Is the Bond Angle of PH3 (Phosphine) 107 degrees?

Alcohol5%

Long pair on top pushing the hydrogens down?

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Reply 1

Magician

Alcohol5%

Long pair on top pushing the hydrogens down?

yes it will be.

Reply 2

Alcohol5%

Just found that it's 94 degrees?

How can you have a good calculated guess at bond angles?

Reply 3

Magician

Alcohol5%

Just found that it's 94 degrees?

How can you have a good calculated guess at bond angles?

The shape is pyramidal (with 1 lone pair and 3 bonding pairs) so it will be 107 deg.

you cant really guess the bond angles as they are pretty close values. You'll just have to memorize them (or have a graphical calculator where you can store them :P)

Reply 4

violet

Mathemagician

(or have a graphical calculator where you can store them :P)

Graphical calcs can do that?? :eek:

I want one!

Reply 5

Alcohol5%

I believe that NH3 with 1 lone pair is 107 degrees.

H2O with 2 lone pairs is 105 degrees

And something like methane, all bonded pairs is 109.5 degrees.

Reply 6

Magician

Alcohol5%

I believe that NH3 with 1 lone pair is 107 degrees.

H2O with 2 lone pairs is 105 degrees

And something like methane, all bonded pairs is 109.5 degrees.

I'd say 104 deg for H2O. My book says rest are fine :smile:

Reply 7

violet

I learnt water as 104.5
But normally your answer has to be within a small range so it can be like 2 degrees out either way (ish)

Reply 8

Alcohol5%

There has to be some small margin of error. it's not like you can measure these things with a protractor.

Reply 9

Alcohol5%

So if NH3 is 107 degrees, can we say that PH3 is too?

Yep, PH3 is defo 107

i reckon unit2 is more easier than unit 1 for edexcel chem, hu finks so as well?

Reply 12

Alcohol5%

I do EdExcel, but nuffield, so no i think its harder

Reply 13

Alcohol5%

But, check this link which shows that phosphine has a bond angle of 94 degrees.

http://en.wikipedia.org/wiki/Phosphine

Reply 14

violet

Alcohol5%

But, check this link which shows that phosphine has a bond angle of 94 degrees.

http://en.wikipedia.org/wiki/Phosphine

strange!
But i think you just have to know its 107 like ammonia. Then in like 5 years time you learn that it wasnt that and they just simplified it for you.. Chemistry's like that!

Reply 15

Alcohol5%

yea, i remember when we did sub shells, it told us that wot we had learn previously about shell construction was all wrong.

Yeh, exactly!

you cannot extrapolate the VSEPRT to other molecules such as PH3 simply because the greater size of the phosphorus atom basically affects the inter electron pair repulsion.

It's all very well to say that NH3 is 107º therefore PH3 will be as also - it just isn't.. there are other factors to consider such as the polarised nature of the N-H bond when compared to the P-H bond. The H-P-H bond angle is 93.7º even though it is pyramidal

This also applies to H2S and H2O - they do not have the same bond angle.

The VSEPRT does not predict bond angles , rather it explains them based on some rather simplistic and easily understood "rules"

Just learn the simple molecules H2O, NH3, CH4, XeF4, etc but do not be at all surprised by seemingly similar molecules with very different bond angles.

Reply 18

violet

I was taught PH3 was an example of a 107 degree bond angle though..

Reply 19

charco

Study Forum Helper

violet

I was taught PH3 was an example of a 107 degree bond angle though..

you were taught wrong either to make your life less complicated ...
or because your teacher had been taught that way!

But it still demonstrates the basic proposal of the VSEPRT which is that the lone pair has a greater repulsive effect on the bonding pairs - it's just that in the case of PH3 this effect is even more pronounced.