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: (a) \(\mathrm{BrO}_{4}^{-}\), (b) \(\mathrm{SeO}_{3}{ }^{2-}\), (c) arsenate ion, (d) hydrogen tellurate ion.

Short answer

(a) \(\mathrm{BrO}_{4}^{-}\): Perbromate (b) \(\mathrm{SeO}_{3}{ }^{2-}\): Selenite (c) Arsenate ion: \(\mathrm{AsO}_{4}{ }^{3-}\) (d) Hydrogen tellurate ion: \(\mathrm{HTeO}_{4}^{-}\)

Step-by-step solution

Identify the group of the element

First, we have to identify to which group the elements in the given ions belong to. For Br (Bromine), it is in group 7A or 17. Se (Selenium) is in group 6A or 16. As (Arsenic) and Te (Tellurium) are in the group 5A or 15 and group 6A or 16, respectively.

Find the similar formula or name for the given ions

Now that we know the group each element belongs to, we'll look at the representative oxyanion formulas within their respective groups and deduce the formula or name as appropriate. (a) For \(\mathrm{BrO}_{4}^{-}\): Since bromine (Br) is in group 7A or 17, it will have a similar formula to the other halogens in this group. Chlorine (Cl) forms the ion \(\mathrm{ClO}_{4}^{-}\) which is called perchlorate. Therefore, the ion \(\mathrm{BrO}_{4}^{-}\) will be called perbromate. (b) For \(\mathrm{SeO}_{3}{ }^{2-}\): Selenium (Se) is in group 6A or 16, so we can look at the oxyanions formed by sulfur (S), which is also in the same group. Sulfur forms the ion \(\mathrm{SO}_{3}{ }^{2-}\), which is called sulfite. Thus, the ion \(\mathrm{SeO}_{3}{ }^{2-}\) will be called selenite. (c) For arsenate ion: Arsenic (As) is in group 5A or 15. We can check the oxyanions formed by phosphorus (P), which is in the same group. Phosphorus forms the ion \(\mathrm{PO}_{4}{ }^{3-}\), which is called phosphate. Therefore, the arsenate ion will have the chemical formula \(\mathrm{AsO}_{4}{ }^{3-}\). (d) For hydrogen tellurate ion: Tellurium (Te) is in group 6A or 16. We can look at the oxyanions formed by selenium (Se), which is also in this group. Selenium forms the hydrogen selenate ion, \(\mathrm{HSeO}_{4}^{-}\). Thus, the hydrogen tellurate ion will have the chemical formula \(\mathrm{HTeO}_{4}^{-}\).

Provide the chemical formula or name as appropriate

For each of the given ions, we have determined the chemical formula or name: (a) \(\mathrm{BrO}_{4}^{-}\): Perbromate (b) \(\mathrm{SeO}_{3}{ }^{2-}\): Selenite (c) Arsenate ion: \(\mathrm{AsO}_{4}{ }^{3-}\) (d) Hydrogen tellurate ion: \(\mathrm{HTeO}_{4}^{-}\)

Key concepts

Understanding the Periodic Table in Relation to Oxyanions

The periodic table is a fundamental tool in the world of chemistry, providing a systematic arrangement of the known chemical elements. When it comes to understanding oxyanions, which are negatively charged polyatomic ions with oxygen, the periodic table is invaluable.

Oxyanions often follow a pattern within a group (vertical columns) on the periodic table. Elements in the same group typically have similar electron configurations and exhibit predictable chemical behaviors, such as forming oxyanions with comparable formulas and charges.
For instance, halogens in group 17 form a series of oxyanions, where bromine can form the perbromate ion (\(\mathrm{BrO}_{4}^{-}\)). This consistency allows us to anticipate the properties and naming of oxyanions even if they're not immediately familiar.

By referring to the periodic table, students can identify which group an element belongs to and use analogies from known oxyanions to predict the formula or derive the name for unknown ones. For example, knowing that sulfur from group 16 forms sulfite (\(\mathrm{SO}_{3}^{2-}\)), we can deduce that selenite will be \(\mathrm{SeO}_{3}^{2-}\) based on selenium's position in the same group.

Decoding Chemical Formulas of Oxyanions

Chemical formulas are a way of representing the composition of a chemical compound using element symbols and numerical subscripts. For oxyanions, understanding their chemical formulas is crucial for recognizing the type of ion and its charge.

A chemical formula gives us specific information. For example, \(\mathrm{AsO}_{4}^{3-}\) tells us that one arsenate ion consists of one arsenic atom and four oxygen atoms, carrying a 3- charge. The subscript '4' indicates the quantity of oxygen atoms, while the superscript '3-' conveys the overall charge of the ion.

Why Does the Charge Matter?

The charge is significant because it affects how the ion interacts with other ions and forms compounds. Oxyanions with different charges can combine with various cations (positively charged ions) to create distinct substances with unique properties and uses.

By accurately reading and interpreting chemical formulas, students can better grasp the nature of the substance and predict how it will behave in chemical reactions.

Ion Naming Conventions

Ion naming conventions are a set of rules used to name ions systematically. These conventions become particularly important when dealing with oxyanions, as they often have similar formulas but differ in the number of oxygen atoms and their respective charges.

To name an oxyanion, we look at the element it is based on and the amount of oxygen present. For instance, the prefix 'per-' and the suffix '-ate' are used for oxyanions with the most oxygen atoms in their series, such as perchlorate (\(\mathrm{ClO}_{4}^{-}\)). When one less oxygen is present, the suffix changes to '-ite', like in chlorite (\(\mathrm{ClO}_{2}^{-}\)).

In some cases, hydrogen or bi- is added at the beginning to denote the presence of an additional hydrogen atom, influencing the ion's charge. Therefore, the hydrogen tellurate ion is written as \(\mathrm{HTeO}_{4}^{-}\), indicating an extra hydrogen compared to the tellurate ion (\(\mathrm{TeO}_{4}^{2-}\)).

Understanding these conventions enables students to identify and communicate about various ions properly and is essential for mastering chemistry nomenclature.