Video: Applying Knowledge of the Oxidation State of Sulfur in H₂S and Bonding between Molecules of H₂S

For statements (I) and (II), state for each if they are true or false. (I) The sulfur atom in an H₂S molecule has a −2 oxidation state. (II) H₂S molecules exhibit strong hydrogen bonding. If both are true, state if (II) is a correct explanation for (I).

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Video Transcript

For statements (I) and (II), state for each if they are true or false. (I) The sulfur atom in an H2S molecule has a minus two oxidation state. (II) H2S molecules exhibit strong hydrogen bonding. If both are true, state if (II) is a correct explanation for (I).

The first part of this question is about the oxidation state of the sulfur atom in the H2S molecule. The oxidation states of a molecule will sum to be the charge of that molecular ion. Since H2S is a neutral chemical species, the oxidation states for hydrogen and sulfur in the molecule should sum to zero. When it’s in a molecular ion, hydrogen usually has an oxidation state of plus one.

Since there are two hydrogen atoms in a molecule of H2S, so far, the hydrogens are giving us an oxidation state of plus two. So, in order for the oxidation states of these hydrogen and sulfur to sum to zero, sulfur must have an oxidation state of minus two. So, statement (I) is true. The sulfur atom in an H2S molecule does have a minus two oxidation state.

Statement (II) of this question is about hydrogen bonding. Hydrogen bonding is an attractive force that occurs between molecules. It occurs when you have hydrogen and then a very highly electronegative element, such as nitrogen, oxygen, or fluorine. When hydrogen is bonded to a highly electronegative element, that element will pull on the electrons on the bond between the two atoms, causing the hydrogen to become partially positively charged and the other atom to become partial negatively charged.

In addition to being partial negatively charged due to the difference in electronegativity, the atom also has lone pairs around it, which means that it has a very high density of negative charge. This creates a very strong, attractive force between this high density of negative charge on one molecule and the partial positively charged hydrogen on another molecule.

The molecule that’s participating in the hydrogen bond that is donating the hydrogen is called the hydrogen bond donor, and the other molecule is called the hydrogen bond acceptor. In this cartoon, I’ve drawn them both to be the same type of molecule. But the hydrogen bond acceptor and the hydrogen bond donor don’t have to be. But in order for all of this to work, the other atom that’s not hydrogen needs to have a lone pair on it and it needs to be highly electronegative.

Unfortunately, the sulfur in H2S isn’t quite electronegative enough. So, H2S molecules do not exhibit strong hydrogen bonding. So, statement (II) is false. Since statement (II) of this question was false, we don’t have to state if (II) is a correct explanation for (I).

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