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Organic Chem AS Mock > TOPIC 2: Shapes of Molecules & Intermolecular Forces > Flashcards

TOPIC 2: Shapes of Molecules & Intermolecular Forces Flashcards

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1
Q

2 areas of electron density

A

Linear : 180°

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2
Q

2 areas of electron density w/ 2 lone pairs

A

Non-linear : 104.5°

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3
Q

3 regions of electron density

A

Trigonal planar : 120°

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4
Q

3 regions of electron density w/ 1 lone pair

A

Pyramidal : 107°

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5
Q

4 areas of electron density

A

Tetrahedral - 109.5°

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6
Q

5 areas of electron density

A

Trigonal bipyramidal - 90° & 120°

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7
Q

6 areas of electron density

A

Octahedral - 90°

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8
Q

Wedges: solid line

A

In the paper

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9
Q

Wedges: solid wedge

A

Coming out of paper

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10
Q

Wedges: dotted wedge

A

Going into paper

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11
Q

Electron pair with strongest repulsion

A

Lone pair - lone pair

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12
Q

Electron pair with weakest repulsion

A

Bonding pair - bonding pair

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13
Q

How does a lone pair affect the bond angle

A

Reduces it by 2.5° for each lone pair

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14
Q

Explain the trend of in the melting points of the halogens as you move down group 7 (3)

A
  • melting points increase down group 7
  • greater number of electrons
  • so induced dipole-dipole interactions are stronger
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15
Q

Explain why each bond angle in BH3 is 120° (2)

A
  • boron has 3 bonding pairs of electrons
  • which repel each other equally
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16
Q

Explain how the C-H bond differs from the N-H bond in terms of bond polarity (2)

A
  • N-H bond more polar than C-H
  • as difference in electro negativity between nitrogen and hydrogen atom is larger
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17
Q

Define: electronegativity (2)

A
  • the ability of an atom to attract electrons
  • in a covalent bond
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18
Q

State whether HCONH2 is a polar molecule (3)

A
  • polar
  • because polar bonds present
  • unsymmetrical distribution of charge
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19
Q

What is the meaning of δ+ (1)

A

Partial positive charge

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20
Q

State which property of atoms causes a bond to be polar (1)

A

Electronegativity difference

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21
Q

Which compound isn’t influenced by a lone pair of electrons?

A

BF3

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22
Q

What compound has a shape that is influenced by lone pairs around the central atom?

A

ClF3

23
Q

State how two carbon atoms form a carbon-carbon bond in graphene (1)

A

Shared pair of electrons

24
Q

Empirical formula of graphene

A

CH

25
Q

Explain why a CH2Cl2 molecule is polar (1)

A

The molecule is non-symmetrical

26
Q

Predict and explain shape of the AlH4- ion (3)

A

Shape : tetrahedral

Explanation :
- equal repulsion
- b/w 4 bonding pairs

27
Q

Why does electronegativity increase as you go up the group?

A

Because there’s less shells so less shielding -> electrons are attracted more easily

28
Q

How do lone pairs affect polarity

A

Lone pair:
- non-symmetrical
- polar

No lone pair:
- symmetrical
- non-polar (dipoles cancel out)

29
Q

What molecules are never polar

A

Hydrocarbons

30
Q

Estimate the H-O-H bond angle in water using electron pair repulsion theory (3)

A
  • 104.5°
  • 4 areas of electron density
  • extra repulsion due to lone pairs
31
Q

Suggest a way that the bond angle in NH3 could become 109.5° (3)

A
  • Nitrogen can form a dative bond
  • therefore no longer any lone pairs
  • so no extra repulsion
32
Q

Minimum and maximum number of electrons in outer shell of sulfur (2)

A

Min = 8

Max = 18

33
Q

Predict if the SF6 molecule is polar and explain why. (2)

A
  • non polar
  • no overall dipole
34
Q

Explain why the C-F bond does not readily break (2)

A
  • C-F bond is stronger
  • and more polar
35
Q

Predict and explain if halogens can conduct electricity in any state (2)

A
  • do not conduct in any state
  • as there’s no delocalised electrons
36
Q

Order the three main types of intermolecular forces in ascending order of strength (3)

A
  • induced dipole-dipole
  • permanent dipole-dipole
  • hydrogen bonding
37
Q

