Question

Oxygen and sulfur have similar chemical properties due to having six valence electrons. Both form molecules with two hydrogen atoms. Surprisingly, water (H2O) is a liquid, yet H2S is a gas, even though sulfur is much larger and heavier than oxygen. Why? Explain fully. (5 points)

Answer 1

Whether a substance is a liquid or gas at a given temperature depends on the attractive forces
between its molecules. H2S is a gas at room temperature and H2O is a liquid because the hydrogen bonds that hold H2O molecules together do not form between H2S molecules. A sulfur atom is much larger than an oxygen atom, and because of its larger size, the outermost electrons are not as strongly attracted to the nucleus of the sulfur atom as they are in an oxygen atom. Consequently, the hydrogen-sulfur bond is much less polar than the hydrogen-oxygen bond. Because of the reduced polarity, the sulfur in a H2S molecule is not strongly attracted to the hydrogen atoms in an adjacent H2S molecule, and hydrogen bonds, which are so predominant in water, do not form.