Question

By analogy with phosphorus compounds, name the following: \(\mathrm{Na}_{3} \mathrm{AsO}_{4}, \mathrm{H}_{3} \mathrm{AsO}_{4}, \mathrm{Mg}_{3}\left(\mathrm{SbO}_{4}\right)_{2}\)

Short answer

The short version of the answer is: 1. \(\mathrm{Na}_{3} \mathrm{AsO}_{4}\): Sodium Arsenate 2. \(\mathrm{H}_{3}\mathrm{AsO}_{4}\): Arsenic Acid 3. \(\mathrm{Mg}_{3}\left(\mathrm{SbO}_{4}\right)_{2}\): Magnesium Antimonate

Step-by-step solution

Recognize the main elements and their periodic table positions

Both phosphorus (P) and arsenic (As) are in Group 15 of the periodic table, while antimony (Sb) is in the same group. This means that their chemical behavior is similar and we can use this knowledge to make analogies with phosphorus compounds.

Identify and name the anions in each compound

In each of the given compounds, we have a metal (sodium, hydrogen, or magnesium) and a non-metal element that forms an anion, a negatively charged ion, in the compounds: \(\mathrm{Na}_{3} \mathrm{AsO}_{4}\): Here, AsO4 is an anion, which is analogous to the phosphate (PO4) anion in phosphorus compounds. As the compound ion is arsenate (AsO4)³⁻, we can name it as sodium arsenate. \(\mathrm{H}_{3}\mathrm{AsO}_{4}\): In this case, we have the same arsenate (AsO4)³⁻ anion, but with hydrogen as the cation. Thus, we can name this compound as arsenic acid. \(\mathrm{Mg}_{3}\left(\mathrm{SbO}_{4}\right)_{2}\): Here, the compound ion is antimonate (SbO4)³⁻, which is analogous to the phosphate anion. It forms a compound with magnesium, so we can call it magnesium antimonate.

Combine the metal and the anion names

Now that we have identified and named both the metal and the anion in each compound, we can combine them to give the full name for each compound: 1. \(\mathrm{Na}_{3} \mathrm{AsO}_{4}\): Sodium Arsenate 2. \(\mathrm{H}_{3}\mathrm{AsO}_{4}\): Arsenic Acid 3. \(\mathrm{Mg}_{3}\left(\mathrm{SbO}_{4}\right)_{2}\): Magnesium Antimonate

Key concepts

Group 15 elements

Group 15 of the periodic table, also known as the Nitrogen Group, includes elements that share similar properties. This group consists of nitrogen, phosphorus, arsenic, antimony, and bismuth. These elements typically have five valence electrons, which plays a significant role in their chemical behavior, allowing them to form various covalent bonds.

Common characteristics of Group 15 elements include:

• They usually exhibit oxidation states of -3, +3, and +5.
• The electronegativity decreases as you move down the group, impacting their reactivity and types of compounds they form.
• They often form pnictides when combined with metals, which are compounds containing one member from the nitrogen group and a metal.

Understanding the trends and behaviors of Group 15 elements helps in predicting the properties and reactions of compounds they form, akin to transforming potential reactivity trends seen with phosphorus to other group members like arsenic and antimony.

Anions

Anions are negatively charged ions that form when an atom gains electrons. In chemical compounds, anions are typically combined with cations, which are positively charged. This balance maintains the neutrality of overall ionic compounds, such as salts.

Characteristics of anions include:

• They often gain electrons to achieve a full outer electron shell based on the octet rule, resulting in a stable configuration.
• Anions are usually larger than their neutral atoms due to the addition of extra electrons.
• They move towards the positive electrode, the anode, during electrolysis, which is how they get their name.

In the context of the given exercise, ions like arsenate (\(\text{AsO}_4^{3-}\)) and antimonate (\(\text{SbO}_4^{3-}\)) are both anions. Their ability to form these stable configurations mimics those found in their phosphorus counterparts, such as phosphate.

Phosphate analogs

Phosphate analogs are compounds that resemble phosphate (\(\text{PO}_4^{3-}\)), often with elements that are chemical relatives. For example, arsenic (\(\text{As}\)) and antimony (\(\text{Sb}\)) can create similar structures such as arsenate (\(\text{AsO}_4^{3-}\)) and antimonate (\(\text{SbO}_4^{3-}\)). These compounds have analogous structural and chemical properties.

Important features of phosphate analogs include:

• They often maintain the same tetrahedral geometry, similar to phosphate compounds.
• Analogous chemical reactions and bonding properties exist due to the influence of Group 15 element similarities.
• Phosphate analogs can form essential bioinorganic compounds, making them significant in fields like biochemistry and medicine.

By recognizing arsenate or antimonate as phosphate analogs, we draw parallels that facilitate understanding chemical behavior based on known phosphate chemistry.

Chemical compound naming

Chemical compound naming follows specific conventions that make it easier to identify and communicate about different substances. It usually involves recognizing the types of ions present and how they are arranged.

Here are some guidelines for naming inorganic compounds:

• Name the cation (positive ion) first, followed by the anion (negative ion).
• If the compound includes a metal with multiple oxidation states, specify the state using Roman numerals in parentheses.
• Use prefixes like di-, tri-, or tetra- to indicate the number of atoms if necessary in the case of covalent compounds.

For ionic compounds such as those presented in the exercise, the systematic approach involved:1. Identifying the type of metal (e.g., sodium, magnesium) and its charge.2. Recognizing the type of anion (e.g., arsenate, antimonate), which is often derived from the name of the element forming the central part of the anion.3. Combining these to name the compound entirely, like 'sodium arsenate' (\(\text{Na}_3\text{AsO}_4\)), reflecting the balance of charges within the compound.