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 the classification of matter.

• Ionic Compound: A compound consisting of positively and negatively charged ions held together by electrostatic forces. 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; in aqueous solutions, water is the solvent.

• 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 chemistry.

• Elements: Pure substances consisting of only one type of atom (e.g., O2, Fe).

• Compounds: Substances composed of two or more elements chemically combined in fixed ratios (e.g., H2O, NaCl).

• Mixtures: Physical combinations of two or more substances that retain their individual properties (e.g., air, saltwater).

Order of Classification (from most to least pure): Elements → Compounds → Mixtures

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

Compounds vs. Mixtures: Compounds have fixed compositions and properties, while mixtures can vary in composition and can be separated by physical means.

Ionic and Covalent Compounds: Identification and Properties

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

• Ionic Compounds:

  • Formed between metals and nonmetals.

  • Consist of ions held together by electrostatic attraction.

  • High melting and boiling points.

  • Conduct electricity when dissolved in water (electrolytes).

  • Example: NaCl (sodium chloride)

• Covalent Compounds:

  • Formed between nonmetals.

  • Atoms share electrons to achieve stability.

  • Lower melting and boiling points compared to ionic compounds.

  • Do not conduct electricity in water.

  • Example: H2O (water)

Identifying Ionic vs. Covalent Bonds: In a compound, the metal is always listed first. If the compound contains a metal and a nonmetal, it is ionic; if it contains only nonmetals, it is covalent.

Table: Identifying Ionic and Covalent Compounds

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

• Ionic Compounds: Name the metal (cation) first, then the nonmetal (anion) with an -ide ending. For polyatomic ions, use the ion's name (e.g., sodium sulfate).

• Covalent Compounds: Use prefixes to indicate the number of each atom (e.g., carbon dioxide, dinitrogen monoxide).

Properties Comparison: Ionic vs. Covalent Compounds

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

Solubility and Solutions

Solubility refers to the ability of a substance (solute) to dissolve in a solvent to form a homogeneous solution.

• 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; unstable.

• Solubility Curve: A graph showing how solubility changes with temperature for various substances.

Solubility Curve Interpretation

• To determine if a solution is saturated, unsaturated, or supersaturated, locate the amount of solute and temperature on the curve.

• Points on the curve represent saturation; below the curve is unsaturated, above is supersaturated.

Calculating Percent Mass of Solute in Solution

The percent by mass of a solute in a solution is calculated as:

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

Example: If 5 grams of MgCl2 are dissolved in 95 grams of water, the percent by mass is:

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

Concentration Units

• ppm (parts per million): Used for very dilute solutions. Calculated as:

$\text{ppm} = \frac{\text{mass of solute (mg)}}{\text{mass of solution (kg)}}$

Example: If 0.013 grams of manganese are found in 1000 grams of water:

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

Summary Table: Key Differences Between Ionic and Covalent Compounds

Characteristic	Ionic Compounds	Covalent Compounds
Type of Elements	Metal + Nonmetal	Nonmetal + Nonmetal
Bond Type	Electrostatic attraction	Electron sharing
Electrical Conductivity	Yes (in solution)	No
Melting Point	High	Low to moderate

Additional info:

• When describing solubility, temperature often increases the solubility of solids in liquids but can decrease the solubility of gases.

• Electrolytes are substances that conduct electricity when dissolved in water; all ionic compounds are electrolytes.