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Chemistry (Tara) > Atomic theory 10 > Flashcards

Atomic theory 10 Flashcards

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1
Q

What is intermolecular bonding?

A

An attractions between atoms of different molecules

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2
Q

Define hydrogen bonding

A

A hydrogen bond is a force of attraction that occurs between molecules when hydrogen is bonded to a smaller more electronegative element such as O, F or N.

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3
Q

When does hydrogen bonding occur?

A

When hydrogen is bonded, in a molecule to a smaller more electronegative element like F, O or N

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4
Q

When does the most effective H-bonds occur?

A

When H is bonded to F, O or N.

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5
Q

Can hydrogen bonding only occur within or between a molecule

A

ONLY BETWEEN!!

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6
Q

Is a lot of energy needed to break hydrogen bonds?

A

Yes more energy is needed to break them

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7
Q

Why is more energy needed to break hydrogen bonds?

A

Due to their presence

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8
Q

Why does water have a high boiling point?

A

Due to the presence of hydrogen bonds, more energy is needed to break them down

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9
Q

Why is water a liquid at r.t and H2S a gas?

A

Because the intermolecular forces of attraction between H₂S molecules are considerably weaker than the hydrogen bonding between water molecules, hence the molecules in hydrogen sulfide are freer to move apart making H₂S a gas.

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10
Q

What are polar molecules attracted to?

A

Other polar molecules

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11
Q

Polar molecules are attracted to other polar molecules. What kind of attraction is this and what is it known as?

A
  • An attraction between atoms of different molecules

- known as intermolecular bonding / dipole-dipole attractions.

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12
Q

Are attractions between ions strong or weak?

A

Extremely strong

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13
Q

Attractions between ions are extremely strong. What does this give rise to?

A

Gives rise to ionic compounds being crystalline solids.

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14
Q

Do the attractions between ions have high or low boiling points and melting points?

A

High

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15
Q

Are dipole-dipole attractions between covalent molecules stronger or weaker in comparison to the attractions between ions?

A

Weaker

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16
Q

Hydrogen bonding is a special type of ……..

A

Intermolecular force of attraction (dipole-dipole interaction)

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17
Q

What are hydrogen bonds stronger than?

A

Other types of dipole-dipole interactions.

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18
Q

Give an example of hydrogen bonding

A

Hydrogen bonding between H₂O molecules

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19
Q

Are hydrogen bonds strong or weak?

A

Relatively weak, but exert a large influence on the physical and chemical properties on the molecules that form them.

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20
Q

Does water have a relatively high or low boiling point compared to molecules of similar molecular mass

A

High

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21
Q

What does hydrogen bonding account for in water?

A

The high solubility’s of polar compounds in water.

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22
Q

Give two examples of common molecules that have hydrogen bonding between the molecules.

A

HF

NH₃

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23
Q

What are Van der Waal’s forces?

A

Weak intermolecular forces of attraction that exist between all states of matter.

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24
Q

What are Van der Waal’s forces caused by?

A

Caused by the internal shifts in the electrons in the molecule.

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25
Q

Why is there a temporary dipole set up in the molecule of Van der Waal’s forces of attraction?

A

As at any given time the electrons being shared may be closer to one end of the molecule than the other.

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26
Q

Does it require a lot of energy to break Van der Waal’s forces?

A

No

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27
Q

What attract each other using Van der Waal’s forces of attraction?

A

Non-polar molecules

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28
Q

What are the only intermolecular forces of attraction between gaseous molecules?

A

Van der Waal’s forces.

29
Q

What are dipole-dipole interactions?

A

Weak intermolecular forces of attraction between polar molecules.

30
Q

What are dipole-dipole interactions described as being?

A

Permanent dipoles

31
Q

Why are dipole-dipole interactions described as being permanent dipoles?

A

As the molecules are constantly polar.

32
Q

Is the energy needed to break dipole-dipole attractions constant or does it vary?

A

Varies

33
Q

How much energy is need to break dipole-dipole interactions, in comparison to Van der Waal’s and hydrogen bonding?

A

More energy than that needed to break Van der Waals and less than needed to break Hydrogne bonding.

34
Q

What are the boiling point of a substance and its state of matter determined by?

A

(a) the strength of the intermolecular forces of attractions

(b) the size of the molecule

35
Q

The stronger the intermolecular forces and the larger/heavier the molecule …………………………

A

the more energy will be required to break the molecules up from each other.

36
Q

How polar are ionic compounds?

A

Extremely polar

37
Q

Which compounds have the strongest forces of attractions?

A

Ionic compounds

38
Q

Which compounds have high boiling points and are usually crystalline solids?

A

Ionic compounds

39
Q

What compounds have relatively lower boiling points and may be liquids?

A

Polar covalent compounds that have hydrogen bonding between the molecules.

