference b/w graphite and graphene

A

graphene is a single layer of carbon atoms arranged in hexagonal lattice while graphite is multiple layers of graphene

61
Q

solubility in substances with a molecular covalent structure

A
  • soluble when forces b/w solute-solvent are greater than b/w solute-solute
62
Q

solubility in substance with a covalent network structure

A
  • insoluble in most solvents because of the strong covalent bonds b/w atoms
63
Q

alcohols soluble/insoluble in water, why?

A

soluble
- able to form hydrogen bonds meaning more likely to dissolve in water

64
Q

solubility of primary alcohols decrease/increase with increasing carbon lengths

A

decrease

65
Q

hydrocarbon chains/oils are soluble/insoluble in water, why?

A

insoluble
- are non-polar and therefore cannot mix due to different polarities

66
Q

how does soap clean grease

A
  • 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
67
Q

what is chromatography

A

how components of a mixture can be separated and identified

68
Q

what does chromatography need to involve

A

a mobile phase and a stationary phase

69
Q

stationary phase and mobile phase of paper chromatography

A

stationary: rectangular piece of chromatography paper
mobile: solvent

70
Q

how does paper chromatography work

A
  • 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)
71
Q

how can results of paper chromatography be changed

A

using different solvents of different polarities

72
Q

what is thin layer chromatography (TLC)

A
  • same idea as paper chromatography but greater sensitivity and more expensive
73
Q

stationary and mobile phase of thin layer chromatography

A

stationary: glass/metal rectangular plate coated with silica/alumina (very polar substances)
mobile phase: non-polar organic solvenet

74
Q

how does thin layer chromatography work

A
  • 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
75
Q

what is the retardation factor

A
  • quantifies results of chromatography
  • ration of distance travelled by spot to distance travelled by solvent
76
Q

what can solute distance travelled in chromatography by affected by

A

pH, temperature, solvent used, paper used

77
Q

what is the retardation factor used for

A

identify substances by comparing experimental values to widely accepted values

78
Q

brief summary of liquid column chromatography

A
  1. sample put on top of column packed with adsorbant SiO2
  2. solvent poured down column
  3. different components in sample separate into bands in the SiO2
79
Q

brief summary of gas-liquid chromatography

A
  1. carrier gas moves through capillary tube with liquid-coated walls located in heated chamber
  2. sample injected into tube near start
  3. gas+sample moves through tube into detector to the recorder
80
Q

physical properties of non-polar molecular solids, why?

A

soft, low MP, poor conductivity
- held tgt by london dispersion forces (very weaK)

81
Q

physical properties of polar molecule solids, why?

A

low/mod BP+MP, harder crystal, greater solubility in water
- IMFs are stronger than non-polar molecular solids (dipole-dipole + hydrogen bonding)

82
Q

physical properties of giant covalent/network covalent solids, why?

A

high MP+BP, insoluble in water, poor conductors, ranges from hard(most) to soft
- large number of strong covalent bonds hold atoms together

83
Q

allotrope meaning

A

different forms of the same element in the same physical state

84
Q

structure of diamond

A
  • tetrahedral, sp3 hybridization
  • each C bonded to 4 other C
  • no intermolecular forces , only strong covalent bonds
  • C atoms packed closely
85
Q

physical properties of diamond

A

poor electrical conductor, good thermal conductor, brittle, high MP, lustrous when polished

86
Q

structure of graphene

A
  • C atoms bonded to 3 other C atoms in a layer
  • sp2 hybridization
  • hexagonal sheets
  • has delocalized electrons
87
Q

physical properties of graphite

A
  • good electrical conductor
  • layers split easily due to very weak london dispersion forces b/w layers
  • hard to split within each layer
88
Q

structure of nanotube

A
  • can be thought of as graphene rolled into a cylinder
  • extremely thin (1/50000th width of hair) but can be many mm long
89
Q

physical properties of nanotubes

A
  • one of stiffest and strongest fibres known
  • range of thermal, electrical, structural properties that depend on kind of nanotube
90
Q

structure + physical properties of buckminster fullerene (buckyballs)

A
  • C60 (made of 6-C and 5-C rings)
  • sp2 hybridization
  • semi-conductor
91
Q

structure of graphene

A
  • open version of buckyballs or one layer of graphite
  • chicken wire/honeycomb look
  • sp2 hybridization (delocalized e)
92
Q

physical properties of graphene

A
  • lightest/strongest material
  • very good electrical conductor
93
Q

structure of silicon dioxide (SiO2) (quartz/silica)

A
  • 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
94
Q

physical properties of silicon dioxide (SiO2) (quartz/silica)

A
  • strong, insoluble in water, high MP, poor conductor
95
Q

what is amorphous silica known as

A

glass

96
Q

what is crystalline silica known as

A

quartz

97
Q

what are crystalline solids

A

have components that are arranged uniformly

98
Q

what are amorphous solids

A

have components that are arranged randomly

hl chemistry (4 decks)

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