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Another Chem A levels > 2.5 Hydrocarbons > Flashcards

2.5 Hydrocarbons Flashcards

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1
Q

Well if u seem concerned, go see the first few pages if ya want

A

Okay

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2
Q

What are free radicals?

A

Atoms/groups of atoms which have a single unpaired electron

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3
Q

How are free radicals formed?
What name for it?

A

Bond splits evenly - each atom having one of the 2 electrons
Homolytic fission

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4
Q

What are the 3 stages of Homolytic fission?

A

Stage 1 - Initiation
Stage 2 - Propagation
Stage 3 - Termination

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5
Q

Explain intitiation stage?

A

UV radiation causing a [chlorine-chlorine] bond to split homolytically

(symbol for radical is that full stop on the top right of it) aka

Cl]-[Cl (U.V)-> Cl˙ + Cl˙ OR Cl2 (UV)-> 2CL˙ (Chlorine radicals)

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6
Q

Explain propagation stage?

A

Radicals = reactive ∴ take part in a series of propagation reactions

CH4 + Cl˙ -> ˙CH3 + HCl
CH3 + Cl2 -> CH3Cl + ˙Cl

There’s a diagram for dat one too + chain reaction type sh forming radical as a product

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7
Q

Explain termination stage?

A

Cl˙ + Cl˙ -> Cl2
Cl˙ + ˙CH3 -> CH2Cl
˙CH3 + ˙CH3 -> CH3CH3

Propagation will continue until two radicals meet = termination

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8
Q

How are alkenes more reactive than alkanes?

And ig how alkenes forms bonds or summin?

A
  • Alkenes more electron density
  • Due to more as there are 2 electron pairs = 4 electrons
  • Centred between carbons either side of double bond
  • Can use one electron pair in double bond to react and form new bonds to each carbon atom
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9
Q

What happens to alkanes when their one electron pair is used?

A
  • Sigma bond broken
  • Molecule destroyed
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10
Q

U also gotta look at page 6 for them reactivity of alkene n alkane n stuff

A

Okay

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11
Q

Explain how alkenes give rise to pi bonds?
And ig what that means too?

A

During carbon bond, as second bond (second pair of electrons) created, overlap of the p-orbitals of the 2 carbon atoms happen, forming pi bonds (area of high electron density) above and below plane of molecule.

This is why it’s a double bond???? idk

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12
Q

Or just go to page 7 for alkenes related bonding thing

A

Okay

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13
Q

What it mean for carbon-carbon double bonds having restricted rotation?

A
  • No free rotation due to pi-bond
  • Therefore even tho it’s the same molecules,
  • It’s a different thing due to it’s position
  • That’s why carbon-carbon single bonds would still have the same name despite different position of molecules
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14
Q

Define electrophile?

A

Atom (or group of atoms) attracted to an electron-rich centre/atom. Accepts a pair of electrons to form new covalent bond

E.g. Hbr/HCl/Cl2/Br2/H

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15
Q

Define nucleophile?

A

Chemical that can donate a pair of electrons with the subsequent formation of a covalent bond

E.g (All molecules except H have 2 dots above em, lone pair type sh)
-OH, Br-, Cl-, -CN/H2O or NH3

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16
Q

Define free radical?

A

Atom/group of atoms with an unpaired electron

E.g. ˙Cl, ˙CH3, ˙CH2CH3

17
Q

What 2 types of addition reactions ig?

A
  • Bromination
  • Hydrogenation
18
Q

4 MAIN THINGS needed to be shown in the model diagram of a reaction between an alkene and some rando ahh molecule?
(4 things)

A
  1. Curly arrows
  2. Dipoles
  3. Lone pairs
  4. Charges (full)

MAKE SURE U LOOK AT THESE PAGES FOR EASY 4 MARKS

19
Q

Look at the page for beginning of section G - Electrophilic Addition. ,’:D

A

Yikes man…

20
Q

For bromination, test for what? and how to tell if certain thing present?

A
  • Test for alkenes and presences of C=C double bonds
  • Bromine water will decolourise if C=C present
21
Q

What’s hydrogenation as well?

A
  • H added to alkenes, to saturate them
  • Forms alkanes
22
Q

Explain how u know if it’s a carbocation?
And how u know which ones more stable?

A
  • Propane? But there’s a positive ion? at the bottom of either Carbons.
    e.g. 1° - carbocation, 2° - carbocation, etc. lol
  • 1° is more stable, 3° is less.
    Additionally, 1° - carbocation has that positive ion on the bottom right, 3rd carbon :v
23
Q

But in general how to tell which carbocation stable?

A

Uhhhh, more alkyl groups attached??? (CH3 or CH2CH3)

  • Alkyl groups donate electron density to carbocation, helps stabilise
24
Q

What u use to test for alkenes? How so?

A
  • Potassium manganate(VII) solution
  • Cold state, colour depends based on acidic/alkaline conditions
25
Q

Show differences in potassium manganate(VII) solution based on acid/alkali

A

Acidified (dilute sulphuric acid) = Purple solution -> Colourless

Alkaline (sodium carbonate solution) = Purple solution -> Dark green -> Dark brown precipitate

26
Q

What’s the ick with potassium manganate(VII) solution tho?

A
  • Could give same results from the alkaline solution
    It may contain a carbon-carbon double bond. But equally it could be any one of a large number of other compounds all of which can be oxidised by manganate(VII) ions under alkaline conditions
27
Q

Aye man, u gotta be aware of carbocations n stuff, like is the addition of HBr to propene n stuff, and u can tell if it’s stable or not

A

Bruhhh

28
Q

What is addition polymerisation?

A

Addition reaction that continues until actively stopped

Biology fr

29
Q

What can be used for monomers adding together toe form long chain polymers?

(2 things)

A
  • Alkenes
  • Substituted alkenes
30
Q

The polymer doesn’t contain double bond, BUT, what is added to the name n stuff showing that it probably does?

A
  • Poly added to monomer
  • To involve ene
    e.g.
    ethene -> polyethene
31
Q

Make sure u know how to draw a monomer, how to show it’s a repeat unit?

A

Square brackets [LOL]

32
Q

Describe what happens to ethene molecules during the formation of polyethene

(3 marks)

A
  • Double bond breaks (1)
  • Electron pair forms a new covalent bond,
    on a carbon from a neighbouring (ethene) molecule (1)
  • Forming a saturated polymer chain (1)
33
Q

And ye, definitely look at the last page, and for sure, ya gotta do some exam questions

A

Okayyyy

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