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Ch.2 - Atoms, Molecules, and Ions
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
All textbooksBrown 15th EditionCh.2 - Atoms, Molecules, and IonsProblem 62b
Chapter 2, Problem 62b

Predict the chemical formulas of the compounds formed by the following pairs of ions: (b) Fe3+ and O2-

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Identify the charges of the ions: Fe^{3+} has a charge of +3 and O^{2-} has a charge of -2.
To form a neutral compound, the total positive charge must balance the total negative charge.
Determine the least common multiple (LCM) of the charges: The LCM of 3 and 2 is 6.
Calculate the number of each ion needed to achieve charge balance: You need 2 Fe^{3+} ions (2 x +3 = +6) and 3 O^{2-} ions (3 x -2 = -6).
Write the chemical formula by placing the number of each ion as subscripts: Fe_2O_3.

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Key Concepts

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

Ionic Compounds

Ionic compounds are formed when positively charged ions (cations) and negatively charged ions (anions) combine. The overall charge of the compound must be neutral, meaning the total positive charge must balance the total negative charge. Understanding how to combine these ions based on their charges is essential for predicting the correct chemical formula.
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Charge Balance

Charge balance is a fundamental principle in chemistry that dictates how ions combine to form neutral compounds. For example, in the case of Fe3+ (a cation with a +3 charge) and O2- (an anion with a -2 charge), the charges must be balanced to achieve neutrality. This often involves determining the lowest common multiple of the charges to find the correct ratio of ions.
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Chemical Formula Representation

The chemical formula of a compound represents the types and numbers of atoms present in the compound. For ionic compounds, the formula is typically written with the cation first followed by the anion, and subscripts are used to indicate the number of each ion needed to achieve charge balance. For example, the formula for the compound formed by Fe3+ and O2- is Fe2O3, indicating two iron ions and three oxide ions.
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