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Flashcards in Bonding And Shapes Of Molecules Deck (72):
1

What are intramolecular bonding forces?

Forces of attraction between atoms within a molecule

2

What are intermolecular bonding forces?

Forces of attraction between neighbouring molecules

3

Give examples of intramolecular bonding

-covalent bonding
-polar covalent bonding
-ionic

4

What is covalent bonding?

Sharing of or more pairs of electrons between two atoms

5

What is polar covalent bonding

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

6

What is ionic bonding?

Electrostatic force of attraction between oppositely charged ions

7

What are weak Van Der Waals forces?

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

8

What are permanent dipole-dipole attractions

Permanently polarised molecules attract polarised neighbour, where opposite ends attract

9

What is hydrogen bonding?

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

10

What is electronegativity?

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

11

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

i) pure covalent
ii) polar covalent

CHART
0 - 0.7 - 1.7


cov - pol cov - ionic

12

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

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

13

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?

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

14

What is water of crystallisation?

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

15

Give two uses of noble gases

Helium - in blimps
Argon - in light bulbs

16

What is the octet rule?

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

17

What are the exceptions to the octet rule?

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

18

What is valency?

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

19

What group of elements have variable Valencies and give an example

Transition elements

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

20

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

Positively charged - Cation

21

How is a cation smaller than the corresponding atom?

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

22

Characteristics of Ionic Substances

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

23

Give examples of ionic materials in everyday life

Salt tablets - to replace salt lost in sweating
Brine - curing bacon

24

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

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

25

Characteristics of Covalent Bonding

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

26

Give examples of polar materials in every day life

Water - washing clothes
Glucose - lucozade

27

Give examples of non - polar materials in every day life

Petrol
Cooking oil

28

Account for the general trend of electronegativity across a period

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

29

Account for the general trend of electronegativity down a group

-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

Distinguish between a sigma and a pi covalent bond

Sigma - end on overlap of orbitals
Pi - sideway overlap of p orbitals

31

What does the electron repulsion theory state?

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

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

Valency = 2
2 bonds
Linear, V-shaped

33

Account for the difference in shape of NH3 and BF3

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

34

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

Sigma = 1
Pi = 2

35

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

Van Der Waals, it is non polar

36

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

No lone pairs - Linear
Lone pairs - V-shaped

37

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

No lone pairs - Trigonal Planar
Lone pairs - Pyramidal

38

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

Lone pairs - Tetrahedral

39

What bond angle does linear have?

180

40

What bond angle does v shape planar have?

104.4

41

What bond angle does trigonal planar have?

120

42

What bond angle does pyramidal have?

107.3

43

What bond angle does tetrahedral have?

109.5

44

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

Intramolecular - polar covalent bonding
Intermolecular - hydrogen bonds

45

What is the molecular formula of benzene

C6H6

46

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

Boron - three bond pairs
Nitrogen - three bond pairs and one lone pair

47

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

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

What is bond energy?

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

49

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

Stronger intermolecular forces (dipole-dipole)

50

Which are the non polar bond shapes?

Linear, trigonal planar, and tetrahedral.

51

Which are the polar bond shapes?

V-shaped and Pyramidal

52

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

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

53

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

Melting point
Boiling point
Density
Solubility in water

54

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

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

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)

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

NH3, PH3, AsH3
Which if any of the three hydrides would you expect to have intermolecular hydrogen bonding and justify

NH3
Hydorgen is bonded to Nitrogen - small and very electronegative

57

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

i) Hydrogen bond - strongest of intermolecular forces
ii) Smaller mr

58

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

Find electronegativity values and see if nonpolar or polar

59

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

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

60

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

Symmetry of molecule - Centres of positive and negative charges coincide

61

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

Molten - ions free to move
Solid - not free, fixed

62

Show that the ammonia molecule has polar covalent bonding

The electronegativity difference between N and H show unequal sharing

63

Describe the processes involved when ammonia dissolves in water

-Breaking of hydrogen bonds in water
-Forming of hydrogen bonds between ammonia and water

64

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

Weaker bonding in ammonia (small e.n difference)

65

Draw a diagram illustrating hydrogen bonding in ammonia

H H
H N - H N
H H

66

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

very weak intermolecular forces

67

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

much stronger hydrogen bonds between water molecules

68

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

polarity of water causes attraction to charged rod
non-polarity of cyclohexane means it is not affected by charged rod

69

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

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

70

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

Only slightly - weakly polar

71

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

one sigma and two pi

72

Why will water always be deflected by any charged rod?

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