Question

Selenium, an element required nutritionally in trace quantities, forms compounds analogous to sulfur. Name the following ions: (a) \(\mathrm{SeO}_{4}{ }^{2-}\), (b) \(\mathrm{Se}^{2-}\), (c) HSe, (d) \(\mathrm{HSeO}_{3}^{-}\).

Short answer

(a) tetraoxoselinate(VI), (b) selenide, (c) hydrogen selenide, (d) hydrogen selenite (or biselenite)

Step-by-step solution

Naming (a) \(\mathrm{SeO}_{4}{ }^{2-}\)

: This ion is analogous to sulfate (\(\mathrm{SO}_{4}{ }^{2-}\)). The Se takes the place of S, and it is a tetraoxoselinate(VI) ion. So, the name of this ion is: tetraoxoselinate(VI).

Naming (b) \(\mathrm{Se}^{2-}\)

: This ion is analogous to sulfide (\(\mathrm{S}^{2-}\)). The Se takes the place of S, and it is a selenide ion. So, the name of this ion is: selenide.

Naming (c) HSe

: This compound is analogous to hydrogen sulfide (H\(_2\)S). However, in this compound, we only have one hydrogen atom instead of two. The Se takes the place of S, and it is a hydroselenide ion. So, the name of this molecule is: hydrogen selenide.

Naming (d) \(\mathrm{HSeO}_{3}^{-}\)

: This ion is analogous to hydrogen sulfite or bisulfite (\(\mathrm{HSO}_{3}^{-}\)). The Se takes the place of S, and it is a hydrogen selenite or biselenite ion. So, the name of this ion is: hydrogen selenite (or biselenite).

Key concepts

Nomenclature of Ions

Understanding the nomenclature of ions is crucial in chemistry. It allows us to identify and communicate about different chemical species correctly. An ion is an atom or molecule with an unequal number of protons and electrons, giving it a net charge. For anions (negatively charged ions), the name often ends with the suffix "-ide" or involves the base name plus specific prefixes or suffixes related to the number of oxygens and their oxidation states.
- For example, the ion \( \text{SeO}_4^{2-} \) follows the naming pattern of **tetraoxo-** indicating four oxygen atoms with selenium taking the place of sulfur, resulting in **tetraoxoselinate(VI)**.
- The ion \( \text{Se}^{2-} \) is simply referred to as **selenide** following the pattern of ions like sulfide.

Analogy with Sulfur Compounds

Selenium and sulfur are both part of the chalcogen group in the periodic table, which informs their similarities in forming certain compounds. These analogies are helpful because if you've learned about sulfur compounds, you can apply similar logic to selenium.
- **Sulfur and selenium** form similar ions, like sulfate \( \text{SO}_4^{2-} \) and selenate \( \text{SeO}_4^{2-} \).
- **Chemical behavior** is typically comparable, meaning reactions often proceed similarly.
By creating direct analogies, it simplifies understanding selenium compounds for students familiar with sulfur chemistry.

Selenides

"Selenide" refers to the negative ion \( \text{Se}^{2-} \), analogous to sulfide \( \text{S}^{2-} \). When selenium gains two electrons, it achieves a stable, negatively charged ion, used widely in chemical compounds.
- **Characteristics of selenide ions** include similarities in reactivity and bond formation to sulfide.
- **Naming convention** here follows typical ionic practices: base name plus "-ide" for the sulfide/selenide family.
Recognizing these conventions helps predict reactivity and properties of the compounds.

Hydrogen Selenides

Hydrogen selenide compounds are those that include both hydrogen and selenium, similar to hydrogen sulfide. An example is \( \text{HSe} \), named "hydrogen selenide", analogous to hydrogen sulfide (\( \text{H}_2\text{S} \)).
- **Formation**: Hydrogen selenides typically form when selenium compounds react with hydrogen-containing species.
- **Chemical behavior**: They are often volatile and can be toxic, with distinct smell reminiscent of rotten eggs, similar to hydrogen sulfide.
Understanding the naming and chemistry of hydrogen selenides is key for handling these substances safely and predicting their reactions in chemical equations.