Ionic vs. Covalent Compounds and Solubility: Study Guide

Unit: Ionic vs. Covalent Compounds and Solubility

Vocabulary and Key Concepts

This section introduces essential terms and definitions related to ionic and covalent compounds, solubility, and classification of matter.

• Ionic Compound: A chemical compound composed of ions held together by electrostatic forces termed ionic bonding. Typically formed between metals and nonmetals.

• Covalent Compound: A compound where atoms share electrons; usually formed between nonmetals.

• Solute: The substance that is dissolved in a solution.

• Solvent: The substance that dissolves the solute, often present in greater amount.

• Solution: A homogeneous mixture of two or more substances.

• High Concentration: A solution with a large amount of solute relative to solvent.

• Low Concentration: A solution with a small amount of solute relative to solvent.

• Metal: An element that is lustrous, conducts electricity, and is malleable.

• Nonmetal: An element that is not lustrous, has a low melting point, and does not conduct electricity well.

Classifying Matter

Matter can be classified based on its composition and properties. Understanding the differences between elements, compounds, and mixtures is fundamental in chemistry.

• Element: A pure substance consisting of only one type of atom.

• Compound: A substance formed when two or more elements are chemically bonded together.

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

Order of Types of Matter (from most to least basic):

• Elements

• Atoms

• Compounds

Comparison: Compounds have a constant composition, while mixtures have variable composition.

Ionic vs. Covalent Compounds

Ionic and covalent compounds differ in their bonding, properties, and the types of elements involved.

• Ionic Bonds: Formed by the transfer of electrons from a metal to a nonmetal, resulting in positive and negative ions that attract each other.

• Covalent Bonds: Formed by the sharing of electrons between two nonmetals.

• Properties of Ionic Compounds:

  • High melting and boiling points

  • Conduct electricity when dissolved in water

  • Usually soluble in water

• Properties of Covalent Compounds:

  • Lower melting and boiling points

  • Do not conduct electricity in water

  • May be soluble or insoluble in water

Example: Sodium chloride (NaCl) is an ionic compound; water (H2O) is a covalent compound.

Identifying Ionic and Covalent Compounds

Compounds can be identified as ionic or covalent based on the elements involved and their properties.

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

Naming Ionic and Covalent Compounds

Compounds are named according to specific rules based on their type.

• Ionic Compounds: Name the metal (cation) first, then the nonmetal (anion) with an -ide ending.

• Covalent Compounds: Use prefixes to indicate the number of atoms (mono-, di-, tri-, etc.) and name the elements in order.

Example: CO2 is carbon dioxide; NaCl is sodium chloride.

Solubility and Solutions

Solubility refers to the ability of a substance (solute) to dissolve in a solvent to form a solution. The concentration of a solution is the amount of solute dissolved in a given amount of solvent.

• Soluble: A substance that can dissolve in a solvent.

• Insoluble: A substance that cannot dissolve in a solvent.

• Saturated Solution: A solution that contains the maximum amount of dissolved solute at a given temperature.

• Unsaturated Solution: A solution that contains less than the maximum amount of solute.

Example: Sugar dissolving in water forms a solution; if more sugar is added than can dissolve, the solution becomes saturated.

Solubility Graphs

Solubility graphs show how the solubility of substances changes with temperature. These graphs are used to determine whether a solution is saturated, unsaturated, or supersaturated at a given temperature.

• To find if a solution is saturated, locate the amount of solute and temperature on the graph; if the point is on the curve, the solution is saturated.

• If the point is below the curve, the solution is unsaturated; above the curve, it is supersaturated.

Example: At 40°C, the solubility of KNO3 is about 65 g per 100 g water. Adding 70 g at this temperature would result in a supersaturated solution.

Calculating Percent Mass of Solute in Solution

The percent by mass of a solute in a solution is calculated using the formula:

• Percent by mass formula:

$\text{Percent by mass} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100$

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

Additional Info

• Electronegativity: Ionic bonds form between elements with large differences in electronegativity; covalent bonds form between elements with similar electronegativity.

• Conductivity: Only ionic compounds conduct electricity in solution due to the presence of ions.