Identify the strongest intermolecular force between:

i) methanal molecules
ii) methanoic acid molecules
iii) water and methanal
iv) water and methanoic acid

A

i) permanent dipole-dipole forces

ii) hydrogen bonding

iii) hydrogen bonding

iv) hydrogen bonding

38
Q

Explain why sodium methanoate is solid at room temp and methanoic acid is a liquid (3)

A
  • sodium methanoate is ionic
  • methanoic acid is a simple covalent substance
  • ionic bonds are stronger
39
Q

Explain why the boiling point of H2O does not follow the Group 6 boiling point trend (2)

A
  • water is able to form hydrogen bonds between molecules
  • hydrogen bonds are the strongest intermolecular forces
40
Q

Explain how physical properties of ammonia allow it to be easily separated in the Haber process (2)

A
  • boiling point of ammonia higher than that of hydrogen and nitrogen
  • mixture of gases can be cooled so ammonia condenses first
41
Q

Explain why intermolecular forces between water molecules are stronger than those b/w ammonia molecules (4)

A
  • oxygen has a greater mass
  • so stronger dipole-dipole interactions
  • water can form more hydrogen bonds per molecule than ammonia
  • as there’s 2 lone pairs of electrons on oxygen but only 1 on nitrogen
42
Q

Explain why the bond angle in NH3 is different to that of BH3 (2)

A
  • lone pairs of electrons on N have greater repulsion
  • so pairs of electrons arrange themselves as far apart as possible to minimise repulsion
43
Q

Explain why CCl4 is non-polar but CH3Cl is polar (3)

A
  • C-Cl bond is polar
  • CCl4 is a symmetrical molecule
  • polarity of C-Cl bonds cancel out in CCl4
44
Q

Explain whether B-Cl bond or B-H bond is more polar (4)

A
  • B-Cl = covalent bond
  • formed by shared pair of electrons between B and Cl atom
  • B-H bond less polar than B-Cl bond
  • as difference in electronegativity in B-H is smaller
45
Q

Predict whether the b.p of CH4 is lower than the b.p of CCl4 (4)

A
  • lower than CCl4
  • bcs CCl4 has more electrons
  • therefore stronger London forces in CCl4
  • so more energy required to break intermolecular forces b/w CCl4 molecule
46
Q

Predict whether each is polar or non polar: (3)

OF2
PF3
BCl3

A
  • OF2 = polar
    ➡️ bond polarities DON’T cancel out
  • PF3 = polar
    ➡️ bond polarities DON’T cancel out
  • BCl3 = non-polar
    ➡️ bond polarities DO cancel out
47
Q

Explain why ice has a density lower than liquid water (2)

A
  • water molecules in ice spread further away
  • hydrogen bonding between water molecules causes ice to have this anomalous density
48
Q

Explain why the m.p of water is higher than that of phosphine (3)

A
  • water has hydrogen bonds
  • phosphine has permanent dipole-dipole forces
  • hydrogen bonds require more energy to overcome
49
Q

Compare the bond angles in F-C-F and F-N-F. (5)

A

F-C-F:
- 120°
- due to 3 areas of electron density around carbon

F-N-F:
- 107°
- due to 4 areas of electron density around nitrogen
- extra repulsion from unbonded pairs

50
Q

Explain difference in molecular polarity in tetraflourohydrazine and tetrafluoroethene (4)

A
  • C-F and N-F bonds are both polar
  • but C2F4 is a symmetrical molecule
  • so bond polarity in C2F4 cancels out
  • N2F4 is an unsymmetrical molecule
51
Q

Explain why methanol is soluble in water (3)

A
  • O-H bond = polar
  • methanol can form H-bonds with water
  • H-bonding with water increases solubility
52
Q

Predict whether alkanes are soluble in either water or propanone (5)

A
  • insoluble in water
  • soluble in propanone
  • non-polar molecules
  • dont form h-bonds with water
  • form more London forces w/ propanone
53
Q

Explain why iodine vaporises easily (2)

A
  • weak induced d.p - d.p interactions between molecules
  • these weak forces are easily overcome
54
Q

Explain the difference in electrical conductivity of sodium chloride and iodine (3)

A
  • iodine has no free electrons to carry charge
  • molten NaCl has ions which are free to move
  • solid NaCl has no free ions as they’re fixed in position therefore NaCl cannot conduct when solid

Organic Chem AS Mock (3 decks)

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