Ionic and Covalent Compounds

Ionic Compounds Formation

  • Definition: Ionic compounds form when cations (+) and anions (-) interact.

  • Stabilization: They are held together by ionic bonds.

  • Composition: The simplest ionic compounds are binary, which means they consist of two elements—typically a metal and a nonmetal.

Predicting Formulas for Ionic Compounds

  • Understanding Charges:

    • To predict the formula of an ionic compound, one must first determine the expected charge on each ion.

    • Example:

    • Lithium ion: Li+

    • Sulfur ion: S2-

    • Combining Atoms:

    • Combine atoms in such a way that the overall compound is neutral.

    • Two lithium ions (Li+) combine with one sulfur ion (S2-) to form a neutral compound:

      • Formula: Li2S

      • Charge balance equation: $(2)(+1) + (1)(-2) = 0$

Predicting Formulas with Polyatomic Ions

  • Polyatomic Ions: These ions behave as single units within compounds.

  • Examples of Compounds:

    • Sodium and sulfate ions:

    • Sodium ion: Na+

    • Sulfate ion: SO42-

    • Formula: Na2SO4

    • Magnesium and hydroxide ions:

    • Magnesium ion: Mg2+

    • Hydroxide ion: OH-

    • Formula: Mg(OH)2

Formula Quiz: Iron(III) and Oxide Ions

  • Question: What is the formula of the ionic compound formed between iron(III) ions and oxide ions?

    • a. IO3

    • b. Fe3O2

    • c. Fe2O3

    • d. FeO

Naming Ionic Compounds

  • Cation and Anion:

    • The name of the cation (metal) is always given before the anion (nonmetal).

    • The cation name remains unchanged (e.g., sodium, magnesium).

    • The anion's name changes to end with “-ide” (e.g., chloride, sulfide, oxide).

  • Naming Transition Metals:

    • When naming ionic compounds that involve transition metals, it is necessary to include Roman numerals to indicate the charge of the metal.

    • Example: In FeCl3, the name is written as iron (III) chloride because the iron has a charge of +3.

  • Polyatomic Ions: The name of a polyatomic ion remains unchanged when it forms a compound.

    • Example: For NaOH, it is named sodium hydroxide.

Common Ionic Compounds and Their Uses

  • Table of Ionic Compounds:

    • Ammonium carbonate: (NH4)2CO3

    • Barium sulfate: BaSO4

    • Calcium carbonate: CaCO3

  • Uses:

    • Smelling salts: Ammonium carbonate

    • Compound used to assist in viewing internal organs in X-ray studies: Barium sulfate

    • Antacid: Calcium sulfate

    • Plaster casts: Calcium sulfate

    • Treatment for bipolar disorder: Lithium carbonate (Li2CO3)

    • Laxative: Magnesium hydroxide (Mg(OH)2)

    • Prevention of eye infections in newborns: Silver nitrate (AgNO3)

    • Baking soda: Sodium bicarbonate (NaHCO3)

    • Drain cleaner: Sodium hydroxide (NaOH)

    • Source of iodide ion for the thyroid: Sodium iodide (NaI)

    • Food preservative: Sodium nitrate (NaNO3) and Sodium nitrite (NaNO2)

    • Meat preservative: Sodium acetate (CH3CO2Na)

    • Foot and hand warmers: Compounds with organic or biochemical sources often list the anion before the cation.

Naming Ionic Compounds Example Quiz

  • Question: What is the name for the ionic compound with the formula Al2O3?

    • a. Aluminum(III) oxide

    • b. Aluminum oxide

    • c. Aluminum oxide ion

    • d. Aluminum(II) oxide

Covalent Bonds

  • Definition: Covalent bonds are formed when a pair of valence electrons are shared between two atoms.

  • This contrasts with ionic bonds where electrons are transferred from one atom to another.

Formation of Covalent Bonds

  • Electron Behavior: Elements can gain or lose electrons to become ions, but they can also share electrons.

  • Bonding and Octet Rule: Generally, the number of covalent bonds a nonmetal atom forms is equivalent to the number of electrons needed to reach an octet (8 valence electrons):

    • Examples:

    • Fluorine (F): Has 7 valence electrons; forms 1 bond.

    • Nitrogen (N): Has 5 valence electrons; forms 3 bonds.

    • Carbon (C): Has 4 valence electrons; forms 4 bonds.