Question

Write a formula for the ionic compound that forms between each pair of elements. \(\begin{array}{ll}{\text { a. silver and chlorine }} & {\text { b. sodium and sulfur }} \\ {\text { c. aluminum and sulfur }} & {\text { d. potassium and chlorine }}\end{array}\)

Short answer

a. AgCl, b. Na2S, c. Al2S3, d. KCl

Step-by-step solution

Determine the Charges

Identify the charge of each ion formed by the given elements. Silver typically forms a +1 cation (Ag+), chlorine forms a -1 anion (Cl-), sodium forms a +1 cation (Na+), sulfur forms a -2 anion (S^2-), aluminum forms a +3 cation (Al^3+), and potassium forms a +1 cation (K+).

Combining Ions for Silver and Chlorine

Combine the silver cation and the chlorine anion in a ratio that balances the overall charge. Since both have charges of equal magnitude and opposite signs, they will combine in a 1:1 ratio to form AgCl.

Combining Ions for Sodium and Sulfur

Combine the sodium cation and the sulfur anion in a ratio that balances the overall charge. Two sodium cations will combine with one sulfur anion to form Na2S.

Combining Ions for Aluminum and Sulfur

Combine the aluminum cation and the sulfur anion in a ratio that balances the overall charge. Two aluminum cations will combine with three sulfur anions to form Al2S3.

Combining Ions for Potassium and Chlorine

Combine the potassium cation and the chlorine anion in a ratio that balances the overall charge. Since both have charges of equal magnitude and opposite signs, they will combine in a 1:1 ratio to form KCl.

Key concepts

Ionic Bonding

Ionic bonding is a fundamental chemical process where atoms gain or lose electrons, resulting in the formation of ions. These ions, which are charged particles, come together to form a neutral compound. A key feature of ionic bonding is the transfer of electrons from one atom to another, leading to the formation of positively charged cations and negatively charged anions.

As a simple model to understand ionic bonding, imagine a dance between particles: cations are eager positive dancers and anions are their negative counterparts. When they find each other, they form a strong bond, a stable 'dance pair'. This attraction is due to the opposite charges of the ions involved. When writing chemical formulas, it's this strong electrostatic force between ions that dictates how they come together to create compounds with no overall charge.

Cation and Anion Charges

In the world of chemistry, cation and anion charges are like the rules of a game that dictate how players—ions in this case—interact. Cations are ions with a positive charge which occur when an atom loses one or more electrons. Anions, on the other hand, have a negative charge resulting from the gain of one or more electrons.

Identifying Ion Charges

Many elements tend to form ions with specific charges. For instance, Group 1 elements (like sodium and potassium) form +1 cations while Group 2 elements (like magnesium and calcium) form +2 cations. On the anion side, Group 17 elements (like chlorine) typically form -1 anions, and the oxygen family (Group 16) forms -2 anions. It's crucial to know these common charges to predict how atoms will combine in ionic compounds.

Chemical Formula Determination

Determining the chemical formula of an ionic compound is like solving a puzzle where the goal is to balance the positive and negative charges. This ensures that the total charge in the compound is zero, following the principle of charge neutrality.

Steps in Formulation

First, the charge on each ion is established, as seen in our previously given exercise. After recognizing their charges, you combine the ions in proportions that counterbalance each other's charges. For example, a cation with a +3 charge will couple with three anions of -1 charge to neutralize the overall charge.

The formula reflects the smallest whole-number ratio of ions. In some cases, you'll use a simple 1:1 ratio, as in NaCl or KCl, while others may require a 2:3 ratio, such as in Al2S3. It is important for students to practice with multiple examples, as fluency in this process is critical in chemistry.