Book cover for General Chemistry: Principles and Modern Applications

General Chemistry: Principles and Modern Applications

Ralph H. Petrucci, F. Geoffrey Herring, Jeffry D. Madura, Carey Bissonnette

ISBN #9780132931281

11th Edition

3,230 Questions

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293,395 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter provides a comprehensive overview of chemical compounds by distinguishing between molecular and ionic compounds, and by illustrating multiple modes of representing chemical formulas—empirical, molecular, and structural. Emphasis is placed on the significant role of the mole concept in converting between mass and moles, calculating molar mass, formula units, and percent composition. Additionally, understanding oxidation states is critical for proper nomenclature and accurate chemical analysis. Mastery of these fundamental concepts lays the groundwork for advanced stoichiometric calculations and in-depth chemical studies.

Learning Objectives

1

Differentiate between molecular and ionic compounds.

2

Represent chemical compounds using empirical, molecular, and structural formulas.

3

Apply the mole concept to calculate molar mass, formula units, and percent composition.

4

Determine oxidation states and properly name both organic and inorganic compounds.

Key Concepts

CONCEPT

DEFINITION

Molecular Compound

A chemical compound formed when two or more atoms share electrons through covalent bonds.

Ionic Compound

A compound consisting of positively and negatively charged ions held together by electrostatic forces.

Empirical Formula

The simplest whole-number ratio of the elements in a compound.

Molecular Formula

A formula that shows the actual number of each type of atom present in a molecule.

Structural Formula

A representation of a molecule that shows how the atoms are arranged and bonded together.

Mole Concept

A fundamental concept in chemistry that relates the mass of a substance to the number of particles (atoms, molecules, ions) using Avogadro’s number.

Molar Mass

The mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Percent Composition

The percentage by mass of each element in a compound.

Oxidation State

A number that represents the total number of electrons that an atom gains or loses when forming chemical compounds.

Example Problems

Example 1

Refer to the color scheme given in Figure $3-3,$ and give the molecular formulas for the molecules whose balland-stick models are given here.

Example 2

Give the molecular formulas for the molecules whose ball-and-stick models are given here. Refer to the color scheme in Figure $3-3$

Example 3

Give the structural formulas of the molecules shown in Exercise $1(\mathbf{b}),(\mathrm{d}),$ and $(\mathrm{e})$.

Example 4

Give the structural formulas of the molecules shown in Exercise $2(\mathrm{b}),(\mathrm{d}),$ and $(\mathrm{e})$

Example 5

Calculate the total number of (a) atoms in one molecule of trinitrotoluene (TNT), $\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{2}\left(\mathrm{NO}_{2}\right)_{3}$ (b) atoms in $0.00102 \mathrm{mol} \mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{4} \mathrm{CH}_{2} \mathrm{OH}$ (c) $\mathrm{F}$ atoms in $12.15 \mathrm{mol} \mathrm{C}_{2} \mathrm{HBr} \mathrm{ClF}_{3}$
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Step-by-Step Explanations

QUESTION

How do you calculate the percent composition of an element in a compound given its formula?

STEP-BY-STEP ANSWER:

Step 1: Determine the molar mass of the compound by summing the atomic masses of all atoms in the formula.
Step 2: Identify the total mass of the element of interest in one mole of the compound (number of atoms times atomic mass).
Step 3: Use the formula: Percent Composition = (Mass of element in one mole of compound / Total molar mass of compound) x 100.
Final Answer: Compute the percentage to find the elemental composition by mass.

Percent Composition Calculation

QUESTION

How can you derive a molecular formula from an empirical formula if the molar mass of the compound is known?

STEP-BY-STEP ANSWER:

Step 1: Calculate the empirical formula mass by adding the masses of the elements in the empirical formula.
Step 2: Divide the molar mass of the compound by the empirical formula mass to find the multiplication factor.
Step 3: Multiply the subscripts in the empirical formula by the factor to obtain the molecular formula.
Final Answer: The resulting formula represents the actual number of atoms in a molecule.

Molecular Formula Determination

QUESTION

How do you assign oxidation states to atoms in a compound?

STEP-BY-STEP ANSWER:

Step 1: Use known oxidation rules (e.g., oxygen is typically -2, hydrogen +1) as a guide.
Step 2: For a neutral compound, ensure the sum of oxidation states equals zero; for ions, equals the ion charge.
Step 3: Solve for unknown oxidation states using algebraic methods.
Final Answer: Each atom’s oxidation state is assigned based on the rules and the overall charge balance.

Oxidation State Calculation

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Common Mistakes

  • Confusing the empirical formula with the molecular formula, leading to incorrect calculations.
  • Overlooking the proper use of oxidation state rules, especially in complex ions or compounds.
  • Misapplying the mole concept by not converting units correctly, resulting in errors in molar mass computations.
  • Ignoring the differences in representation (empirical vs. structural) which can lead to misinterpretation of a compound's structure.
  • Failing to properly balance chemical formulas when determining percent composition or formula units.