Boiling points of compounds of group 15, 16 and 17 elements?

Question

Some boiling points for hydrogen compounds of Group 15, 16 and 17 elements in degrees celsius:

Group 15
PH3 (g)-87
AsH3 (g)-55
SbH3 (g)-17

Group 16
H2S (g)-61
H2Se (g)-42
H2Te (g)-2

Group 17
HCl (g)-85
HBr (g)-67
HI (g)-36

I don't understand the trend between groups... Group 16 is highest, then Group 15, and Group 17 is the lowest? That does not fit into any pattern, whether I think of polarity, molecular size etc.? Can someone explain why this is so?

Answer 1

Hmmm.. The one affecting the boiling point is the intermolecular force..
As you can see, most of the compound here is polar.

Therefore all you have to do is if the compound is consisted only of 2 elements (Group 17), you'll have to calculate the electronegativity difference. The more difference between them, the boiling will increase as well.

If there is more than 2 atoms in a molecule, you'll have to see the dipole moment magnitude (a.k.a polarity). The higher the magnitude, the higher the boiling point will be.


peace
vixklen

Answer 2

try looking at the charge differences between the elements. the greater the difference the higher amoung of heat it needs to boil or break some bons essentially, but I don know if that the pattern your looking for. Also, when electronegativity goes down, so does BP.