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Chemistry (Tim) > Intermolecular forces > Flashcards

Intermolecular forces Flashcards

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1
Q

where can you find intermolecular forces?

A

between covalent bonds

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2
Q

where are intramolecular forces?

A

inside each molecule

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3
Q

what are intermolecular forces?

A

the attractions between molecules

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4
Q

3 types of intermolecular forces

A

dipole dipole attraction
Van der waal attraction
hydrogen bonds

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5
Q

strength of Van der waal attraction

A

weakest

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6
Q

strength of dipole dipole attraction

A

medium strength

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7
Q

strength of hydrogen bonds

A

strongest

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8
Q

when does dipole-dipole attraction happen?

A

when a covalent molecule has permanent partial + and partial - charges due to having large electronegativity differences

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9
Q

where do van der waal forces occur

A

do not have dipole moments, non-polar covalent

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10
Q

what causes van der waal forces?

A

flickering dipoles

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11
Q

what causes flickering dipoles

A

due to their random movement within the orbitals, there are small lengths of time when the electrons are not equally shared

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12
Q

what does it mean for a flickering dipole to be ‘on’

A

inducing a temporary dipole

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13
Q

what point in time do van der waal forces occur

A

when the 2 molecules involved are both ‘on’

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14
Q

why does NO boil at much higher than N2

A

because van der waal forces are much weaker than dipole-dipole attraction

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15
Q

why does boiling point increase with Mr in non-polar covalent molecules

A

because the number of van der waal forces increases with Mr

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16
Q

what causes the great strength of polythene?

A

it is due to millions of van der waal forces betwee the parallel molecules

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17
Q

boiling points of hydrogen bonding

A

surprisingly high BP

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18
Q

when does a hydrogen bond occur?

A

when hydrogen in a covalent bond with N,O or F in one molecule AND there is a lone pair of electrons on either N,O or F on another neighbouring molecule

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19
Q

example of hydrogen bonding

A

in water

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20
Q

why are N,O and F significant in hydrogen bonding (2)

A
  1. very high electronegativity values

2. smallest atomic radii

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21
Q

why is Cl not involved in hydrogen bonding

A

atomic radius is too bigh

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22
Q

how much stronger is a covalent bond than a hydrogen bond

A

10 times stronger

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23
Q

where do you find hydrogen bonding between N and O

A

in biology; proteins, DNA etc.

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24
Q

why is ammonia extremely soluble in water?

A

becuase of hydrogen bonding

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25
Q

why does water expand below 4ºC?

A

when water is about the solidify as ice, H2O molecules rotate so that they can have their maximum of 4 H bonds, for this they need more “elbow room”

26
Q

why is the boiling point of water much higher than that of NH3 or NF?

A

there is not the maximum aof 4 hydrogen bonds in them as opposed to in water

27
Q

4 properties hydrogen bonding gives water

A

High BP
affects density
skin on water
clustering

28
Q

explain high BP of water

A

very high BP for a its Mr of 18

29
Q

explain how h bonding affects density

A

solid form less dense that liquid form

30
Q

explain the skin of the water

A

water molecules attracted to each other and causes surface tension

31
Q

why does like dissolve like

A

polar solutes dissolve in polar solvents because they are both charged etc.

32
Q

All other things being equal, boiling point increases…

A

boiling point increases with Mr

33
Q

what gives shapes of covalent molecules?

A

Valence Electron Repulsion Theory

34
Q

2 things that the Valence Electron Repulsion Theory states

A

i) Electron pairs repel each other so that they end up as far apart from each other as is possible in space
ii) Lone pairs are better at repelling than bonded pairs

35
Q

why are lone pairs are better at repelling than bonded pairs ?

A

they are closer to the nucleus of the central atom

36
Q

What gives the name of the shape of a molecule?

A

the number of electron pairs (lone or bonded) on the outer shell of the central atom

37
Q

3 steps to determine the shape of a molecule question

A
  1. is it ionic or covalent
  2. draw ring diagram of molecule
  3. count number of electron pairs on the outer shell of the central atom
38
Q

2 electron pairs on outer shell of central atom

A

linear

39
Q

bond angle of linear molecule

A

180º

40
Q

example of linear molecule

A

BeH2

41
Q

3 electron pairs on outer shell of central atom

A

triagonal planar

42
Q

bond angles in triagonal planar molecule

A

120º

43
Q

example of triagonal planar molecule

A

BF3

44
Q

4 bonded electron pairs on outer shell of central atom

A

perfect tetrahedral

45
Q

bond angle of perfect tetrahedral molecule

A

109.5º

46
Q

example of perfect tetrahedral molecule

A

CH4

47
Q

3 bonded and 1 lone pair of electron pairs on outer shell of central atom

A

pyramidal

48
Q

bond angle of pyramidal molecule

A

107º

49
Q

example of pyramidal molecule

A

NH3

50
Q

2 bonded and 2 lone pairs of electrons on outer shell of central atom

A

V-shaped

51
Q

bond angle in v-shaped molecule

A

105º

52
Q

example of v-shaped molecule

A

H2O

53
Q

tetrahedral angle in NH3

A

107º

54
Q

why is tetrahedral angle in NH3 107º?

A

lone pair - bonded pair repulsion is greater than bonded pair - bonded pair repulsion

55
Q

tetrahedral angle in H2O

A

105º

56
Q

why is the tetrahedral angle in H2O 105º?

A

lone pair - lone pair repulsion is greater than lone pair - bonded pair repulsion which is greater than bonded pair - bonded pair repulsion

57
Q

diatomic molecules shape

A

linear

58
Q

3 examples of diatomic molecules

A

H2, O2, N2

59
Q

Shape of carbon with 4 single bonds

A

tetrahedral

60
Q

shape of carbon with one double or triple bond

A

planar

Chemistry (Tim) (8 decks)

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