Problem 109 - Chemistry The Central Science In Si Units

Question

Elements in the same group of the periodic table often form oxyanions with the same general formula. The anions are also named in a similar fashion. Based on these observations, suggest a chemical formula or name, as appropriate, for each of the following ions: \((\mathbf{a}) \mathrm{BrO}_{4}^{-},(\mathbf{b}) \mathrm{SeO}_{3}^{2-},(\mathbf{c})\) arsenate ion, (d) hydrogen tellurate ion.

Step-by-Step Solution

Answer

BrO4- is perbromate, SeO3^2- is selenite, arsenate ion is AsO4^3-, hydrogen tellurate ion is HTeO4^-.

Step 1: Identify Patterns in Oxyanions

Elements within the same group of the periodic table can form oxyanions with similar naming conventions and structural formulas. For example, chlorine and bromine are in Group 17, while selenium and sulfur are in Group 16.

Step 2: Suggest Formula or Name for BrO4-

For bromine (Br), the oxyanion with the formula \( ext{BrO}_4^{-}\) is known as perbromate. The naming follows the pattern where the -ate suffix denotes the most common oxyanion, and the per- prefix indicates the ion with one more oxygen atom than the -ate form.

Step 3: Suggest Formula or Name for SeO3^2-

For selenium (Se), the oxyanion with the formula \( ext{SeO}_3^{2-}\) is called selenite. This follows the naming pattern similar to sulfite \( ext{SO}_3^{2-}\), with the -ite suffix indicating one less oxygen atom than the -ate form.

Step 4: Define Arsenate Ion

The arsenate ion for arsenic (As), located in Group 15, has the formula \( ext{AsO}_4^{3-}\). This follows the pattern established by phosphate \( ext{PO}_4^{3-}\) in the same group.

Step 5: Define Hydrogen Tellurate Ion

For tellurium (Te), the most common oxyanion is tellurate, \( ext{TeO}_4^{2-}\). When a hydrogen ion (H) is added to an oxyanion, it becomes a hydrogen ion form of the oxyanion. Therefore, the hydrogen tellurate ion formula is \( ext{HTeO}_4^{-}\).

Key Concepts

Understanding Periodic Table Groups

The periodic table is organized into columns known as groups. Elements within the same group typically exhibit similar chemical behaviors due to their identical number of valence electrons.
Valence electrons determine an element's ability to bond and form compounds. For instance, Group 16, also known as the chalcogens, includes elements like oxygen, sulfur, and selenium.
These elements are known for forming compounds, especially oxyanions, due to their ability to gain electrons easily.
Elements within a group often form oxyanions with similar formulas. With a shared family of oxyanions, this similarity allows us to predict and understand the formulas of these ions. For example, sulfur in Group 16 forms sulfate ions, while selenium forms selenate ions, reflecting consistent behavior across the group.

Mastering Anion Naming Conventions

The naming of oxyanions follows specific conventions, which help in identifying the composition and structure of these ions.
The suffixes -ate and -ite are commonly used, with -ate generally indicating the oxyanion with more oxygen atoms, and -ite having one fewer oxygen atom.

• The prefix per- is used for oxyanions with one more oxygen atom than the -ate form, such as perchlorate (ClO₄⁻) or perbromate (BrO₄⁻).
• The prefix hypo- is used for oxyanions with fewer oxygen atoms than the -ite form.

Learning these prefixes and suffixes allows you to recognize the structure and formula of various oxyanions without memorization. Thus, the arsenate ion is related to phosphate (PO₄³⁻) with a formula AsO₄³⁻.

Deciphering Chemical Formulas

Chemical formulas are the blueprint of a compound, indicating the types and numbers of atoms involved. In the context of oxyanions, this information is key to understanding how atoms are arranged and interact.
The formula for a compound provides clues on its charge, the number of oxygen atoms, and the central atom. For example, in SeO₃²⁻, selenium is the central atom bonded to three oxygen atoms, with an overall charge of -2.
When determining formulas, it's crucial to understand the general patterns and naming conventions for each group. This helps to predict the likely structure and charge for any oxyanion.

Deep Dive into Group 16 Elements

Group 16 consists of nonmetals and metalloids like oxygen, sulfur, selenium, and tellurium. These elements are known for high electronegativities and the ability to form stable compounds.
Oxyanions of these elements, like sulfate and selenate, typically exhibit -ate suffixes, signifying the most common form of their oxyanion.
For tellurium, its common ion is tellurate (TeO₄²⁻), and the hydrogen tellurate ion includes a hydrogen atom, resulting in HTeO₄⁻.
Understanding the properties specific to Group 16 can reveal significant insights into the formation and behavior of their oxyanions, providing a consistent framework for learning chemistry.