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Chemistry - New > Bonding And Shapes Of Molecules > Flashcards

Bonding And Shapes Of Molecules Flashcards

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1
Q

What are intramolecular bonding forces?

A

Forces of attraction between atoms within a molecule

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2
Q

What are intermolecular bonding forces?

A

Forces of attraction between neighbouring molecules

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3
Q

Give examples of intramolecular bonding

A
  • covalent bonding
  • polar covalent bonding
  • ionic
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4
Q

What is covalent bonding?

A

Sharing of or more pairs of electrons between two atoms

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5
Q

What is polar covalent bonding

A

Unequal sharing of one or more pairs of electrons by two atoms

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6
Q

What is ionic bonding?

A

Electrostatic force of attraction between oppositely charged ions

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7
Q

What are weak Van Der Waals forces?

A

Temporary dipoles in molecule attracting/repelling temporary dipoles in next molecule

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8
Q

What are permanent dipole-dipole attractions

A

Permanently polarised molecules attract polarised neighbour, where opposite ends attract

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9
Q

What is hydrogen bonding?

A

Permanently polarised molecules which have hydrogen and one of the elements N, O or F

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10
Q

What is electronegativity?

A

It’s the relative attraction an atom has for shared pairs of electrons in a covalent bond

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11
Q

Use electronegativity values to predict the type of bonding in
phosphine
potassium chloride

A

i) pure covalent
ii) polar covalent

CHART
0 - 0.7 - 1.7

cov - pol cov - ionic

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12
Q

Explain why potassium chloride has a much higher boiling point than phosphine (PH3)

A

Phosphine is held together by weak Van der Waals forces whereas potassium chloride is held together by ionic bonds

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13
Q

Phosphine is virtually insoluble in water, whereas the corresponding hydride of nitrogen which is in the same group as phosphorus is very soluble in water, how so?

A

The corresponding hydride is NH3, which contains a lone pair making the whole molecule polar covalent [electronegative differences]
This results in bonding with water and therefore dissolves in water
Phosphine is non polar and has little/no attraction to the water

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14
Q

What is water of crystallisation?

A

It’s water chemically combined in definite proportions in a crystalline compound

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15
Q

Give two uses of noble gases

A

Helium - in blimps

Argon - in light bulbs

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16
Q

What is the octet rule?

A

Atoms on reaction tend to reach an electronic arrangement with eight electrons in their outermost shell

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17
Q

What are the exceptions to the octet rule?

A

Beryllium and Boron - few electrons in their outer levels so they cannot gain enough electrons to reach eight
D block elements

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18
Q

What is valency?

A

Number of bonds an atom of an element forms when it reacts

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19
Q

What group of elements have variable Valencies and give an example

A

Transition elements

Iron - 2,3,6
Copper - 1,2

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20
Q

What do metal atoms become when they lose one or more electrons?

A

Positively charged - Cation

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21
Q

How is a cation smaller than the corresponding atom?

A

It has lost electrons and is positively charged and therefore lost a shell

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22
Q

Characteristics of Ionic Substances

A

Form crystal lattices
High melting and boiling points due to strong forces of attraction
Polar
Soluble in water
Conduct electricity in molten/aqueous state

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23
Q

Give examples of ionic materials in everyday life

A

Salt tablets - to replace salt lost in sweating

Brine - curing bacon

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24
Q

What factors dictate the extent to which the shared electrons are attracted by different nuclei?

A

Size of the Atom - smaller atom have a stronger attraction because they can get closer to electrons
Nuclear charge - atoms with bigger nuclear charge will have greater attraction for the shared electrons

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25
Q

Characteristics of Covalent Bonding

A

Low melting and boiling points - gases at room temperature due to weak intermolecular forces
Do not conduct electricity due to the fact they consist of neutral molecules
Do not dissolve readily in water

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26
Q

Give examples of polar materials in every day life

A

Water - washing clothes

Glucose - lucozade

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27
Q

Give examples of non - polar materials in every day life

A

Petrol

Cooking oil

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28
Q

Account for the general trend of electronegativity across a period

A

Increases

  • nuclear charge inc, positive attractive force on electrons
  • atomic radius decreases as electrons are pulled in more tightly
  • no screening
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29
Q

Account for the general trend of electronegativity down a group

A
  • extra levels means there is extra screening

- atomic radius inc caused by extra energy levels means electrons aren’t as tightly held and no attracted as strongly

30
Q

Distinguish between a sigma and a pi covalent bond

A

Sigma - end on overlap of orbitals

Pi - sideway overlap of p orbitals

31
Q

What does the electron repulsion theory state?

A

Electron pairs in outer shell of central atom repel each other and end up as far apart as is geometrically possible
Lone pairs have a greater repelling effect than bonding pairs

32
Q

What are the posible shapes sit molecules of general formula : AB2

A

Valency = 2
2 bonds
Linear, V-shaped

33
Q

Account for the difference in shape of NH3 and BF3

A

Draw out
NH3 - three bond pairs and one lone pair
BF3 - three bond pairs

34
Q

Describe the bonding in the nitrogen molecule in terms of sigma and pi bonding

A 
Sigma = 1
Pi = 2
35
Q

What type of intermolecular forces would you expect to find in nitrogen gas? Explain your answer

A

Van Der Waals, it is non polar

36
Q

If a molecule contains two bonds, what shapes can it be?

A

No lone pairs - Linear

Lone pairs - V-shaped

37
Q

If a molecule contains three bonds, what shapes can it be?

