usernamenew
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suggest a value for the F-N-F bond angle in NHF2, the answer is 107 but why?
I tried working out the number of bonding pairs and lone pairs but I cant do it when theres more than 2 different atoms involed?
if it was NF2 then I could do it but not when theres an extra atom
how am i suposed to do this question, do i ffocus only on the F-N-F - bond or the whole molecule
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dhruvap
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NHF2 is the molecule, draw it out. Nitrogen is the central atom, it has 5 outer electrons, 3 of which form covalent bond with H and x2 F. This leaves you with one lone pair. As a result you get a trigonal pyramidal shape. The one lone pair on the top has greater repulsion than the bonding pairs, as a result the normal tetrahedral angle which is 109.5 is reduced to 107 (-2.5). As a rule of thumb you -2.5 for every lone pair you have.

You do consider the whole molecule shape however as the question asks for the F-N-F angle you can try image this as one side of pyramid, its asking you to find the angle from the top corner.

Hope that helped.
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usernamenew
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(Original post by dhruvap)
NHF2 is the molecule, draw it out. Nitrogen is the central atom, it has 5 outer electrons, 3 of which form covalent bond with H and x2 F. This leaves you with one lone pair. As a result you get a trigonal pyramidal shape. The one lone pair on the top has greater repulsion than the bonding pairs, as a result the normal tetrahedral angle which is 109.5 is reduced to 107 (-2.5). As a rule of thumb you -2.5 for every lone pair you have.

You do consider the whole molecule shape however as the question asks for the F-N-F angle you can try image this as one side of pyramid, its asking you to find the angle from the top corner.

Hope that helped.
thank u. how do we know that 3 covalent bonds form with H, if it doent use H3 in the formula, and is there 1 lone pair because when u draw the molecule out, the N is bonded to 1 H and 2F so there is 1 bond missing?? also, isnt trigonal pyramidal 3bonding pairs and 1 lone pair so does that mean there are 4 electron pairs in total and that u always do 109.5 -2.5 for a trigonal pyrimidal? sorry for asking so many questions, hope u dont mindnd
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dhruvap
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(Original post by usernamenew)
thank u. how do we know that 3 covalent bonds form with H, if it doent use H3 in the formula, and is there 1 lone pair because when u draw the molecule out, the N is bonded to 1 H and 2F so there is 1 bond missing?? also, isnt trigonal pyramidal 3bonding pairs and 1 lone pair so does that mean there are 4 electron pairs in total and that u always do 109.5 -2.5 for a trigonal pyrimidal? sorry for asking so many questions, hope u dont mindnd
I think I might've confused you. As there is one H atom and 2 F atoms, in total there are 3 covalent bonds. So nitrogen which has 5 electrons shares 3 of its electrons with 1 H and 2 F. This leaves one lone pair (5-3 = 2). This is what the shape looks like:

https://chem.libretexts.org/LibreTex...s_of_Molecules

The shape has different names : Pyramidal, trigonal pyramidal and you can also get away with tetrahedral. For every lone pair you have in a molecule with a tetrahedral shape you -2.5. e.g. H20 has 2 lone pairs on Oxygen as a result is has the bond angle 104.5 (109.5 - 5).
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usernamenew
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(Original post by dhruvap)
I think I might've confused you. As there is one H atom and 2 F atoms, in total there are 3 covalent bonds. So nitrogen which has 5 electrons shares 3 of its electrons with 1 H and 2 F. This leaves one lone pair (5-3 = 2). This is what the shape looks like:

https://chem.libretexts.org/LibreTex...s_of_Molecules

The shape has different names : Pyramidal, trigonal pyramidal and you can also get away with tetrahedral. For every lone pair you have in a molecule with a tetrahedral shape you -2.5. e.g. H20 has 2 lone pairs on Oxygen as a result is has the bond angle 104.5 (109.5 - 5).
thank u so much now i get it
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dhruvap
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(Original post by usernamenew)
thank u so much now i get it
:banana:
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username2752874
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(Original post by usernamenew)
suggest a value for the F-N-F bond angle in NHF2, the answer is 107 but why?
I tried working out the number of bonding pairs and lone pairs but I cant do it when theres more than 2 different atoms involed?
if it was NF2 then I could do it but not when theres an extra atom
how am i suposed to do this question, do i ffocus only on the F-N-F - bond or the whole molecule
Think of NH3.

Same number of bonds so same geometry.

Just like H2S is 104 degrees like water
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