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 formed when two or more nonmetal atoms share electrons.

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

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

• 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.

• Polar Molecule: A molecule with an uneven distribution of charge, resulting in positive and negative ends.

Classifying Matter

Matter can be classified based on its composition and properties. Understanding these classifications is fundamental to distinguishing between elements, compounds, and mixtures.

• 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 common): Elements, compounds, mixtures.

Atoms vs. Elements: An atom is the smallest unit of an element that retains its chemical properties. An element is a substance made entirely of one type of atom.

Metals in Compounds: In chemical formulas, the metal is always listed first in an ionic compound.

Ionic vs. Covalent Compounds: Identification and Properties

Ionic and covalent compounds differ in their composition, bonding, and properties. The following table helps identify the type of bond based on the elements involved.

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

Additional info: Table entries inferred based on standard chemical knowledge.

Naming Ionic and Covalent Compounds

Correctly naming compounds is essential for clear communication in chemistry.

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

• Covalent Compounds: Use prefixes (mono-, di-, tri-, etc.) to indicate the number of each atom.

Examples:

• CaCl2: Calcium chloride (ionic)

• CO2: Carbon dioxide (covalent)

• NaBr: Sodium bromide (ionic)

• SO2: Sulfur dioxide (covalent)

Properties of Ionic and Covalent Compounds

Ionic and covalent compounds exhibit distinct physical and chemical properties.

• Ionic Compounds:

  • High melting and boiling points

  • Conduct electricity when dissolved in water (electrolytes)

  • Usually soluble in water

  • Formed from metals and nonmetals

• Covalent Compounds:

  • Lower melting and boiling points compared to ionic compounds

  • Do not conduct electricity in water

  • Often insoluble or less soluble in water

  • Formed from nonmetals only

Solubility and Solutions

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

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

• Unsaturated Solution: Contains less solute than the maximum amount that can dissolve.

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

Solubility Graphs: Used to determine how much solute can dissolve in a solvent at various temperatures.

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 MgCl2 are dissolved in 95 grams of water, the percent by mass is:

$\text{Percent by mass} = \frac{5}{5 + 95} \times 100 = 5\%$

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.

• Dissociation: The process by which an ionic compound separates into ions when dissolved in water.

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

Summary Table: Comparison of Ionic and Covalent Compounds

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

Application: Solubility and Concentration Calculations

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

• To decrease the concentration, add more solvent or remove some solute.

• Solubility graphs can be used to determine the amount of solute that will dissolve at a specific temperature.

Example Calculation: If 0.013 grams of manganese are found in 1000 grams of water, the concentration in ppm (parts per million) is:

$\text{ppm} = \frac{0.013}{1000} \times 10^6 = 13\ ppm$

Additional info: Safe drinking water standards typically require manganese concentrations below 50 ppm.