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A - Level Chemistry > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

What is the bonding like in an alkane?

A
  • 2 p-orbitals, 1 from each bonding atom
  • overlap and contain 1 electron each
  • sigma bond has 2 electrons that are shared between bonding atoms
  • each carbon in an alkane has 4 sigma bonds
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2
Q

What is a sigma bond?

A

The head on overlap of 2 p-orbitals, 1 from each bonding atom, directly between the bonding atoms nuclei.

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3
Q

How many bonds can a Carbon form in an alkane?

A

4 covalent bonds

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4
Q

Are alkanes saturated or unsaturated?

A

They’re saturated hydrocarbons (they contain single bonds only)

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5
Q

What is the general formula of an alkane?

A

CnH2n+2

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6
Q

What’s is the shape of an alkane?

A
  • tetrahedral shape
  • bond angle = 109.5*
  • caused by = each c atom surrounded by 4 e pairs in 4 sigma bonds, repulsion between these e pairs cause this shape around each C atom
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7
Q

Why does the boiling points of alkanes increase as the chain length increases?

A
  • because of weak IMF, LFs
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8
Q

What is the effect of chain length on boiling point?

A
  • chain length increases
  • increases surface area
  • Greater (stronger) London forces
  • more energy required to overcome the forces
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9
Q

What’s is the effect of branching on boiling point?

A

(Example may include isomers of alkanes- branched isomers has lower boiling point than straight chain isomers)

  • more branching
  • fewer surface points of contact (decreased surface area)
  • weaker (fewer) London forces

Also another reason is to do with the shape.
- branches get in the way and prevent branched molecules getting as close together as straight chain molecules, decreasing IMFs further

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10
Q

What is an alkane?

A

A saturated hydrocarbons containing C-H bonds only.

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11
Q

What is the general formula of an alkane?

A

CnH2n+2

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12
Q

Are alkane bonds polar? Why/why not?

A

Non-polar because carbon and hydrogen have similar electronegativities.

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13
Q

What is the shape and angle of an alkane?

A

Tetrahedral

109.5*

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14
Q

Describe the sigma bond in alkane?

A

The sigma bond is a covalent bond which has a direct overlap of the electron clouds of the bonding atoms.

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15
Q

What type of intermolecular forces do alkanes have? Why?

A

London forces -> induced dipole-dipole interaction, because the bonds are non-polar

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16
Q

What happens to the boiling point as alkane chain length increases? Why?

A

The boiling point increases because there is more surface area and so more number of induced dipole-dipole interaction. Therefore more energy required to overcome the attraction.

17
Q

Does a branched molecule have a lower or higher boiling point compared to equivalent straight chain? Why?

A

The branched molecule has a lower boiling point because they have fewer surface area and hence less induced dipole-dipole interactions.

18
Q

Are alkanes soluble in water? Why?

A

Insoluble because hydrocarbon bonds in water are stronger than alkanes’ London forces of attraction.

19
Q

How reactive are alkanes?

A

Very unreactive

20
Q

What reactions will alkanes undergo?

A

Combustion and reaction with halogens

21
Q

What type of reaction is combustion?

A

Oxidation reaction

22
Q

What is complete combustion?

A

Combustion that occurs with plentiful supply of air

23
Q

What are the products of complete combustion when alkanes are used?

A

Carbon dioxide and water

24
Q

What is the colour of the Bunsen burner flame during complete combustion?

A

Blue flame

25
Q

What is incomplete combustion and what products are formed in the case of alkanes?

A

Combustion in a limited supply of oxygen

Products = water, carbon dioxide and carbon monoxide

26
Q

Write an equation for the complete combustion of propane?

A

C3H8 + 5O2 —> 3CO2 + 4H2O

27
Q

What type of hydrocarbon are most likely to undergo incomplete combustion?

A

Longer chains

28
Q

What is the environmental impact of carbon monoxide?

A

It is toxic/poisonous

29
Q

What is the environmental impact of soot (carbon)?

A

Asthma, cancer, global dimming

30
Q

How are halogenoalkanes formed from alkanes?

A

Free radical substitution

31
Q

In the presence of what does alkane react with halogens?

A

UV light
(Sunlight)

32
Q

What are the 3 stages of free radical substitution?

A

Initiation - breaking halogen bond to form free radicals

Propagation - chain part of the reaction where products are formed but free radicals remains.

Termination - free radicals removed, stable products formed

33
Q

Write equations for the reaction of CH4 with Cl2 to form CH3Cl

A

Initiation: Cl2 —> 2Cl* (in presence of UV light)

Propagation: Cl* + CH4 —>HCl + *CH3
CH3 + Cl2 —> CH3Cl + Cl

Termination:
CH3 + Cl —> CH3Cl
2Cl* —> Cl2
*CH3 + *CH3 —> CH3CH3

A - Level Chemistry (5 decks)

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