40
Q

What compounds have high boiling points, may be gases and are slightly weaker than polar compounds that have hydrogen bonding between the molecules?

A

Polar covalent compounds that have dipole-dipole interactions.

41
Q

What compounds have extremely low boiling points and generally tend to be gases (but exceptions occur)

A

Compounds with the very weak Van der Waal’s forces.

42
Q

Checklist for questions on states of matter or boiling points.

A

1, Get electronegativity difference to determine the type of intramolecular bonding.

  1. ↳ This will then determine the strength of the inter bonding i.e. intra = ionic, inter = extremely strong etc.
  2. ↳ reason for the state of matter or the high or low boiling point and the size of the molecule.
43
Q

Use electronegativity values to predict the type of bond expected between hydrogen and sulfur. (L.C)

A

Weakly polar / almost non-polar

44
Q

Write the chemical equation for hydrogen sulphide. (L.C)

A

H₂S

45
Q

Would you expect the hydrogen sulphide molecule to be linear or non-linear in shape? Justify your answer.(L.C)

A
  • Non-linear

- There are lone(non-bonding) pairs

46
Q

Hydrogen sulphide has a boiling point of 212.3 K and water has a boiling point of 373 K. Account for the difference in the boiling points of these substances. (L.C)

A
  • Water has hydrogen bonds
  • Weak dipole-dipole forces in H₂S /
  • Weaker intermolecular forces in H₂S
47
Q

Would you expect hydrogen sulphide to be soluble in water? Explain your answer. (L.C)

A
  • No / only slightly soluble

- Does not form hydrogen with water

48
Q

Explain the term intermolecular forces (L.C)

A

Attractive (repulsive) forces between molecules.

49
Q

Use your knowledge of intermolecular forces to explain why methane has a very low boiling point (164°C) (L.C)

A
  • Very weak intermolecular forces

- Weak Van der Waal’s forces of attraction

50
Q

The relative molecular mass of methane is only slightly lower than that of water but the boiling point of water is much higher (100°C). Suggest a reason for this. (L.C)

A
  • Much stronger hydrogen bonds between water molecules
51
Q

Why do ionic substances conduct electricity when molten or dissolved in water but not in the solid state? (L.C)

A

Molten/dissolved : ions free to move

Solid : ions not free to move / ions locked in position

52
Q

Show that the ammonia molecule (NH₃) has polar covalent bonding. Describe the processes involved when ammonia dissolves in water. (L.C)

A
  • There is an electronegativity difference between N and H
  • Showing unequal sharing
  • N with greater attraction
53
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

54
Q

Account for the difference in bond angle between the two molecules, 107.3 degrees in ammonia and 109.5 degrees in silane. (L.C)

A
  • Lone pair of electrons has greater repelling power than a bond pair of electrons.
  • Bonds in NH₃ pushed closer together than in SiH₄
  • Ammonia has three bond pairs where silane has four bond pairs
55
Q

Use electronegativity values to determine which bond, the N-H bond in ammonia or the Si-H bond in silane, is the more polar. (L.C)

A

N - H = 0.84
Si - H = 0.3
⇒
N - H is more polar

56
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

57
Q

Use electronegativity values to determine which bond, the N-H bond in ammonia or the Si-H bond in silane, is the more polar. (L.C)

A

N - H = 0.84
Si - H = 0.3
⇒ N - H is more polar

58
Q

Which of the two substances ammonia (NH₃) or silane (SiH₄) has hydrogen bonding between its molecules? Justify your answer. (L.C)

A
  • Ammonia

- In ammonia hydrogen bonded to a small highly electronegative element

59
Q

Give the reason why a molecule with polar bonds can be non-polar. (L.C)

A
  • Centres of positive and negative charge coincides

- Dipole moments cancel

60
Q

Why is there an increase in electronegativity value moving from gallium to germanium in the periodic table? (L.C)

A
  • Nuclear charge increasing

- Atomic radius increasing

61
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond..

62
Q

Write the molecular formula for the simplest compound formed between germanium (IV) and hydrogen. (L.C)

A

GeH₄

63
Q

Would you expect the compound GeH₄ to be water soluble? Explain your answer. (L.C)

A
  • No

- GeH₄ is a non-polar solute

64
Q

Suggest a reason why ammonia has the highest boiling point of ammonia, phosphine and arsine. (L.C)

A

Hydrogen bonding in ammonia (azane) is stronger than the other intermolecular forces in phosphane or arsane.

65
Q

Suggest a reason why phosphine’s boiling point is lower than that of arsine. (L.C)

A
  • Phosphine molecules are smaller

- Phosphine has a smaller degree of intermolecular forces

66
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

67
Q

Use electronegativity values to predict the type of bonding in chlorine monofluoride. (L.C)

A

Polar covalent

68
Q

Define electronegativity (L.C)

A

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.,

Chemistry (Tara) (50 decks)

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