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Chemistry Y12 > P- Bonding =) > Flashcards

P- Bonding =) Flashcards

1
Q

Explain why iodine has a higher melting point than fluorine. (2)

A
  • ↑ e-
  • ↑ VdW
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2
Q

Explain why bromohexane has a higher boiling point than bromobutane. (1)

A
  • ↑/ stronger vdW between molecules
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3
Q

Although phosphine (PH3) molecules contain hydrogen atoms, there is no hydrogen bonding between phosphine molecules.

Suggest an explanation for this. (1)

A

Difference in electronegativity between H & P is too small.

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4
Q

Explain, in terms of electronegativity, why the boiling point of H2S2 is lower than H2O2. (2）

A
  • electronegativity difference between H & S ↓
  • X H bonding BETWEEN H2S2 MOLECULES
    – only vdW between molecules
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5
Q

Explain what is meant by the term macromolecular,
and why macromolecular crystals have high melting points. (3)

A

Macromolecular- giant molecule w/ covalent bonding
- covalent bonds must be broken to melt
- which are strong
- many covalent bonds ∴ ↑ energy to break

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6
Q

Explain why:
1. a Na atom is larger than a Cl atom
2. a Na ion is smaller than a Cl ion
(6)

A
    • Cl: ↑ nuclear charge
    • both atoms have 3 shells
    • Cl: ↑ attraction by nucleus ∴ smaller atom
    • Na loses 1 e- shell when ion formed
    • inner e- ↑ strongly attracted ∴ ion smaller than atom
    • Cl gains 1 e- shell when ion formed
    • ↑ REPULSION between shells ∴ size of chloride ion > atom
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7
Q

Why do XeF4 & PF3 have their shapes,
and how does it affect their melting points?

A
  • XeF4: 4 bond pairs + 2 lone pairs –> square planar
  • PF3: 3 bond pairs + 1 lone pair –> trigonal pyramid
  • e- as far apart as poss ∵ repulsion–> l-l > l-b repulsion
  • XeF4 vdW vs PF3 dipole-dipole
  • stronger IM forces in XeF4
  • ∵ ↑ Mr
    // square planar= flat–> √ stack ∴ pack ↑ closely tgt
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8
Q

Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules. (2)

A
  • bond polarity ∵ diff. in electronegativity
  • attraction between ∂+ on one molecule & ∂− on another
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9
Q

State the element in Period 3 that has the highest melting point.
Explain your answer. (3)

A

Silicon
- covalent bonds
- which are strong
- there are lots of them to be BROKEN
- a lot of energy needed to break the bonds

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10
Q

Explain why iodine has a higher melting point than fluorine. (2)

A
  • ↑ Mr/ ↑ molecule
  • ↑/ stronger VdW forces between molecules
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11
Q

Why is ice less dense than water? (1)

A
  • H2O molecules further apart
  • ↑ space in structure
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12
Q

There are two lone pairs of electrons on the oxygen atom in a molecule of oxygen difluoride (OF2).
Explain how the lone pairs of electrons on the oxygen atom influence the bond angle in oxygen difluoride. (2)

A
  • lone pairs repel ↑ than bond pairs
  • bond angle ↓ than regular tetrahedral angle
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13
Q

Silicon tetrafluoride (SiF4) is a tetrahedral molecule.

Deduce the type of intermolecular forces in SiF4.

Explain how this type of intermolecular force arises and why no other type of intermolecular force exists in a sample of SiF4. (3)

A
  • VdW
  • uneven distribution of e- in one molecule INDUCES dipole in its neighbouring molecule
  • symmetrical molecule–> dipoles cancel out–> x permanent d-d interactions
  • x H bonded to F –> x H bonding
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14
Q

State and explain the bond angle in NCl4+. (2)

A
  • 109.5
  • e- pairs repel–> as far apart as possible
  • all bond pairs- repel equally
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15
Q

In which substance do covalent bonds break when it melts?
A. hexane
B. ice
C. iodine
D. silicon dioxide

A

D

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16
Q

Explain why methanol is easy to liquefy. (1)

A
  • H bonding- strong
  • hold methanol molecules tgt in a liquid
17
Q

Which statement about inorganic ionic compounds is always correct?
A. They dissolve in water to give neutral solutions.
B. They release energy when they melt.
C. They contain metal cations.
D. They form giant structures.

