Ionic Bonding and Properties of Compounds

Ionic Bonding

Dissolve the substance in water and test conductivity with a circuit and bulb. If it only conducts when molten or in solution, not when solid, it contains ionic bonds. Melting point tests can also indicate ionic bonding if the substance has a very high melting point, suggesting strong electrostatic forces.

Compound

A compound is a substance made of two or more different elements chemically bonded together in a fixed ratio. It has different properties from the elements it's made from.

Mixture

A mixture contains substances not chemically bonded and can be separated physically (e.g., filtration, distillation).

Naming Ionic Compounds

For ionic compounds, the metal is named first, followed by the non-metal with an '-ide' ending. If a polyatomic ion is involved, use its name (e.g., sulfate, carbonate).

Chemical Formula of Ionic Compounds

Balance charges to write the correct formula: e.g., Mg²⁺ and Cl⁻ → MgCl₂; e.g., Al³⁺ and SO₄²⁻ → Al₂(SO₄)₃.

Properties of Ionic Compounds

Ionic compounds have high melting points, are soluble in water, conduct when molten/aqueous, and form crystals.

Properties of Covalent Compounds

Covalent (simple molecules) have low melting/boiling points, don't conduct electricity, and are often gases or liquids at room temperature.

Giant Covalent Compounds

Giant covalent compounds have very high melting points, are hard, and sometimes conduct (e.g., graphite).

Simple Molecular Substances

Simple molecules are small, discrete molecules with strong covalent bonds within each molecule and weak intermolecular forces between them.

Examples of Simple Molecular Substances

Examples include Water (H₂O), Carbon dioxide (CO₂), and Methane (CH₄).

Low Melting and Boiling Points of Simple Molecular Substances

Although covalent bonds inside molecules are strong, the intermolecular forces between molecules are weak and require little energy to overcome.

Electrical Conductivity of Simple Molecular Substances

They don't contain ions or free electrons, so they can't carry charge.

Ionic bonding

Ionic bonding is the electrostatic attraction between oppositely charged ions. It forms when a metal loses electrons (forms a cation) and a non-metal gains electrons (forms an anion).

Giant ionic lattice

A regular 3D arrangement of alternating positive and negative ions. Properties: high melting/boiling points, conduct electricity when molten or dissolved, brittle when struck.

Testing ionic bonding

Check if it conducts electricity when molten or in solution (but not as a solid), and has a high melting point — both are signs of ionic bonding.

Compound

A compound is made of two or more elements chemically bonded. It has fixed ratios and different properties from its elements. Mixtures are not chemically bonded and can be separated physically.

Naming ionic compounds

Metal name first, non-metal ends in "-ide". Balance charges in formulas: e.g. Mg²⁺ and Cl⁻ → MgCl₂; Al³⁺ and SO₄²⁻ → Al₂(SO₄)₃.

Properties of ionic compounds

Ionic: high mp/bp, conductive in solution. Simple covalent: low mp/bp, don't conduct. Giant covalent: very high mp/bp, may conduct (e.g. graphite).

Simple molecular substances

Small molecules with strong covalent bonds and weak intermolecular forces. Examples: H₂O, CO₂, CH₄.

Melting/boiling points of simple molecules

Because only weak intermolecular forces need to be overcome — little energy is required to separate the molecules.

Conductivity of simple molecular substances

They don't have free electrons or ions, so they cannot carry electric current.