What are the order of melting points for water, hydrogen sulfide, hydrogen telluride, and hydrogen selenide?

1 Answer
Apr 8, 2017

Answer:

I would guess, #H_2Te# #># #H_2Se# #># #H_2S# #"<<"# #H_2O# with respect to melting point.

Explanation:

I would guess, #H_2Te# #># #H_2Se# #># #H_2S# #"<<"# #H_2O# with respect to melting point.

But as a chemist, as a physical scientist, you are required to interpret data, not remember them. As a matter of fact I do remember the normal boiling points (I will tell you why in a minute), #H_2Te, -2.2# #""^@C#, #H_2Se, -41.3# #""^@C#, and #H_2S#, #-60# #""^@C#. Clearly, the dominant intermolecular force is hydrogen bonding, which is expressed most strongly in #"water"#. Boiling points of the lower hydrides follow the order we would expect for dispersion forces.

When I was much younger, I worked in an inorganic lab whose specialty was inorganic sulfides and selenides. Now you have probably gotten a whiff of #H_2S#, which is pretty nasty. The lower group hydrides, #H_2Te#, and #H_2Se#, are even worse: they smell like dead dogs. Very early in my career I disposed of some selenide residues without proper precautions (i.e. bleaching the residues out). I managed to clear an entire building of students and ancillary staff, and since I did the right thing and put my hand up and copped the blame, my name was mud for the rest of my time in that department. I also found out that #H_2Te#, and #H_2Se# were significantly more toxic than #HC-=N#. At least I didn't kill anyone (including myself).