Ionic vs. Covalent Compounds and Solubility: Study Notes

Unit 3: Ionic vs. Covalent Compounds and Solubility

Vocabulary and Key Concepts

This section introduces essential terms and concepts related to ionic and covalent compounds, solubility, and solution chemistry.

• Ionic Compound: A compound consisting of positive and negative ions held together by electrostatic forces. Typically formed between metals and nonmetals.

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

• Solubility: The ability of a substance to dissolve in a solvent.

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

• Solvent: The substance that does the dissolving, usually present in greater amount.

• 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, leading to partial positive and negative ends.

Classifying Matter

Matter can be classified as elements, compounds, or mixtures based on its composition and chemical bonding.

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

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

• Mixture: A combination of two or more substances that are not chemically bonded and can be separated by physical means.

Example: Sodium chloride (NaCl) is a compound because it contains sodium and chlorine chemically bonded in a fixed ratio.

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.

• Covalent Bonds: Formed by the sharing of electrons between 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 solution

  • May be soluble or insoluble in water

Example: NaCl (table salt) is ionic; H2O (water) is covalent.

Identifying Ionic and Covalent Compounds

Compounds can be identified as ionic or covalent based on the types of elements present.

Compound	Metal or Nonmetal	Ionic or Covalent Bond?
SO2	Nonmetal	Covalent
MgBr2	Metal + Nonmetal	Ionic
Pt	Metal	None (element)
H2	Nonmetal	Covalent
CaO	Metal + Nonmetal	Ionic
NaCl	Metal + Nonmetal	Ionic
CO2	Nonmetal	Covalent

Bonding and Electron Transfer

Chemical bonds involve the sharing or transfer of electrons between atoms.

• Covalent Bonds: Involve the sharing of electrons between nonmetals.

• Ionic Bonds: Involve the transfer of electrons from metals to nonmetals.

Equation:

$\text{Na} + \text{Cl} \rightarrow \text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl}$

Solubility and Solutions

Solubility describes how much solute can dissolve in a solvent at a given temperature. Solutions are classified based on their concentration.

• Solute: The substance being dissolved.

• Solvent: The substance doing the dissolving.

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

• Unsaturated Solution: Contains less solute than can be dissolved at a given temperature.

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

Example: Adding more salt to water increases the concentration; removing water also increases concentration.

Concentration and Percent by Mass

Concentration can be expressed as percent by mass, which is the mass of solute divided by the total mass of solution, multiplied by 100.

Equation:

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

• Example Calculation: If 75 g of solute is added to 150 g of water, the percent by mass is:

$\frac{75}{150+75} \times 100 = 33.33\%$

Solubility Graphs

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

• Reading the Graph: Points above the curve indicate supersaturated solutions; points on the curve indicate saturated solutions; points below the curve indicate unsaturated solutions.

• Example: At 20°C, KNO3 is more soluble than KCl.

Parts per Million (ppm)

Concentration of very dilute solutions can be expressed in parts per million (ppm).

Equation:

$\text{ppm} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 1,000,000$

• Example: If 0.013 g of manganese is found in 1000 g of water:

$\frac{0.013}{1000} \times 1,000,000 = 13 \text{ ppm}$

Summary Table: Properties of Ionic vs. Covalent Compounds

Property	Ionic Compounds	Covalent Compounds
Bonding	Transfer of electrons	Sharing of electrons
Elements Involved	Metal + Nonmetal	Nonmetal + Nonmetal
Melting/Boiling Point	High	Low
Electrical Conductivity (in solution)	Conducts	Does not conduct
Solubility in Water	Usually soluble	Varies

Additional info: These notes expand on the original questions and vocabulary by providing definitions, examples, and equations for key concepts in introductory chemistry related to ionic and covalent compounds and solution chemistry.