A

No lone pairs - Trigonal Planar

Lone pairs - Pyramidal

38
Q

If a molecule contains four bonds, what shapes can it be?

A

Lone pairs - Tetrahedral

39
Q

What bond angle does linear have?

A

180

40
Q

What bond angle does v shape planar have?

A

104.4

41
Q

What bond angle does trigonal planar have?

A

120

42
Q

What bond angle does pyramidal have?

A

107.3

43
Q

What bond angle does tetrahedral have?

A

109.5

44
Q

Identify in ammonia, the type of intermolecular bonding and intermolecular forces present

A

Intramolecular - polar covalent bonding

Intermolecular - hydrogen bonds

45
Q

What is the molecular formula of benzene

A

C6H6

46
Q

Account for the difference in the shapes of BF3 and NH3 molecule

A

Boron - three bond pairs

Nitrogen - three bond pairs and one lone pair

47
Q

How do you know how many sigma and pi bonds there are?

A

Every element forms only a single covalent bond. That is sigma bond. If there are 3 bonds, one must be covalent and other 2 pi
Look at valency to see how many bonds

48
Q

What is bond energy?

A

Its the average energy required to break a bond and seperate atoms in gaseous state

49
Q

The boiling points of hydrogen and oxygen are 20.0K and 90.2K. Account for the higher boiling point of oxygen

A

Stronger intermolecular forces (dipole-dipole)

50
Q

Which are the non polar bond shapes?

A

Linear, trigonal planar, and tetrahedral.

51
Q

Which are the polar bond shapes?

A

V-shaped and Pyramidal

52
Q 
If the eletronegativy difference is
i) 0-.7
ii).7-1.7
iii) 1.7<
what kind of bonds does it have?
A

i) Covalent (non-polar)
ii) Polar covalent
iii) Ionic

53
Q

Give one property that is affected by the presence of intermolecular bonding?

A

Melting point
Boiling point
Density
Solubility in water

54
Q

Would you expect i) the B-Cl bonds and ii) the BCL3 molecules to be polar or non polar? Justify

A

i) Non-polar -> large e.n difference
ii) Polar -> unequal sharing of electrons between B and Cl is cancelled due to symmetry of the molecule as the centres of positive and negative coincide

55
Q

Indicate on your dots and crosses bonding diagram for chlorine monofluoride any full or partial charges that you would expect to result from the formation of the bond between chlorine and fluorine?
E.N values : Cl (3.0) and Fl (4.0)

A

The atom with greater electronegativity - partial negative
The atom with smaller electronegativity - partial positive
In this case, chlorine is partially positibe and fluorine is partially negative

56
Q

NH3, PH3, AsH3

Which if any of the three hydrides would you expect to have intermolecular hydrogen bonding and justify

A

NH3

Hydorgen is bonded to Nitrogen - small and very electronegative

57
Q

NH3, PH3, AsH3
Suggest a reason why ammonia has the highest boiling point of the three hydrides and phosphine’s boiling point is lower than that of arsine

A

i) Hydrogen bond - strongest of intermolecular forces

ii) Smaller mr

58
Q

How would you know if a compound is water soluble or not?

A

Find electronegativity values and see if nonpolar or polar

59
Q

Account for the difference in bond angle between the two molecules, 107.3 in ammonia and 109.5 in silane

A

Lone pair in ammonia - greater repulsion power than bond pair and pushes bonds closer to form a smaller bond angle

60
Q

Give the reason why a molecule with polar bonds can be non-polar

A

Symmetry of molecule - Centres of positive and negative charges coincide

61
Q

Why do ionic substances conduct electricity when molten or dissolved in water but not in solid state?

A

Molten - ions free to move

Solid - not free, fixed

62
Q

Show that the ammonia molecule has polar covalent bonding

A

The electronegativity difference between N and H show unequal sharing

63
Q

Describe the processes involved when ammonia dissolves in water

A
  • Breaking of hydrogen bonds in water

- Forming of hydrogen bonds between ammonia and water

64
Q

Suggest a reason why the boiling point of ammonia (-33) is significantly lower than that of water (100)

A

Weaker bonding in ammonia (small e.n difference)

65
Q

Draw a diagram illustrating hydrogen bonding in ammonia

A

H H
H N - H N
H H

66
Q

Use your knowledge of intermolecular forces to explain why methane has a very low boiling point

A

very weak intermolecular forces

67
Q

The relative molecular mass of methane is only slightly lower than that of water but the boiling point of water is much higher. Suggest a reason for this

A

much stronger hydrogen bonds between water molecules

68
Q

A thin stream of liquid flows from the burette. A stream of water is deflected towards a positively chargd rod whereas a stream of cyclohexane is undeflected. Account for these observations

A

polarity of water causes attraction to charged rod

non-polarity of cyclohexane means it is not affected by charged rod

69
Q

Explain what would happen in the case of the stream of water if the positively charged rod were replaced by a negatively charged rod

A

stream of water still attracted to rod as molecules (dipoles) arrange themselves with
positive pole towards rod

70
Q

(weakly polar) Would you expect hydrogen sulfide to be soluble in water? Explain your answer

A

Only slightly - weakly polar

71
Q

Describe the bonding in the nitrogen molecule in terms of sigma and pi bonding

A

one sigma and two pi

72
Q

Why will water always be deflected by any charged rod?

A

Because it had a dipole moment i.e the centre of positive charge does not coincide with centre of negative charge

Chemistry - New (27 decks)

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