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Edexcel Chemistry Unit 1 IAL (WCH01) Core principles of chemistry - 23rd May 2014

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Reply 80

ybadri

what dd u write for why the bond energy for cl-cl bond greater than for f-f bond?

Reply 81

Vivekmaj

Original post by saifulahmed

for orbital i think the third one will be 8 or 16.
for the rest i hope they are correct cause i got the same answers.

No! the one of n=3 has two ways to get, you can use the formula 2n^2 or add the subshells (S+P+D) EITHER WAY YOU GET 18 as those are the max no of electrons if however they stated that it follows the octet rule then your answer of 8 would be correct

Reply 82

Vivekmaj

Original post by ybadri

what dd u write for why the bond energy for cl-cl bond greater than for f-f bond?

I only answered the question where it asked why F-F bond has a higher bond enthalpy, the one where the question was vice versa made me blank and i had no clue

Reply 83

Fattyma97

So is it 8 or 18?

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Reply 84

Fattyma97

Original post by Vivekmaj

I only answered the question where it asked why F-F bond has a higher bond enthalpy, the one where the question was vice versa made me blank and i had no clue

Sameeee they can't make us contradict ourselves

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Reply 85

Vivekmaj

Original post by Fattyma97

So is it 8 or 18?

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Reply 86

koko1234

Original post by Fattyma97

Sameeee they can't make us contradict ourselves

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Me too!!

Reply 87

Ripper Phoenix

lmao i just googled it and F-F is weaker than Cl-Cl... they say because of some repulsions..come on guys google it!!!

Reply 88

Ripper Phoenix

even though i wrote something diff in the exam paper! :redface:

Reply 89

Ripper Phoenix

Original post by noosh_s

could someone make an unofficial mark scheme please???

it would be difficult! there were too many questions lol .. going to see my tuition teacher soon so will clarify all doubtts!

Reply 90

isam nazer

what is the answer of the question about the E and Z ismoers ?

Reply 91

hhalai96

for the mean bond enthalpy .. was the answer suppose to be +416 or - ??
lattice enthalpy = -1046
for he h20 thing = -77

Reply 92

hhalai96

Original post by Vivekmaj

I only answered the question where it asked why F-F bond has a higher bond enthalpy, the one where the question was vice versa made me blank and i had no clue

i wrote F-F has a shorter bond hence more force of attraction compare to CL-Cl bond which is longer ...
for the next question i was blank toooo...
and in that same question the last one where it says why F-F bond don't require UV ... is it fine if you write fluorine is more reactive than chlorine

Reply 93

Fattyma97

I wrote that too!!! Btw, I really hope the grade boundaries aren't too high for an A what do u think they will be

Reply 94

Ripper Phoenix

Original post by Fattyma97

I wrote that too!!! Btw, I really hope the grade boundaries aren't too high for an A what do u think they will be

well tbh jan 14 was easy and the boundary was 58 .. now for this paper.. it was tricky and goood.. so i am expecting a 60 mark for the A.. what do u think?

Reply 95

Ripper Phoenix

Bond energy (in kJ/mol)

F-F:158
Cl-Cl: 244
Br-Br-:193
I-I: 151

Hence, in order of decreasing bond strength:
Cl-Cl => Br-Br => (F-F) => I-I
Fluorine is an anomaly.

Bond strength decreases from chlorine to iodine as down the group, the atomic size becomes larger and thus the valence electron orbitals become more diffused, causing the overlap of orbitals to become less effective. Therefore the halogen-halogen bond becomes weaker from chlorine to iodine.

Fluorine is an exception due to its extremely small size. The F-F bond length is so short that the lone pairs of electrons on the fluorine atoms repel each other and weakens the F-F bond.

I hope that answers your question.

Reply 96

Fattyma97

Original post by Paras Agarwal

well tbh jan 14 was easy and the boundary was 58 .. now for this paper.. it was tricky and goood.. so i am expecting a 60 mark for the A.. what do u think?

Some people are saying it will be 62-65, don't u think that's a little too high? I think 60 is reasonable not higher. :no:

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Reply 97

avishyaa

what do you guys think the grade boundaries will be for an A?
Because if many people find it tricky, the grade boundaries could always go to a 56-58 as well. It just depends on the overall performance