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    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
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    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!
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    (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: 29
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.
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    (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: 29
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
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    (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.
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    (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
 
 
 
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