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Ch.3 - Molecules, Compounds & Chemical Equations
Chapter 3, Problem 33

Write a formula for the ionic compound that forms between each pair of elements. d. aluminum and oxygen

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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, denoted as Al^{3+}, and Oxygen (O) typically forms an anion with a charge of -2, denoted as O^{2-}.
Determine the ratio of ions needed to balance the overall charge of the compound. The goal is to have the total positive charge equal the total negative charge.
To balance the charges, you need two aluminum ions (2 x +3 = +6) and three oxide ions (3 x -2 = -6) to achieve a neutral compound.
Write the formula by placing the cation first followed by the anion, using subscripts to indicate the number of each ion needed. The formula is Al_2O_3.
Ensure the formula is in its simplest form, which it is, as Al_2O_3.

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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. Metals, like aluminum, tend to lose electrons and form cations, while nonmetals, like oxygen, gain electrons to form anions. The electrostatic attraction between these oppositely charged ions leads to the formation of ionic compounds.
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Charge of Ions

The charge of ions is determined by the number of electrons lost or gained by an atom. Aluminum typically loses three electrons to form a +3 cation (Al³⁺), while oxygen gains two electrons to form a -2 anion (O²⁻). Understanding the charges of the ions is crucial for determining the correct ratio of ions in the resulting ionic compound.
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Empirical Formula

The empirical formula of an ionic compound represents the simplest whole-number ratio of the ions present. For aluminum and oxygen, the charges of Al³⁺ and O²⁻ can be balanced by combining two aluminum ions with three oxide ions, resulting in the empirical formula Al₂O₃. This formula indicates that the compound consists of two aluminum ions for every three oxide ions.
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