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C3- BONDING > 3.6- THE SHAPE OF MOLECULES AND IONS > Flashcards

3.6- THE SHAPE OF MOLECULES AND IONS Flashcards

1
Q

What kind of dimension do molecules have?

A

three-dimensional

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2
Q

What sorts of shapes do molecules come in?

A

may different shapes

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3
Q

How do electrons in molecules exist?

A

in pairs in volumes of space called orbitals

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4
Q

What ideas can you use to predict the shape of a simple covalent molecule e.g. one consisting of a central atom surrounded by a number of other atoms? (2)

A

each pair of electrons around an atom will repel all other electron pairs

pairs of electrons will take up positions as far apart as possible to minimise repulsion

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5
Q

What is being able to predict the shape of a simple covalent molecule using ideas: each pair of electrons around an atom will repel all other electron pairs + pairs of electrons will take up positions as far apart as possible to minimise repulsion called?

A

electron pair repulsion theory

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6
Q

How can electron pairs be?

A

be a shared pair or a lone pair

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7
Q

What does the shape of a simple molecule depend on?

A

number of pairs of electrons that surround central atom

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8
Q

What do you need to do first when trying to work out the shape of any molecule?

A

draw a dot-and-cross diagram to find the number of pairs of electrons

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9
Q

What will the shape of the molecule be if there are two pairs of electrons around the central atom?

A

molecule will be linear

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10
Q

What is the furthest away from each other that the two pairs can get? (two pairs of electrons)

A

180°

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11
Q

What is an example of molecule that has two pairs of electrons that surround the atom? (two pairs of electrons)

A

beryllium chloride

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12
Q

When is beryllium chloride covalently bonded molecule? (two pairs of electrons)

A

in the gas phase despite being a metal- non-metal compound

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13
Q

How far apart would they be if there are three pairs of electrons around the central atom?

A

120° apart

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14
Q

What would the shape of the molecule be like if there are three pairs of electrons around the central atom?

A

molecule is planar and is called trigonal planar

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15
Q

What is an example of a molecule that has three pairs of electrons around the central atom?

A

boron trifluoride

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16
Q

If there are four pairs of electrons, when are they the furthest apart?

A

when they are arranged so that they point to the four corners of a tetrahedron

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17
Q

Where is one of the atoms positioned? (four pairs of electrons)

A

at the centre

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18
Q

what is the shape of the molecule with four pairs of electrons?

A

tetrahedral

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19
Q

What is an example of a molecule with four pairs of electrons?

A

methane

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20
Q

Where is the carbon atom of methane situated? (four pairs of electrons)

A

at the centre of the tetrahedron

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21
Q

Where are the hydrogen atoms of methane situated? (four pairs of electrons)

A

at the vertices

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22
Q

What are the angles like? (four pairs of electrons)

A

109.5°

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23
Q

What is the shape of the molecule like with four pairs of electrons?

A

three-dimensional, not planar

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24
Q

As the molecule is not three-dimensional, how does this affect the sum of the angles? (four pairs of electrons)

A

sum of angles can be more than 360°

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25
Q

What ion is tetrahedral?

A

ammonium ion

26
Q

Why is the ammonium ion tetrahedral?

A

four groups of electrons surrounding the nitrogen atom

27
Q

Does the ammonium ion having an overall charge affect the shape?

A

no

28
Q

What is the shape usually when there are five pairs of electrons?

A

trigonal bipyramid

29
Q

What is an example of a molecule with five pairs of electrons?

A

phosphorus pentachloride, PCl5

30
Q

What shape is adopted if there are six pairs of electrons?

A

octahedral

31
Q

What are the bond angles when there are six pairs of electrons?

A

90°

32
Q

What is an example of a molecule with six pairs of electrons?

A

sulphur hexafluoride, SF6

33
Q

what do some molecules have? (hint- electrons)

A

unshared (lone) pairs of electrons

34
Q

What are unshared (lone) pairs of electrons?

A

electrons that are not part of a covalent bond

35
Q

Examples of molecules where lone pairs affect shape? (2)

A

ammonia

water

36
Q

How many pairs of shared and unshared electrons does ammonia have?

A

four pairs of electrons and one of the groups is a lone pair

37
Q

With its four pairs of electrons around the nitrogen atom, what is the shape of the ammonia molecule based on?

A

a tetrahedron

38
Q

As there are only three ‘arms’ in ammonia what is the actual shape of ammonia?

A

triangular pyramid

39
Q

Where are the bonding pairs of electrons attracted towards in ammonia?

A

towards nitrogen nucleus + hydrogen nucleus

40
Q

What is the lone pair of electrons in ammonia attracted by and what happens?

A

attracted only by nitrogen nucleus and so is pulled closer to it than shared pairs

41
Q

As the lone pair on ammonia is pulled closer to the nitrogen than the shared pairs, what is the repulsion like?

A

repulsion between lone pair of electrons + bonding pair of electrons greater than that between two bonding pairs

42
Q

What does the effect of increased repulsion between the lone pair and bonding pairs of electrons in ammonia have?

A

squeezes hydrogen atoms together, reducing all H-N-H angles

43
Q

What is the approximate rule of thumb per lone pair? (hint-an angle)

A

2°

44
Q

What is the bond angles in ammonia approximately?

A

107°

45
Q

How many pairs of electrons are there around the oxygen atom in water?

A

four pairs of electrons

46
Q

What is the shape of water based on?

A

tetrahedron

47
Q

How many ‘arms’ of the tetrahedron are lone pairs that are not part of a bond? (water)

A

two

48
Q

As two of the ‘arms’ of the tetrahedron are lone pairs that are not part of a bond what shape does this result in? (water)

A

V-shaped or angular molecule

49
Q

What shape do the electrons form in water? (same as ammonia)

A

tetrahedron

50
Q

What shape do the bonds form in water?

A

V-shaped

51
Q

What is the H-O-H angle? (water)

A

104.5°

52
Q

What shape does the electrons form in ammonia?

A

tetrahedron

53
Q

What shape do the bonds form in ammonia?

A

triangular pyramid

54
Q

How many bonding pairs and lone pairs are there in chlorine tetrafluoride ion, CLF4-?

A

four bonding pairs

two lone pairs

55
Q

What do one of the lone pairs in chlorine tetrafluoride ion, CLF4- contain?

A

electron that has been donated to it, so charge on ion is negative (-1)

56
Q

How many pairs of electrons are there around the chlorine atom in chlorine tetrafluoride ion, CLF4-?

A

six pairs of electrons

57
Q

What is the shape of chlorine tetrafluoride ion, CLF4- based on?

A

octahedron in which two arms are not part of a bond

58
Q

As lone pairs repel what position do they adopt? (chlorine tetrafluoride ion, CLF4-)

A

adopt a position furthest apart

59
Q

What shape does it leave as the lone pairs adopt a position furthest apart? (chlorine tetrafluoride ion, CLF4-)

A

flat square-shaped ion described as square planar

60
Q

Bonding repulsion from lowest to highest:

A

bonding pair- bonding pair

lone pair- bonding pair

lone pair- lone pair

C3- BONDING (7 decks)

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