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Ch.2 - Atoms, Molecules, and Ions
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.2 - Atoms, Molecules, and IonsProblem 62c
Chapter 2, Problem 62c

Predict the chemical formulas of the compounds formed by the following pairs of ions: (c) Na+ and Cr2O72-

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Identify the charges of the ions involved. Sodium (Na+) has a charge of +1, and the dichromate ion (Cr2O72-) has a charge of -2.
Determine the lowest common multiple of the absolute values of the ionic charges to find the simplest ratio of ions that will result in a neutral compound.
Since the charge of Na+ is +1 and the charge of Cr2O72- is -2, the lowest common multiple is 2. This means you need two sodium ions to balance the charge of one dichromate ion.
Write the chemical formula by placing the cation first followed by the anion. Since you need two sodium ions for every dichromate ion, the formula will be Na2Cr2O7.
Check the overall charge of the compound to ensure it is neutral. The total positive charge from the sodium ions (+1 each) and the negative charge from the dichromate ion (-2) should balance out.

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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 cations (positively charged ions) and anions (negatively charged ions) bond together through electrostatic forces. The overall charge of the compound must be neutral, meaning the total positive charge from the cations must balance the total negative charge from the anions.
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Charge Balance

In order to predict the formula of an ionic compound, it is essential to ensure that the charges of the ions balance each other. For example, if a cation has a charge of +1 and an anion has a charge of -2, two cations are needed to balance the charge, resulting in a formula that reflects this ratio.
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Polyatomic Ions

Polyatomic ions are ions that consist of two or more atoms bonded together, carrying a net charge. In this case, Cr2O7^2- is a polyatomic ion known as dichromate, which must be treated as a single unit when combining with other ions to form compounds.
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