A

D- giant structures

18
Q

In terms of electron pairs, explain why the bond angles in the NH4+ ion are all 109.5°. (4)

A
  • 4 bond pairs
  • repel equally
  • as far apart as poss
  • TETRAHEDRAL SHAPE
19
Q

By reference to all the atoms involved, explain, in terms of electrons, how Na2S is formed from its atoms. (2)

A
  • e- TRANSFERRED from Na to S
  • 2 Na atoms, 1 e- from each
20
Q

Explain why the melting point of aluminium is higher than the melting point of sodium. (3)

A
  • ↑ nuclear charge
  • ↑ delocalised e-
  • stronger metallic bonds / electrostatic attraction between nuclei + delocalised e-
21
Q

Chlorine has a low boiling point because the forces between the molecules are weak.
Explain how these forces arise between molecules of chlorine. (3)

A
  • random movement of e- in 1 molecule –> creates temp dipole (imbalance of e- density)
  • induces dipole in a neighbouring molecule
  • temp dipoles attract
22
Q

Chloroethene has a melting point of −154ºC.
All types of PVC melt at temperatures over 100 ºC.
Explain why PVC melts at a higher temperature than chloroethene. (2)

A
  • ↑Mr/ bigger molecule
  • stronger vdW forces between molecules
23
Q

Which is not responsible for conducting electricity?
A. Sodium ions in molten sodium chloride
B. Electrons between layers of carbon atoms in graphitw
C. Bonding electrons in a metal
Lone pair electrons in liquid water molecules

A

D!

24
Q

Sodium oxide and magnesium oxide are both ionic structures.
Explain why magnesium oxide has a higher melting point than sodium oxide. (3)

A
  • Mg2+ - smaller ions
  • ↑ highly charged
  • stronger attraction to O2- ions
25
Q

Exlpain, in terms of their type of structure and bonding, why P4O10 can be vaporised by gentle heat but SiO2 cannot. (4)

A
  1. P4O10- molecular structure (/ simple covalent)
  2. weak IMF betw. molecules
  3. SiO2- macromolecule (/ giant covalent)
  4. strong covalent bonds betw. atoms must be broken
26
Q

Predict whether the melting point of lithium oxide is higher than, the same as, or lower than the melting point of sodium oxide and explain your prediction. (3)

A
  • higher
  • Li+ smaller than Na+
  • stronger attraction to O2-
27
Q

A reaction mixture contains propanal, propan-1-ol and propanoic acid.
boiling points: propanoic acid > propan-1-ol > propanal
Explain, with reference to intermolecular forces, why distillation allows propanal to be separated from the other organic compounds in the mixture. (3)

A
  1. propanal- dipole-dipole
  2. propan-1-ol & propanoic acid- H bonds betw. molecules
  3. forces betw. molecules in propanal- weaker than those in propan-1-ol & propanoic acid –> evaporate first
28
Q

State why iodine does not conduct electricity. (1)

A

x delocalised e-/ (mobile) ions

29
Q

Define the term electronegativity. (1)

A

the tendency of an atom to attract a pair of e- (/ e- density) in a covalent bond

30
Q

List the following period 3 elements in the order of increasing melting points:
phosphorus, sulfur, chlorine, argon
(1)

A

sulfur > phosphorus > chlorine > argon
* P4- weak vdW
* S8- bigger molecule, stronger vdW

31
Q

Describe the structure and bonding in magnesium. (2)

A
  • giant lattice of Mg2+ ions
  • electrostatic attractions betw. Mg2+ ions & delocalised e-

Chemistry Y12 (33 decks)

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