Write the chemical formula for hydrogen sulfide - Leaving Cert Chemistry - Question a - 2007

In the dot and cross diagrams for hydrogen sulfide:

• Each hydrogen atom is represented with its own electron (cross or dot).
• The sulfur atom shares pairs of electrons with each hydrogen atom.

The diagram can be presented as:

  H   H
  •   •
   \ / 
    S
  ••••

This shows that sulfur has two bonding pairs of electrons shared with the two hydrogen atoms, and there are non-bonding (lone) pairs present as well.

I would expect the hydrogen sulfide molecule to be non-linear in shape. This is due to the presence of two non-bonding (lone) pairs of electrons on the sulfur atom, which affect the molecular geometry. The four electron pairs in the valence shell of the sulfur atom (two bonding pairs and two lone pairs) result in a bent structure according to VSEPR theory.

The difference in boiling points can be attributed to the types of intermolecular forces present in each substance. Hydrogen sulfide exhibits weak dipole-dipole forces due to the polar nature of the H-S bond, and also experiences London dispersion forces. In contrast, water has strong hydrogen bonds, which significantly increase its boiling point, making it higher than that of hydrogen sulfide. Therefore, the stronger hydrogen bonds in water lead to its higher boiling point.

I would expect hydrogen sulfide to be only slightly soluble in water. While hydrogen sulfide can form weak interactions with water due to its polar nature, it does not form hydrogen bonds like water does. Therefore, the solubility of hydrogen sulfide in water is limited compared to substances that exhibit strong hydrogen bonding.