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A Level Chemistry > molecular geometry > Flashcards

molecular geometry Flashcards

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1
Q

why is it important that we can predict the shape of molecules?

A

so we know how they interact with each other and other molecules

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2
Q

what are the 2 types of pairs?

A

bonding pairs, lone pairs

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3
Q

why do we assume electron pairs repel each other

A

electrons are negative so the region of space they occupy (orbital) is also negative. like charges repel so electron pairs must be furthest distance away from each other

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4
Q

linear arrangement is…

A

… straight line

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5
Q

2 bonding pairs is a … arrangement

A

linear

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6
Q

what is the bond angle of a linear molecule?

A

180˚

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7
Q

what is the name of a molecule with 3 bonding pairs?

A

trigonal planar

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8
Q

what is the bond angle of a trigonal planar molecule?

A

120˚

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9
Q

how do you draw 3D molecules

A

wedge = towards you
dashed line = away from you

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10
Q

what are the bonding angles of a tetrahedral molecule?

A

109.5˚

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10
Q

what is the name of a molecule with 4 bonding pairs?

A

tetrahedral

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11
Q

as lone pair increase, bond angles…

A

decrease

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12
Q

why do lone pairs repel more than bonding pairs

A

‘charge cloud’ isn’t shared between atoms so it has more freedom to move so is wider.

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13
Q

state VSEPR theory

A

LpLp>LpBp>BpBp

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14
Q

what does VSEPR theory stand for?

A

Valence Shell Electron Pair Repulsion Theory

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15
Q

what is the name of a molecule with 2 bonding pairs and 1 lone pair?

A

bent

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16
Q

what is the bond angle of a bent molecule?

A

118˚

17
Q

what’s the name of a molecule with 3 boning pairs and 1 lone pair?

A

trigonal pyramidal

18
Q

what is the bond angle of a trigonal pyramidal molecule?

A

107˚

19
Q

what is the name of a molecule with 2 lone pairs and 2 bonding pairs?

A

bent - same structure as 1 lone pair and 2 bonding pairs

20
Q

what is the bond angle of a bent molecule (2 Lp)?

A

104.5

20
Q

what is the name of a molecule with 5 bonding pairs?

A

trigonal bipyramidal

21
Q

what are the bond angles for a trigonal bipyramidal molecule?

A

120˚, 90˚

22
Q

why isn’t the bond angle for trigonal bipyramidal 180/5 ∴ 72˚?

A

they should be repelling as far as possible and the only way to do this is to have more than one plane so although they aren’t repelling equally, they’re repelling the max distance

23
Q

what is the name of the molecule with 4 bonding pairs and 1 lone pair?

A

trigonal bipyramidal but known as seesaw/sawhorse

24
Q

what are the bond angles of a seesaw molecule

A

87˚, 102˚

25
Q

what is the name of the molecule with 3 bonding pairs and 2 lone pairs?

A

trigonal bipyramidal/ t-shaped

26
Q

what is the bond angle in a t shaped molecule?

A

88˚

27
Q

what is the name of a molecule that has 2 bonding pairs and 3 lone pairs?

A

//////trigonal bipyramidal atomic shape but linear electron configuration

28
Q

how would you draw an octahedral molecule

A

straight lines above and below. 2 wedges each side bottom half. 2 dashed lines each side coming from top.

29
Q

whats the name of a molecule with 6 bonding pairs?

A

octahedral

30
Q

what is the bonding angle of an octahedral molecule?

A

90˚

31
Q

what is the name of a molecule with 4 bonding pairs and 2 lone pairs?

A

square planar

32
Q

what is the bond angle of a square planar and why is this?

A

still 90˚like octahedral because the lone pairs are positioned top and bottom

33
Q

what assumptions do we make when predicting the shape of a molecule?

A
  • electron pairs repel to be as far apart as possible
  • lone pairs repel more than bonding pairs
34
Q

steps to predict the shape of a molecule

A

1) draw a dot and cross diagram
2) count number of electron pairs around the central atom
3) identify the electron pair arrangement
4) add in atoms and lone pairs

35
Q

what do we assume when predicting the shape of a molecule with double bonds?

A
  • the electron pairs in a double bond don’t repel each other and treat them as one
36
Q

if a molecule has single and double bonds, why doesn’t the double bond cause extra repulsion?

A

double bonds repel a similar amount to single bond as any extra repulsion from pi bonds is cancelled out through sigma bonds as sigma bonds spend equal time above and below the atom

37
Q

when two atoms are a pair of electrons they exist in a … bond?

A

sigma

38
Q

when two atoms share a second pair of electrons they exist in a … bond

A

pi

39
Q

when drawing an ion that has a positive charge, the electron is removed from…

A

… the least electronegative ion

40
Q

when drawing an ion that has a negative charge, we add an electron to the…

A

A Level Chemistry (6 decks)

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