Hey there! Sign in to join this conversationNew here? Join for free

Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

  • View Poll Results: Which topic(s) are you finding most difficult?
    Shapes of molecules and ions
    11.66%
    Intermediate bonding and bond polarity
    15.95%
    Intermolecular forces
    9.82%
    Redox
    17.79%
    Group 2 & 7
    40.49%
    Kinetics & Equilibria
    14.11%
    Organic Chemistry - Alcohols and Halogenoalkanes
    39.26%
    Mechanisms
    26.38%
    Green Chemistry
    28.83%

    Offline

    0
    ReputationRep:
    Thank you Zoey! I sort of understand that bit, its just when it gets a bit more complicated i.e. how to find the lone pairs in the 1st place haha.
    Offline

    0
    ReputationRep:
    (Original post by felicity95)
    Thank you Zoey! I sort of understand that bit, its just when it gets a bit more complicated i.e. how to find the lone pairs in the 1st place haha.

    Lone pairs=( group number - number of electrons used up in bonding )/2
    For example ammonia NH3 is in group 5 and so has 5 outer electrons.. out of these 3 are used in bonding. hence the lone pairs = (5-3)/2 = 1 lone pair

    so as it has one lone pair and three bond pairs ..and the lone pair-bond pair repulsion is more than bond pair-bond pair repulsion it makes an angle of 107

    the 107 angle is 2.5 less than the expected tetrahedral angle which is 109.5 because of the lone pair in it.
    http://www.meta-synthesis.com/webboo...r/balloon3.jpg
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    Looking forward to this exam, generally speaking, it's easier if you've already done/doing A2. I need 105 ums in this exam for my A overall in chem, hopefully I can pull this off

    If anyone has any questions, just post them here, the others or myself will be able to help.

    :yy:
    Offline

    0
    ReputationRep:
    (Original post by felicity95)
    Thank you Zoey! I sort of understand that bit, its just when it gets a bit more complicated i.e. how to find the lone pairs in the 1st place haha.
    ooh my bad haha
    Offline

    0
    ReputationRep:
    If anyone needs help with the VSEPR theory, I found this link incredibly helpful

    http://www.adichemistry.com/general/...pr-theory.html
    Offline

    0
    ReputationRep:
    thanks everyone. I think i understand this much better.
    Offline

    1
    ReputationRep:
    (Original post by UnknownGirly)
    Lone pairs=( group number - number of electrons used up in bonding )/2
    For example ammonia NH3 is in group 5 and so has 5 outer electrons.. out of these 3 are used in bonding. hence the lone pairs = (5-3)/2 = 1 lone pair

    so as it has one lone pair and three bond pairs ..and the lone pair-bond pair repulsion is more than bond pair-bond pair repulsion it makes an angle of 107

    the 107 angle is 2.5 less than the expected tetrahedral angle which is 109.5 because of the lone pair in it.
    http://www.meta-synthesis.com/webboo...r/balloon3.jpg
    Thanks for this. What about SO2? How do you fins how many electrons are used for bonding?

    And in the above website for SCL4, how is it that sulfur has more than 8 electrons in a shell?
    Offline

    1
    ReputationRep:
    Definition of allotropes?


    Posted from TSR Mobile
    Offline

    13
    ReputationRep:
    (Original post by NilFBosh)
    Definition of allotropes?


    Posted from TSR Mobile
    Different structural forms of the same element existing in the same physical state. ?
    Offline

    0
    ReputationRep:
    (Original post by NilFBosh)
    Thanks for this. What about SO2? How do you fins how many electrons are used for bonding?

    And in the above website for SCL4, how is it that sulfur has more than 8 electrons in a shell?
    http://diewissenschaft.wiki.hci.edu....ur_dioxide.png

    here's the dots and cross for SO2.
    cross for Sulphur, dots for oxygen
    & 2 bond pairs, 2 lone pairs, hence, the V-shaped angular shape
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by TheKingOfTSR)
    Different structural forms of the same element existing in the same physical state. ?
    That's correct!
    I'm not too sure if same physical state is strictly correct. Although I would imagine in this unit they would be referring to structures of solids

    (Original post by NilFBosh)
    Definition of allotropes?


    Posted from TSR Mobile
    Same elements but different structural arrangement like TheKingofTSR stated

    The most common example is, carbon... three of it's allotrops are; Diamond, Graphite & Buckyball (C60).
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Zoeyyy)
    http://diewissenschaft.wiki.hci.edu....ur_dioxide.png

    here's the dots and cross for SO2.
    cross for Sulphur, dots for oxygen
    & 2 bond pairs, 2 lone pairs, hence, the V-shaped angular shape
    That dot and cross diagram of SO2 makes a lot more sense to me

    I sometimes see sulfur dioxide like this:

    http://1.bp.blogspot.com/_Z60kzbFyxF...1600/apes3.png

    I even saw on chemguide SO2 shown with two double bonds :confused:
    Offline

    2
    ReputationRep:
    (Original post by NilFBosh)
    My problem is with shapes of molecules and ions. I need to know if there is a definite list of what to know or is there some way of knowing the shapes. I know the shapes of molecules which don't have lone pairs. But molecules with lone pairs is the problem for me how do you how many lone pairs are there in molecules like SO2? I don't know how to draw dot and cross diagrams for those types of molecules. Please help someone!!!
    Check the CGP book for AS level chemistry, page 64 to 65 "Shapes of Molecules" - tells you everything you need to know.
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    (Original post by posthumus)
    That dot and cross diagram of SO2 makes a lot more sense to me

    I sometimes see sulfur dioxide like this:

    http://1.bp.blogspot.com/_Z60kzbFyxF...1600/apes3.png

    I even saw on chemguide SO2 shown with two double bonds :confused:
    :yep: SO2 has double bonds in it.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by James A)
    :yep: SO2 has double bonds in it.
    But does it have two or one ?

    I see both O-S=O
    &
    O=S=O
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    (Original post by posthumus)
    But does it have two or one ?

    I see both O-S=O
    &
    O=S=O
    SO2

    O=S=O
    :yep:
    Offline

    0
    ReputationRep:
    (Original post by James A)
    Looking forward to this exam, generally speaking, it's easier if you've already done/doing A2. I need 105 ums in this exam for my A overall in chem, hopefully I can pull this off

    If anyone has any questions, just post them here, the others or myself will be able to help.

    :yy:
    Um.. how much would that make if we're considering out of 80, and not 120?
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    (Original post by Zoeyyy)
    Um.. how much would that make if we're considering out of 80, and not 120?
    We can't say yet, because the grade boundaries haven't been out yet!!!




    I need to aim for 70/80 marks, to be guaranteed of 105, but depending on the grade boundaries of course!
    Offline

    0
    ReputationRep:
    (Original post by James A)
    We can't say yet, because the grade boundaries haven't been out yet!!!




    I need to aim for 70/80 marks, to be guaranteed of 105, but depending on the grade boundaries of course!
    Yeah I meant the "estimated" value haha well good luck
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    (Original post by Zoeyyy)
    Yeah I meant the "estimated" value haha well good luck
    Thanks

    Wbu? You in year 12?
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.