Ionic vs. Covalent Compounds and Solubility: Study Notes

Unit: Ionic vs. Covalent Compounds and Solubility

Introduction

This unit explores the differences between ionic and covalent compounds, their properties, and the concept of solubility. Understanding these foundational ideas is essential for classifying matter, predicting compound behavior, and solving problems related to solutions in chemistry.

Classifying Matter

Elements, Atoms, and Compounds

• Element: A pure substance consisting of only one type of atom. Examples: Oxygen (O), Iron (Fe).

• Atom: The smallest unit of an element that retains its chemical properties.

• Compound: A substance formed when two or more elements are chemically bonded together. Example: Water (H2O).

• Mixture: A combination of two or more substances that are not chemically bonded. Example: Salt water.

Classification of Matter: Matter can be classified as elements, compounds, or mixtures. Elements are listed first in a compound's formula.

Ionic and Covalent Compounds

Definitions and Properties

• Ionic Compound: Formed from the electrostatic attraction between positive and negative ions (typically a metal and a nonmetal). They have high melting and boiling points and conduct electricity when dissolved in water.

• Covalent Compound: Formed when two nonmetals share electrons. They generally have lower melting and boiling points and do not conduct electricity in water.

• Metal: Elements that tend to lose electrons and form positive ions (cations).

• Nonmetal: Elements that tend to gain electrons and form negative ions (anions).

Bonding: Ionic bonds result from the transfer of electrons, while covalent bonds result from the sharing of electrons.

Identifying Ionic and Covalent Compounds

Compound	Metal or Nonmetal	Ionic or Covalent Bond?
SO2	Nonmetal	Covalent
F2	Nonmetal	Covalent
MgBr2	Metal + Nonmetal	Ionic
CaO	Metal + Nonmetal	Ionic
H2O	Nonmetal	Covalent
K2O	Metal + Nonmetal	Ionic
AlF3	Metal + Nonmetal	Ionic

Writing Chemical Formulas

• Ionic Compounds: Combine cations and anions in ratios that balance the overall charge. Example: NaCl (Sodium chloride).

• Covalent Compounds: Use prefixes to indicate the number of atoms. Example: CO2 (Carbon dioxide).

Solubility and Solutions

Definitions

• Solubility: The ability of a substance (solute) to dissolve in a solvent to form a homogeneous mixture.

• Solute: The substance being dissolved.

• Solvent: The substance doing the dissolving (often water).

• Saturated Solution: A solution containing the maximum amount of solute that can dissolve at a given temperature.

• Unsaturated Solution: A solution that can dissolve more solute at a given temperature.

• Supersaturated Solution: Contains more dissolved solute than is normally possible at a given temperature.

Solubility of Ionic Compounds

• Ionic compounds are generally soluble in water due to the attraction between ions and water molecules.

• Covalent compounds may be soluble or insoluble depending on their polarity.

Conductivity in Solutions

• Ionic compounds conduct electricity when dissolved in water because they dissociate into ions.

• Covalent compounds typically do not conduct electricity in water.

Concentration of Solutions

Calculating Percent Mass

• Percent by mass: The mass of solute divided by the total mass of solution, multiplied by 100.

$\text{Percent by mass} = \left( \frac{\text{mass of solute}}{\text{mass of solution}} \right) \times 100$

• Example: If 5 grams of MgCl2 are dissolved in 95 grams of water, the percent by mass is: $\left( \frac{5}{5+95} \right) \times 100 = 5\%$

Solubility Curves

Using Solubility Graphs

• Solubility curves show how the solubility of a substance changes with temperature.

• To determine if a solution is saturated, locate the temperature and amount of solute on the graph.

• Compounds above the curve are supersaturated; on the curve, saturated; below the curve, unsaturated.

Summary Table: Ionic vs. Covalent Compounds

Property	Ionic Compounds	Covalent Compounds
Bond Type	Transfer of electrons	Sharing of electrons
Constituent Elements	Metal + Nonmetal	Nonmetal + Nonmetal
Melting/Boiling Point	High	Low to moderate
Electrical Conductivity (in water)	Conducts	Does not conduct
Solubility in Water	Usually soluble	Varies

Key Terms and Definitions

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Cation: A positively charged ion.

• Anion: A negatively charged ion.

• Electronegativity: The tendency of an atom to attract electrons in a bond.

Examples and Applications

• Example of Ionic Compound: NaCl (table salt) dissolves in water and conducts electricity.

• Example of Covalent Compound: CO2 (carbon dioxide) does not conduct electricity in water.

• Application: Understanding solubility is important in environmental chemistry, medicine, and industrial processes.

Additional info:

• Solubility curves are used to predict how much solute can dissolve at different temperatures.

• Percent by mass is a common way to express concentration in laboratory settings.