Ionic vs Covalent Compounds – Detailed Study Notes
Ionic and Covalent Compounds – Detailed Notes
Introduction
Sugar and salt side by side without labels can look similar (white crystalline solids), but they are very different substances.
Tasting to identify substances is not reliable for many compounds and can be toxic, so it is not a valid identification method.
Compounds are formed by chemical combinations of two or more elements.
What is a compound?
Definition: A compound is formed when two or more elements chemically combine.
Two common types by bonding: ionic compounds and covalent compounds.
How to distinguish ionic vs covalent compounds
Ionic compounds: formed from a metal and a nonmetal.
Covalent compounds: formed from two nonmetals or a metalloid and a nonmetal.
Visual/periodic table cue: elements are categorized as metals, nonmetals, or metalloids based on their location.
Metals are colored pink in the given diagram, mostly on the left side of the periodic table.
Nonmetals are colored blue on the right side.
Metalloids (semi-metals) are colored green and lie along a stair‑like pattern between metals and nonmetals.
Hydrogen is an exception, located with the nonmetals on the right.
Ionic compounds
Bond type: ionic bonds are electrostatic forces of attraction between cations (positively charged) and anions (negatively charged).
Classic example: Sodium chloride (table salt).
Na (a metal) and Cl (a nonmetal) form NaCl.
Electron transfer: Na → Na⁺ + e⁻ and Cl + e⁻ → Cl⁻, resulting in an ionic bond.
ext{Na}
ightarrow ext{Na}^+ + e^-
ext{Cl} + e^-
ightarrow ext{Cl}^-
ext{Na} + ext{Cl}
ightarrow ext{Na}^+ + ext{Cl}^-Other common ionic compounds and uses:
Sodium bicarbonate (baking soda): ext{NaHCO}_3 — used in baking, as an antacid, for indigestion relief.
Sodium hydroxide (NaOH): used as a cleaning agent; component of soaps and detergents.
Physical properties of ionic compounds:
Ionic bonds form a crystal lattice; ions arranged in a regular geometric structure.
Very high melting and boiling points due to strong electrostatic forces.
Hard and brittle crystals.
Ceramics (made of ionic compounds) are heat-resistant materials.
Electrical conductivity:
In solid form, ionic compounds are insulators (do not conduct) because ions are fixed in the lattice.
In molten (liquid) or aqueous form, ions are free to move and conduct electricity; these substances are electrolytes.
When an ionic compound dissolves, cations move toward the negative electrode (cathode) and anions move toward the positive electrode (anode).
Solid ionic compounds do not conduct electricity; molten or aqueous forms conduct.
Covalent compounds
Bond type: covalent bonds involve sharing valence electrons between atoms.
Formation and structure:
Atoms are held together in molecules by covalent bonds.
A molecule is the smallest unit of a covalent compound that retains its properties.
Examples:
Table sugar (sucrose): ext{C}{12} ext{H}{22} ext{O}_{11} — covalent molecular compound composed of carbon, hydrogen, and oxygen.
Water: ext{H}_2 ext{O} — covalent bond between hydrogen and oxygen.
Properties of covalent compounds:
Bond strength is high, but intermolecular forces (the attraction between molecules) are relatively weak.
Result: low melting points and boiling points compared to ionic compounds.
Often form gases, liquids, or soft solids at room temperature.
Generally more flammable than ionic compounds; combustion commonly produces ext{CO}2 and ext{H}2 ext{O}.
Conductivity in water:
Covalent compounds typically do not conduct electricity when dissolved in water because they dissociate into molecules rather than ions.
Polarity of covalent bonds:
Covalent bonds can be polar or nonpolar.
Polarity arises from differences in electronegativity between bonded atoms.
Electronegativity difference (Δχ) determines bonding character:
If Δχ is large, electrons are pulled toward one atom, creating partial charges (polar covalent) or complete transfer (ionic) if Δχ ≥ 2.0.
Example: Hydrogen fluoride (HF) has unequal sharing due to electronegativity values: Fluorine (χ ≈ 4.0) and Hydrogen (χ ≈ 2.1).
Δχ = |4.0 − 2.1| = 1.9 < 2.0 → polar covalent bond (not ionic).
Example with identical atoms (e.g., F–F): equal sharing → nonpolar covalent bond.
Summary context:
Polar covalent bonds produce dipoles within molecules (partial positive/negative charges).
Nonpolar covalent bonds occur when electrons are shared equally (often between identical atoms).
Key contrasts: ionic vs covalent compounds
Bonding nature:
Ionic: complete electron transfer from metal to nonmetal; electrostatic attraction between ions.
Covalent: sharing of electrons between nonmetals/metalloids.
Structure:
Ionic: crystalline lattice with strong lattice energy; ions arranged in a regular pattern.
Covalent: discrete molecules; sometimes crystalline in some covalent networks, but generally molecular substances with defined molecules.
Melting/boiling points:
Ionic: high mp/bp due to strong ionic interactions.
Covalent: lower mp/bp due to weaker intermolecular forces.
Hardness and brittleness:
Ionic: hard and brittle due to rigid crystal lattice.
Covalent: often softer and more flexible.
Conductivity:
Ionic: conducts electricity when molten or dissolved in water (electrolytes); insulator in solid form.
Covalent: typically does not conduct electricity, whether solid or dissolved, because there are no freely moving ions.
Bond formation:
Ionic bonds form crystals; covalent bonds can be polar or nonpolar based on electronegativity differences.
Practical implications:
Ionic compounds are common in salts and ceramics; useful for high-temperature applications due to stability.
Covalent compounds include many organic molecules and many gases, liquids, or soft solids with varied reactivity and flammability.
Real-world relevance and connections
Understanding the difference helps explain why table salt and sugar behave differently in cooking, cleaning, and biological systems.
In biology and environmental science, carbon dioxide (CO₂) plays roles in photosynthesis and respiration; excessive CO₂ contributes to global warming.
Water (H₂O) is essential for life, existing in three states and supporting cellular and ecological processes; it also acts as a solvent influencing chemical reactions.
The concept of electrolytes explains how dissolved salts can conduct electricity, enabling electrical processes in chemistry and industry.
Summary quick reference
Ionic compounds
Form: metal + nonmetal
Bond: ionic (electrostatic) between cations and anions
Structure: crystal lattice; hard, brittle
mp/bp: very high
Conductivity: conducts when molten or aqueous; solid form is an insulator
Examples: NaCl, NaHCO₃, NaOH; salts dissolve to form electrolytes
Covalent compounds
Form: nonmetal + nonmetal or metalloid + nonmetal
Bond: covalent (shared electrons); can be polar or nonpolar
Structure: molecules; can be gases, liquids, or solids
mp/bp: generally low
Conductivity: usually does not conduct electricity in water
Examples: H₂O, CO₂, C₁₂H₂₂O₁₁ (sucrose); many organic compounds
Next video note
Topic: Formation of ions
Stay tuned for how ions form and related concepts