Classification and Naming of Compounds: Ionic vs. Molecular

Classification of Chemical Compounds

Bond Types: Covalent vs. Ionic

Chemical compounds are formed by the combination of atoms through chemical bonds. The two primary types of bonds are covalent bonds and ionic bonds.

• Covalent Bonds: Formed when two nonmetal atoms share electrons. The resulting compounds are called molecular compounds.

• Ionic Bonds: Formed when a metal atom transfers electrons to a nonmetal atom, resulting in oppositely charged ions that attract each other. These compounds are called ionic compounds.

Key Properties:

• Ionic Compounds: High melting and boiling points, conduct electricity when dissolved in water, often crystalline solids.

• Molecular Compounds: Lower melting and boiling points, do not conduct electricity in water, may exist as gases, liquids, or solids.

Example: Sodium chloride (NaCl) is an ionic compound; water (H2O) is a molecular compound.

Classification by Formula and Properties

Compounds can be classified based on their chemical formula and observed properties.

• Ionic Compounds: Typically contain a metal and a nonmetal (e.g., NaCl, CaCO3).

• Molecular Compounds: Composed only of nonmetals (e.g., CO2, NH3).

Types of Substances

Atomic Elements, Molecular Elements, Molecular Compounds, Ionic Compounds

Substances can be classified into four main categories:

• Atomic Elements: Exist in nature as single atoms (e.g., noble gases like Ne, Ar).

• Molecular Elements: Exist as molecules composed of two or more atoms of the same element (e.g., O2, N2).

• Molecular Compounds: Composed of molecules formed from different nonmetal elements (e.g., H2O, CO2).

• Ionic Compounds: Composed of positive and negative ions (e.g., NaCl, MgSO4).

Naming Ionic Compounds

Binary Ionic Compounds and Polyatomic Ions

Naming ionic compounds follows specific rules depending on the types of ions involved.

• Binary Ionic Compounds: Consist of a metal and a nonmetal. The metal (cation) is named first, followed by the nonmetal (anion) with its ending changed to -ide. Example: NaCl is named sodium chloride.

• Ionic Compounds with Polyatomic Ions: Contain ions composed of multiple atoms (e.g., SO42−, NO3−). The name of the polyatomic ion is used as is. Example: Na2SO4 is named sodium sulfate.

• Transition Metal Ions: May have multiple possible charges. The charge is indicated by a Roman numeral in parentheses. Example: FeCl2 is iron(II) chloride; FeCl3 is iron(III) chloride.

Writing Formulas for Ionic Compounds

From Name to Formula

To write the formula of an ionic compound from its name:

1. Identify the cation and anion, including their charges.

2. Balance the charges so the total positive and negative charges are equal.

3. Write the formula using the lowest whole number ratio of ions.

Example: Magnesium chloride: Mg2+ and Cl− combine to form MgCl2.

Table: Classification of Substances

Type	Example	Key Features
Atomic Element	Ne	Single atoms
Molecular Element	O2	Two or more atoms of same element
Molecular Compound	CO2	Nonmetals, covalent bonds
Ionic Compound	NaCl	Metal + nonmetal, ionic bonds

Additional info: Polyatomic ions include groups like sulfate (SO42−), nitrate (NO3−), and ammonium (NH4+).

Key Equations

• General formula for ionic compounds: $M^{n+} + X^{m-} ightarrow M_{m}X_{n}$