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Ch.2 - Atoms, Molecules & Ions
All textbooksMcMurry 8th EditionCh.2 - Atoms, Molecules & IonsProblem 155
Chapter 2, Problem 155

What are the formulas of the compounds formed from the following ions? (a) Na+ and NO3- (b) K+ and SO42- (c) Sr2+ and Cl-

Verified step by step guidance
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Step 1: Identify the charges on each ion. For (a) Na+ has a charge of +1 and NO3- has a charge of -1. For (b) K+ has a charge of +1 and SO42- has a charge of -2. For (c) Sr2+ has a charge of +2 and Cl- has a charge of -1.
Step 2: Determine the ratio of ions needed to balance the charges. For (a), since both ions have charges of +1 and -1, they combine in a 1:1 ratio. For (b), since K+ is +1 and SO42- is -2, two K+ ions are needed to balance one SO42- ion. For (c), since Sr2+ is +2 and Cl- is -1, two Cl- ions are needed to balance one Sr2+ ion.
Step 3: Write the chemical formula by combining the ions in the ratio determined. For (a), the formula is NaNO3. For (b), the formula is K2SO4. For (c), the formula is SrCl2.
Step 4: Ensure that the total positive charge equals the total negative charge in each compound. For (a), Na+ and NO3- each have charges that cancel each other out. For (b), 2 K+ ions (2 x +1) balance the -2 charge of SO42-. For (c), 1 Sr2+ ion (+2) balances with 2 Cl- ions (2 x -1).
Step 5: Verify that the formulas are written in the simplest whole number ratio of ions. For (a) NaNO3, (b) K2SO4, and (c) SrCl2, all formulas are already in their simplest form.

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) bond together through electrostatic forces. The overall charge of the compound must be neutral, meaning the total positive charge from cations must balance the total negative charge from anions. Understanding how to combine these ions based on their charges is essential for determining the correct formulas of the resulting compounds.
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Charge Balance

Charge balance is a fundamental principle in forming ionic compounds, where the sum of the positive charges must equal the sum of the negative charges. For example, if a cation has a charge of +1 and an anion has a charge of -1, they combine in a 1:1 ratio. In cases where the charges differ, such as +2 and -2, the ions will also combine in a 1:1 ratio, while a +1 cation with a -2 anion would require two cations to achieve charge neutrality.
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Common Ions and Their Charges

Familiarity with common ions and their respective charges is crucial for predicting the formulas of ionic compounds. For instance, sodium (Na+) has a +1 charge, nitrate (NO3-) has a -1 charge, potassium (K+) has a +1 charge, sulfate (SO42-) has a -2 charge, strontium (Sr2+) has a +2 charge, and chloride (Cl-) has a -1 charge. Recognizing these ions and their charges allows for the correct assembly of ionic formulas based on charge balance.
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Related Practice
Textbook Question

Give systematic names for the following compounds: (f) (NH4)2SO4

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Textbook Question

Name the following ions: (a) Ba2+ (b) Cs+ (c) V3+ (d) HCO3- (e) NH4 (f) Ni2+ (g) NO2- (h) ClO2- i) Mn2+ (j) ClO4-

Textbook Question

What are the formulas of the compounds formed from the following ions? (a) Ca2+ and Br- (b) Ca2+ and SO42- (c) Al3+ and SO42-

Textbook Question
Ammonia (NH3) and hydrazine (N2H4) are both compounds of nitrogen and hydrogen. Based on the law of multiple pro-portions, how many grams of hydrogen would you expect 2.34 g of nitrogen to combine with to yield ammonia? To yield hydrazine?