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Ch.8 - Basic Concepts of Chemical Bonding
Chapter 8, Problem 17a

Predict the chemical formula of the ionic compound formed between the following pairs of elements: (a) Al and Cl

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Identify the charges of the ions formed by each element: Aluminum (Al) typically forms a cation with a charge of +3, while Chlorine (Cl) forms an anion with a charge of -1.
Use the criss-cross method to balance the charges: The charge of the aluminum ion (+3) becomes the subscript for chlorine, and the charge of the chloride ion (-1) becomes the subscript for aluminum.
Write the chemical formula by placing the subscripts after each element symbol: Al will have a subscript of 1 (which is usually omitted), and Cl will have a subscript of 3.
Combine the elements with their respective subscripts to form the chemical formula of the compound.
Ensure the compound is electrically neutral by verifying that the total positive charge equals the total negative charge.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons to achieve full outer electron shells, resulting in the formation of charged ions. Typically, metals lose electrons to become positively charged cations, while nonmetals gain electrons to become negatively charged anions. The electrostatic attraction between these oppositely charged ions forms the ionic compound.
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Charge Balance

In ionic compounds, the total positive charge must balance the total negative charge to create a neutral compound. This involves determining the charges of the ions formed by the elements involved. For example, aluminum (Al) typically forms a +3 cation, while chlorine (Cl) forms a -1 anion, necessitating three chloride ions to balance one aluminum ion.
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Empirical Formula

The empirical formula of an ionic compound represents the simplest whole-number ratio of the ions present. For the compound formed between aluminum and chlorine, the empirical formula is derived from the charge balance, leading to AlCl3, which indicates that one aluminum ion combines with three chloride ions to form a stable ionic compound.
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