Problem 32 - Chemistry Matter and Change

Question

Name the following compounds. \(\mathrm{Ag}_{2} \mathrm{CrO}_{4}\)

Step-by-Step Solution

Answer

Silver Chromate

Step 1: Identify the Ions

First, identify the ions in the compound \( \mathrm{Ag}_{2} \mathrm{CrO}_{4} \). The compound is composed of \( \mathrm{Ag}^+ \) ions and \( \mathrm{CrO}_4^{2-} \) ions. \( \mathrm{Ag}^+ \) is the silver ion and \( \mathrm{CrO}_4^{2-} \) is the chromate ion.

Step 2: Name the Cation

The cation in this compound is \( \mathrm{Ag}^+ \), which is silver. Therefore, the cation is named 'Silver.'

Step 3: Name the Anion

The anion in this compound is \( \mathrm{CrO}_4^{2-} \), which is chromate, a polyatomic ion. Therefore, the anion is named 'Chromate.'

Step 4: Combine the Names

Combine the names of the cation and anion to form the compound's name. Since there are no additional rules needed for ionic compounds with these specific ions, the name is 'Silver Chromate.'

Key Concepts

Ionic Compounds

Ionic compounds are formed when positive and negative ions attract each other to form a neutral compound. Whether it's common table salt or more complex compounds, they all rely on the balance of charges between ions. In an ionic compound, there is always a metal element (which forms a positive ion) and a non-metal element or group of elements (which forms a negative ion).

Here are some key aspects of ionic compounds:

• **Structure:** They typically form a lattice structure, where ions are arranged in a repeating three-dimensional pattern.
• **Bond Formation:** The bond between ions is called an ionic bond, which is a result of the electrostatic attraction between oppositely charged ions.
• **Properties:** Due to their structure, ionic compounds usually have high melting and boiling points. They also conduct electricity when melted or dissolved in water because the ions are free to move.

The formula of an ionic compound is written with the cation (positive ion) first and the anion (negative ion) second, reflecting the compound’s charge-neutral status. Understanding the behavior of ionic compounds is fundamental to mastering chemical nomenclature.

Polyatomic Ions

Polyatomic ions are ions composed of more than one atom. They function as a single charged entity and are a crucial part of the study of chemistry. Unlike simple ions that consist of only one element (like sodium or chloride ions), polyatomic ions are composed of different elements bonded together.

Some important facts about polyatomic ions include:

• **Composition:** Polyatomic ions are made of two or more atoms that are tightly bonded, but they have an overall charge due to the loss or gain of electrons.
• **Examples:** Some common polyatomic ions include sulfate (\( ext{SO}_4^{2-}\)), nitrate (\( ext{NO}_3^{-}\)), and, as seen in our exercise, chromate (\( ext{CrO}_4^{2-}\)).
• **Naming Conventions:** The names of polyatomic ions often end in "-ate" or "-ite," with "-ate" usually indicating a higher number of oxygen atoms than "-ite."

Remembering the composition and charge of polyatomic ions is essential when dealing with ionic compounds that include polyatomic ions. This knowledge helps predict how compounds are named and written.

Silver Chromate

Silver chromate is an example of an ionic compound that involves a transition metal and a polyatomic ion. In \( ext{Ag}_2 ext{CrO}_4\), the compound is made of silver ions (\( ext{Ag}^+\)) and chromate ions (\( ext{CrO}_4^{2-}\)). The formulation of this compound reflects the following rules of ionic bonding:

• **Neutral Charge:** The charges of the ions within the compound balance each other out. Silver has a +1 charge, while the chromate ion has a -2 charge. Thus, two silver ions balance with one chromate ion to keep the compound neutral.
• **Naming the Compound:** To name this compound, simply combine the name of the cation (Silver) with the name of the anion (Chromate), resulting in "Silver Chromate."
• **Uses and Characteristics:** Silver chromate is known for its distinctive reddish-brown color and is often used in qualitative inorganic analysis to identify the presence of chloride ions.

Understanding how to name compounds such as silver chromate is crucial for students learning chemical nomenclature. It highlights the importance of recognizing both simple and polyatomic ions in formulas.