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) \(\mathrm{HSe}^{-}\), (d) \(\mathrm{HSeO}_{3}^{-}\).

Short answer

The selenium-containing ions can be named as follows: (a) \(\mathrm{SeO}_{4}{ }^{2-}\) is selenate, (b) \(\mathrm{Se}^{2-}\) is selenide, (c) \(\mathrm{HSe}^{-}\) is hydrogen selenide, and (d) \(\mathrm{HSeO}_{3}^{-}\) is hydrogen selenite.

Step-by-step solution

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

This ion is analogous to the sulfate ion, which is composed of sulfur, oxygen, and has a 2- charge. To name this ion, we will replace the "sulf" in "sulfate" with "selen," signifying the presence of selenium instead of sulfur. Hence, the name of the ion \(\mathrm{SeO}_{4}{ }^{2-}\) is selenate.

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

In \(\mathrm{Se}^{2-}\), selenium acquires a 2- charge. Similarly, sulfur acquires a 2- charge in its sulfide ion (\(\mathrm{S}^{2-}\)). To name this ion, we simply replace "sulf" with "selen" and keep the "ide" ending, identifying it as a simple ion. So, the name of the ion \(\mathrm{Se}^{2-}\) is selenide.

c) Naming \(\mathrm{HSe}^{-}\)

This ion is analogous to the hydrogen sulfide ion, which is composed of hydrogen and sulfur and has a 1- charge. To name this ion, we have to replace the "sulf" in "hydrogen sulfide" with "selen." Thus, the name of the ion \(\mathrm{HSe}^{-}\) is hydrogen selenide.

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

This ion is analogous to the hydrogen sulfite ion, which is composed of hydrogen, sulfur, and oxygen, and has a 1- charge. To name this ion, we replace "sulf" with "selen" and keep the "ite" ending, suggested by its analogy with hydrogen sulfite. Therefore, the name of the ion \(\mathrm{HSeO}_{3}^{-}\) is hydrogen selenite.

Key concepts

Ion Naming

In chemistry, ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net charge. Naming ions is crucial for identifying and understanding the roles they play in chemical reactions.
Anions, which are negatively charged ions, often end with the suffix "-ide" when they are monatomic. For instance, when selenium gains two electrons, it becomes the selenide ion (\(Se^{2-}\)). The name reflects its negative charge and the element involved.
Polyatomic ions, made up of multiple atoms, are named based on the elements and the oxygen content within the ion. If an ion derived from selenium has more oxygen atoms, it often ends in "-ate," like selenate (\(SeO_4^{2-}\)). Less oxygen results in an "-ite" ending, as seen in selenite.

Selenate and Selenide

Selenium compounds, like selenate and selenide, show fascinating properties and analogies with sulfur compounds. Selenate (\(SeO_4^{2-}\)), similar to sulfate, comprises selenium bonded with four oxygen atoms and carries a 2- charge.

On the other hand, selenide (\(Se^{2-}\)) involves only selenium in an anionic form, reflecting its direct presence rather than in combination with other elements. This aligns it with sulfide (\(S^{2-}\)), another simple ion form and shows the elemental behavior when reduced.

Chemical Analogies

Chemical analogies provide a way to predict the behavior and classification of chemical compounds. Selenium is chemically similar to sulfur, as they both belong to group VI of the periodic table.

• Both elements form similar oxyanions, such as selenate for selenium and sulfate for sulfur.
• The naming conventions follow a consistent pattern: substituting sulf- with selen- where appropriate.
• The similarities in their chemical structures allow for predictability in reactions and compounds formed.

This predictability helps in understanding compound formation and their nomenclature.

Trace Nutrients

Trace nutrients are essential elements required by living organisms in minuscule amounts for proper functioning. Selenium is one such nutrient, vital for health yet needed only in tiny quantities.
Selenium is crucial for the functioning of certain enzymes and plays a role in antioxidant activities. While too little can lead to deficiencies, an excess may cause toxicity. It highlights the need for balance in nutrient intake.
Acknowledging selenium as a trace nutrient underpins its presence in biochemical processes, aiding in immune function, reproduction, and even DNA synthesis. Understanding its chemical forms, like selenate and selenide, is important for grasping how it is metabolized and utilized in biological systems.