Ionic vs. Covalent Compounds and Solubility: Study Guide

Unit: Ionic vs. Covalent Compounds and Solubility

Vocabulary and Key Concepts

This section introduces essential terminology and foundational concepts for understanding ionic and covalent compounds, as well as solubility in chemistry.

• 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, forming a solution.

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

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

• Nonmetal: An element that is not lustrous, does not conduct electricity, and is brittle.

• 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.

• Precipitate: A solid that forms and settles out of a liquid mixture.

Classifying Matter

Matter can be classified based on its composition and properties. Understanding these classifications is fundamental to chemistry.

• Elements: Pure substances consisting of only one type of atom.

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

• Compounds: Substances formed when two or more elements are chemically bonded together.

• Mixtures: Physical combinations of two or more substances where each retains its own properties.

Example: Water (H2O) is a compound, while air is a mixture of gases.

Properties of Ionic and Covalent Compounds

Ionic and covalent compounds differ in their composition, bonding, and physical properties.

• Ionic Compounds:

  • Formed from metals and nonmetals.

  • High melting and boiling points.

  • Conduct electricity when dissolved in water (electrolytes).

  • Usually solid at room temperature.

• Covalent Compounds:

  • Formed from nonmetals.

  • Lower melting and boiling points compared to ionic compounds.

  • Do not conduct electricity in water (nonelectrolytes).

  • Can be solid, liquid, or gas at room temperature.

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

Identifying Ionic and Covalent Compounds

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

Compound	Metal or nonmetal	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 each atom (e.g., carbon dioxide, CO2).

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

Bonding in Compounds

The type of bond in a compound determines its properties.

• Ionic Bonds: Formed by the transfer of electrons from a metal to a nonmetal.

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

Example: In NaCl, sodium donates an electron to chlorine, forming Na+ and Cl-.

Solubility and Solutions

Solubility refers to the ability of a substance to dissolve in a solvent. Solutions are classified based on the amount of solute dissolved.

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

• Unsaturated Solution: Can dissolve more solute at the same temperature.

• Supersaturated Solution: Contains more solute than can theoretically dissolve at a given temperature.

Example: Adding sugar to water until no more dissolves creates a saturated solution.

Solubility Graphs

Solubility graphs show how the solubility of substances changes with temperature.

• Solubility generally increases with temperature for most solids.

• For gases, solubility decreases as temperature increases.

Example: At 80°C, more KNO3 can dissolve in water than at 20°C.

Calculating Percent Mass of Solute in Solution

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

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

Example: If 5 grams of NaCl are dissolved in 95 grams of water, the percent by mass is:

$\frac{5}{5+95} \times 100 = 5\%$

Conductivity and Dissociation

Ionic compounds conduct electricity when dissolved in water because they dissociate into ions. Covalent compounds generally do not conduct electricity in solution.

• Electrolyte: A substance that produces ions in solution and conducts electricity.

• Nonelectrolyte: A substance that does not produce ions in solution.

Example: NaCl is an electrolyte; sugar is a nonelectrolyte.

Summary Table: Properties of 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 solution)	Conducts	Does not conduct
Physical State (room temp)	Solid	Solid, liquid, or gas

Additional info:

• To increase the concentration of a solution, add more solute or evaporate some solvent.

• When a precipitate forms, it indicates the solution is saturated or a chemical reaction has occurred.

• Safe drinking water standards often specify maximum allowable concentrations for certain ions or elements (e.g., manganese in ppm).