Turn on thread page Beta
    • Thread Starter
    Offline

    15
    ReputationRep:
    My teacher made us an online AS revision quiz, which I think is a nice way to set homework, but I think one of the answers may have been wrong. I'm not trying to correct my teacher - she definitely knows best - but I just need someone to explain to me why I got the question wrong.

    Name:  why.PNG
Views: 43
Size:  52.0 KBHopefully you can see the image!

    Bond angles:
    NH3 = 107
    CH4 = 109.5
    H20 = 104.5
    CO2 = 180
    (excuse the lack of subscript formatting)

    107 < 109.5 < 180
    Those molecules (option C) are in order of increasing bond angle.

    107 < 109.5 > 104.5
    These (option D) are NOT.

    Why is option D the correct answer? What did my teacher mean by 'remember lone pairs'????

    Thanks!
    • Community Assistant
    • Study Helper
    Online

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by JustJusty)
    My teacher made us an online AS revision quiz, which I think is a nice way to set homework, but I think one of the answers may have been wrong. I'm not trying to correct my teacher - she definitely knows best - but I just need someone to explain to me why I got the question wrong.

    Name:  why.PNG
Views: 43
Size:  52.0 KBHopefully you can see the image!

    Bond angles:
    NH3 = 107
    CH4 = 109.5
    H20 = 104.5
    CO2 = 180
    (excuse the lack of subscript formatting)

    107 < 109.5 < 180
    Those molecules (option C) are in order of increasing bond angle.

    107 < 109.5 > 104.5
    These (option D) are NOT.

    Why is option D the correct answer? What did my teacher mean by 'remember lone pairs'????

    Thanks!
    You are correct, your teacher has made a mistake.

    I also make online m/C tests and from time to time I put the wrong answer in. It's usually because during the programming you are looking at code, not at chemistry and it's easy to make a mistake.
    Offline

    13
    ReputationRep:
    (Original post by JustJusty)
    My teacher made us an online AS revision quiz, which I think is a nice way to set homework, but I think one of the answers may have been wrong. I'm not trying to correct my teacher - she definitely knows best - but I just need someone to explain to me why I got the question wrong.

    Name:  why.PNG
Views: 43
Size:  52.0 KBHopefully you can see the image!

    Bond angles:
    NH3 = 107
    CH4 = 109.5
    H20 = 104.5
    CO2 = 180
    (excuse the lack of subscript formatting)

    107 < 109.5 < 180
    Those molecules (option C) are in order of increasing bond angle.

    107 < 109.5 > 104.5
    These (option D) are NOT.

    Why is option D the correct answer? What did my teacher mean by 'remember lone pairs'????

    Thanks!
    You are correct. Because of the VSEPR theory, the CO2 has a linear molecular geometry (AB2E0) (180º), the H2O is an special case because the couples of electrons without sharing exercise a repulsion that avoids the formation of a tetrahedron (109,5 º). Therefore, the bond angle of the H2O is 104,5º. The bond angle of the CH4 is also correct because it has a tetrahedral molecular geometry. Finally, the bond angle of the NH3 is also correct, because NH3 has trigonal pyramidal molecular geometry (107º).

    Maybe your teacher made a mistake while she was writting the answer of that question. The best thing to do is to talk about this with your teacher (without saying that she was wrong hahahahha)

    I hope that my answer will be useful for you
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by charco)
    You are correct, your teacher has made a mistake.

    I also make online m/C tests and from time to time I put the wrong answer in. It's usually because during the programming you are looking at code, not at chemistry and it's easy to make a mistake.
    (Original post by Alextox)
    You are correct. Because of the VSEPR theory, the CO2 has a linear molecular geometry (AB2E0) (180º), the H2O is an special case because the couples of electrons without sharing exercise a repulsion that avoids the formation of a tetrahedron (109,5 º). Therefore, the bond angle of the H2O is 104,5º. The bond angle of the CH4 is also correct because it has a tetrahedral molecular geometry. Finally, the bond angle of the NH3 is also correct, because NH3 has trigonal pyramidal molecular geometry (107º).

    Maybe your teacher made a mistake while she was writting the answer of that question. The best thing to do is to talk about this with your teacher (without saying that she was wrong hahahahha)

    I hope that my answer will be useful for you
    Thanks! I thought so, just wanted to make sure I wasn't missing something major. Hopefully someone else will bring it up. I'm sure it's really easy to make mistakes, and some teachers are so overworked that I'm surprised they don't make more of them.
    Offline

    13
    ReputationRep:
    (Original post by JustJusty)
    Thanks! I thought so, just wanted to make sure I wasn't missing something major. Hopefully someone else will bring it up. I'm sure it's really easy to make mistakes, and some teachers are so overworked that I'm surprised they don't make more of them.
    You're welcome
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 10, 2017
Poll
Do you think parents should charge rent?

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

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