boiling points?

Question

Rank the following compounds in order of increasing boiling points, and describe the intermolecular forces which affect the ranking.

a. H2Se
b. H2S
c. H2Te

Answer 1

H2Se (hydrogen (I) selenide)

Boiling point: -42°C

H2S (hydrogen sulfide)

Boiling point: -60°C

H2Te (hydrogen telluride)

Boiling point: −4 °C

Answer 2

Hi,
I have some interesting facts for you, possibly answering your question.
First a quotation from http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&lis
t_uids=9417954&dopt=Abstract

"Question - Hydrogen bonding with the chalcogens (and the anomolity of water). I have been compelled to understand the specific reasons known to date the anomolity of the unusually high boiling and freezing points of water (H2O) compared to the other chalcogens (H2S, H2Se, H2Te).
I know from previous questions you have answered and other web sites these particular patterns:

Boiling points: H20= 100C, H2S= -61C, H2Se= -45C, H2Te= -2C

Bonding Angles: H2O=104.5, H2S=92.2, H2Se=91, H2Te=89.5, H2Po=?


However, this web site source suggested that H2Po fourfold clusters is similar to H2Te (whatever pattern that
represents?)
The bonding angles follow a descending pattern. Why do the boiling points follow an ascending pattern AFTER the unusual boiling point of simple H2O?"

That`s the original quotation.
Let`s have a look at the periodic table of elements.

Important: From the elements S, Se, Te the atom S has the highest and Te the lowest electronegativity (EN). Therefore the interatomar forces are decreasing in this order and Te has the highest boiling point (b.p.). Oxygen by the way is in the table in the same colume as the other 3 elements and has the highest negativity and also the highest boiling point.

So I think we can conclude that the ranking in boiling points is rrelated to the ranking in EN.

In WIKIPEDIA is stated: (http://en.wikipedia.org/wiki/Electronegativity)

"Each element has a characteristic electronegativity ranging from 0 to 4 on the Pauling scale. The most strongly electronegative element, fluorine, has an electronegativity of 3.98 while weakly electronegative elements, such as lithium, have values close to 1. The least electronegative element is francium at 0.7. In general, the degree of electronegativity decreases down each group and increases across the periods, as shown below. Across a period, non-metals tend to gain electrons and metals tend to lose them due to the atom striving to achieve a stable octet. Down a group, the nuclear charge has less effect on the outermost shells. Therefore, the most electronegative atoms can be found in the upper, right hand side of the periodic table, and the least electronegative elements can be found at the bottom left. Consequently, in general, atomic radius decreases across the periodic table, but ionization potential increases.

Summary:

1. The ranking in b.p. is H2Te, H2Se, H2S
2. In general the b.p inreases with the increasing EN (electronegativity)
3. The intermolecular forces are related to the outer electrons. Important is the EN as a result of the electron configuration.
4. In chemical compounds like molecules the difference DeltaEN of the EN of the single atoms are responsible for the strenghts of the bonding.
5. If the difference DeltaEN is greater than 1,7 we call the bond
6. No electronegativity difference between two atoms leads to a pure non-polar covalent bond.
7. A small electronegativity difference leads to a polar covalent bonds.
8. A large electronegativity difference leads to an ionic bond.

If you need to go into more details you have to study orbital concepts and configuration of electzrons in atoms and molecules. You must understand statements like this:

"In an ionic bond, the atoms are bound by attraction of opposite ions, whereas, in a covalent bond, atoms are bound by sharing electrons. In covalent bonding, the molecular geometry around each atom is determined by VSEPR rules, whereas, in ionic materials, the geometry follows maximum packing rules."

I hope, you can get something ouit of my statements. Good luck!

Answer 3

Check out your text - look for periodic trends of Group 6 elements and you'll find this one out.

Example, H2S is a gas at room temperature.... does that tell you something about its bp in relation to the others?