Question

Sulfur forms anionic chains of S atoms called polysulfides. Draw a Lewis electron dot structure for the \(\mathrm{S}_{2}^{2-}\) ion. The \(\mathrm{S}_{2}^{2-}\) ion is the disulfide ion, an analogue of the peroxide ion. It occurs in iron pyrites, FeS \(_{2}\).

Short answer

The \\(\mathrm{S}_2^{2-}\\) ion has a Lewis structure with two sulfurs linked by a single bond, each with three lone pairs.

Step-by-step solution

Count Valence Electrons

Sulfur has 6 valence electrons. Thus, each sulfur atom in the ion contributes 6 electrons. Since the ion has an overall two negative charge, we add 2 extra electrons for a total of 6 + 6 + 2 = 14 valence electrons.

Identify Connectivity

The \(\mathrm{S}_{2}^{2-}\) ion consists of two sulfur atoms connected by a single bond, similar to the structure of the peroxide ion.

Draw the Skeleton Structure

Draw the two sulfur atoms connected by a single bond: \\[\mathrm{S} - \mathrm{S}\]\.

Distribute Remaining Electrons

After placing a single bond between the two sulfur atoms (using 2 electrons), distribute the remaining 12 electrons to satisfy the octet rule: place 6 electrons (or 3 lone pairs) around each sulfur atom.

Check Final Structure for Stability

Each sulfur atom has 8 electrons around it, satisfying the octet rule. The Lewis structure should show each atom with a full set of electrons, with the negative charge represented as extra lone pairs.

Key concepts

Understanding Polysulfides

Polysulfides are fascinating chemical compounds that contain chains of sulfur atoms. Each sulfur atom in a polysulfide can connect to another sulfur atom, forming various chain lengths. This ability to form extended chains is due to sulfur's versatile bonding nature. Polysulfides are used in some industrial applications, such as vulcanizing rubber, due to their unique properties. In general, polysulfides vary in their properties depending on the number of sulfur atoms linked together. By studying simple forms like the disulfide ion, scientists can gain insight into the behavior and characteristics of these longer sulfur chains.

Disulfide Ion and Its Significance

The disulfide ion, denoted as \(\mathrm{S}_{2}^{2-}\), consists of two sulfur atoms joined by a single bond. This ion is comparable to the peroxide ion, \(\mathrm{O}_{2}^{2-}\), with the oxygen atoms replaced by sulfur atoms. A disulfide bond is quite vital in biology as it helps stabilize proteins by forming bridges between different parts of a protein molecule. In the context of minerals, disulfide ions are notably present in iron pyrites (also known as fool's gold). This highlights the versatility of sulfur compounds both in biological settings and mineralogical contexts.

The Role of Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical reactions. Understanding how many valence electrons an atom has can help determine how it bonds with other atoms. Sulfur, for instance, has six valence electrons. When forming a disulfide ion, \(\mathrm{S}_{2}^{2-}\), each sulfur adds its six valence electrons, and additional electrons are included due to the ion's negative charge. This brings the total to 14 valence electrons for the disulfide ion. Managing these electrons correctly is vital for drawing the Lewis structure accurately.

The Octet Rule and Its Importance

The octet rule is a guideline in chemistry dictating that atoms tend to adjust their electron configurations to have eight electrons in their valence shell. This rule helps explain the stability of atoms in molecules or ions. In the case of the disulfide ion, \(\mathrm{S}_{2}^{2-}\), each sulfur atom forms a single bond, sharing one pair of electrons. The remainder of the valence electrons are placed as lone pairs around each sulfur atom. This setup ensures that each atom in the ion satisfies the octet rule, thus achieving a state of maximum stability. While some exceptions exist, the octet rule is a helpful tool for predicting how atoms combine and form stable compounds.