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physical chemistry > 3.1.3.4 Bonding and physical properties- boiling/melting point > Flashcards

3.1.3.4 Bonding and physical properties- boiling/melting point Flashcards

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1
Q

why the boiling point of methanol is much higher than that of oxygen

A

van der Waals’ forces between oxygen molecules
Hydrogen bonding between methanol molecules
H-B stronger than van der Waals’ O
R stronger IMF in methanol

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2
Q

the trend in melting point of the Group II elements Ca–Ba.

A

Trend: Decreases
Increase in size of ion/atom / more shells / decrease in charge density / decrease in charge size ratio
Weaker attraction for delocalised/free/sea of electrons / weaker metallic bonding

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3
Q

the trend in the melting points of the Period 3 metals Na, Mg and Al

A

trend: increases
more protons / higher charge on cation / more delocalised e– / smaller atomic/ionic radius
stronger attraction between (cat)ions and delocalised/free/mobile e–
OR stronger metallic bonding

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4
Q

why magnesium has a higher melting point than sodium

A 
more protons (
(or Mg2+ more charge than Na+ ) attracts delocalised (or bonding) electrons more strongly
more delocalised electrons
Attacks positive ions more
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5
Q

Why diamond and graphite both have high melting points

A

macromolecular
(or giant molecule etc) covalent
strong covalent bonds

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6
Q

Change that occurs to the motion of the ions in sodium chloride when it is heated from room temperature to a temperature below its melting point

A

vibrate faster

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7
Q

why the boiling point of AsH3 is lower than that of NH3

A

(Only) weak Van der Waals forces between molecules /AsH3 has weaker IMF /ammonia has hydrogen bonding/ more energy needed to break IMF’s in ammonia/ Van der Waals weaker than H bonds;

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8
Q

Predict the type of bonding in a crystal of sodium azide. Suggest why its melting point is high.

A

Ionic
Oppositely charged ions / Na+ and N3 – ions
Strong attraction between (oppositely charged) ions / lots of energy needed to overcome (strong) attractions (between ions)

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9
Q

why nickel has a high melting point

A 
Contains positive (metal) ions or protons or nuclei and delocalised / mobile / free / sea of electrons
Strong attraction between them or strong metallic bonds
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10
Q

State the type of bonding in lithium fluoride. Explain why a lot of energy is needed to melt a sample of solid lithium fluoride.

A

Ionic
Strong or many or lots of (electrostatic) attractions (between ions)
Between + and − ions / between Li+ and F− ions / oppositely charged ions

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11
Q

why graphene has a high melting point

A

Covalent bonds

Many /strong / hard to break / need a lot of energy to break

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12
Q

why titanium has a high melting point

A

Nucleus / protons / positive ions and delocalised electrons (are attracted)
Strong attraction

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13
Q

the type of crystal structure in magnesium oxide and suggest why its melting point is high

A

(giant) Ionic
Between + and – ions / oppositely charged ions or Mg2+ and O2–
Strong attraction

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14
Q

why the melting point of sodium chloride is high

A

Strong (electrostatic) attraction

Between oppositely charged ions / particles

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15
Q

why the melting point of sodium iodide is lower than the melting point of sodium bromide

A

Iodide / I– bigger (ion) (so less attraction to the Na+ ion)

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16
Q

why KBrF4 has a high melting point

A 
Ionic or (forces of) attraction between ions / bonds between ions
Strong (electrostatic) attraction / strong bonds / lots of energy needed to break bonds
Between K+ and BrF4 – ions/oppositely charged ions / + and – ions
17
Q

why the melting point of carbon is high

A

Macromolecular / giant molecular / giant atomic
Covalent bonds in the structure
Strong (covalent) bonds must be broken or overcome / (covalent) bonds need a lot of energy to break

18
Q

the type of bonding in sodium sulfide (Na2S) and explain why its melting point is high

A

Ionic
oppositely charged ions/+ and – ions or particles
ions attract strongly OR strong/many (ionic) bonds must be broken

19
Q

why sodium has a lower melting point than magnesium

A

Na fewer protons/smaller nuclear charge/ fewer delocalised electrons
Na is a bigger ion/ atom
Smaller attraction between nucleus and delocalised electrons

20
Q

Melting point of ice compared to sodium chloride

A

Attraction between ions in sodium chloride is very strong
Covalent bonds in ice are very strong
Hydrogen bonds between water molecules in ice are much weaker
Consequently, less energy is required to break the hydrogen bonds in ice to form separate water molecules than to break the ionic bonds in sodium chloride and make separate ions

21
Q

The melting point of sodium chloride is much higher than that of sodium metal. What can be deduced from this information

A

the ionic bonding in NaCl is stronger/requires more energy to break than the metallic bonding in Na

22
Q

why magnesium has a higher melting point than sodium

A 
more protons
attracts delocalised (or bonding) electrons more strongly
23
Q

Why diamond and graphite both have high melting points

A

Macromolecular
Covalent
strong covalent bonds
bonds require much energy to break

24
Q

why the heat energy required to melt sodium chloride is large

A

Ionic
Strong forces between ions
lots of energy required to break bonds

25
Q

Why the heat energy needed to vaporise one mole of sodium chloride (171 kJ mol–1) is much greater than the heat energy required to melt one mole of sodium chloride

A

All bonds must be broken

26
Q

why graphite has a very high melting point

A

Macromolecular
Strong covalent bonds
lots of energy required to break bonds

27
Q

Although propane has a boiling point of –42 °C, it is usually supplied as a liquid for use in camping stoves. Suggest why it is supplied as a liquid.

A

Occupies a (much) smaller volume;

28
Q

BrF4 – ions are also formed when potassium fluoride dissolves in liquid BrF3 to form KBrF4 Explain, in terms of bonding, why KBrF4 has a high melting point.

A 
Ionic or (forces of) attraction between ions / bonds between ions
Strong (electrostatic) attraction / strong bonds / lots of energy needed to break bonds
Between K+ and BrF4 – ions/oppositely charged ions / + and – ions
29
Q

Predict the type of bonding in a crystal of sodium azide. Suggest why its melting point is high.

A

Ionic
Oppositely charged ions / Na+ and N3 – ions
Strong attraction between (oppositely charged) ions / lots of energy needed to
overcome (strong) attractions (between ions)

30
Q

the element in Period 3 that has the highest melting point

A

Silicon / Si
covalent (bonds)
Strong or many of the (covalent) bonds need to be broken / needs a lot of energy to break the (covalent) bonds

31
Q

why the melting point of silver fluoride is high

A

Strong (electrostatic) forces/bonds

Between + and – ions

32
Q

why heat energy is required to melt an iodine crystal

A

Bonds (or forces) between molecules must be broken or loosened

physical chemistry (18 decks)

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