Properties of Compounds

How the type of chemical bond determines the physical behavior of substances

CAPS Grade 10 Physical Sciences

Properties of compounds are directly determined by the type of chemical bonding present. Understanding these relationships helps predict how substances will behave in different situations.

1. Melting and Boiling Points

Ionic Compounds

HIGH melting & boiling points

High

Strong electrostatic forces between ions in the crystal lattice require significant energy to overcome.

Example: NaCl melts at 801°C, boils at 1465°C

Covalent (Molecular)

LOW melting & boiling points

Low

Weak intermolecular forces between molecules require little energy to overcome.

Example: H₂O boils at 100°C, CH₄ boils at -161°C

Giant Covalent

VERY HIGH melting points

Extremely High

Extensive networks of covalent bonds create a robust framework requiring enormous energy to break.

Examples: Diamond, Graphite, Silica (SiO₂) - all melt above 3500°C

Metallic

HIGH melting points

High

Strong attraction between positive ions and sea of delocalised electrons requires considerable energy to disrupt.

Example: Iron melts at 1538°C, Copper at 1085°C

Rank the Melting Points

Click on the compound with the HIGHEST melting point:

2. Electrical Conductivity

Ionic Compounds

🔋 → Solid

Solid: No conductivity (ions fixed in lattice)

🔋 → Molten/Aqueous

Molten/Aqueous: Conducts (ions free to move)

Covalent Compounds

🔋 → All states

Non-conductors in all states (no free ions/electrons)

Exception: Graphite conducts electricity due to delocalised electrons in its layers.

Metallic Compounds

🔋 → Solid & Liquid

Excellent conductors in both solid and liquid states

Delocalised electrons are free to move throughout the structure.

Conductivity Challenge

Will this substance conduct electricity?

3. Solubility

Ionic Compounds

Soluble in polar solvents (like water)

Water molecules interact with charged ions, pulling them apart.

Example: NaCl dissolves in water

Covalent Compounds

Non-polar: Soluble in non-polar solvents (oil, benzene)

Polar covalent: May dissolve in water (e.g., sugar)

Examples: Oil in petrol (soluble), Sugar in water (soluble), Wax in water (insoluble)

Solubility Quick Check

Which statement is TRUE?

4. Malleability and Brittleness

Ionic Solids

Brittle - shatter when force is applied

When force is applied, like charges align and repel each other, causing the crystal to shatter.

Metals

Malleable (can be hammered into shape) and Ductile (can be drawn into wires)

Metal block

The sea of delocalised electrons allows metal kernels to slide past each other without breaking bonds.

Summary of Properties by Bond Type

Property Ionic Covalent (Molecular) Giant Covalent Metallic
Melting/Boiling Points High Low Very High High
Electrical Conductivity Only when molten/aqueous Poor (except graphite) Poor (except graphite) Excellent
Solubility Soluble in polar solvents Soluble in non-polar solvents Insoluble Insoluble (except in acids)
Malleability Brittle Brittle (molecular crystals) Brittle Malleable & Ductile

Test Your Understanding

1. Why do ionic compounds have high melting points?

2. When do ionic compounds conduct electricity?

3. Which property allows metals to be drawn into wires?

4. Which is an exception to the rule that covalent compounds don't conduct electricity?

Key Terms

Melting point Boiling point Electrical conductivity Solubility Malleable Ductile Brittle Crystal lattice Delocalised electrons Intermolecular forces Electrostatic forces Polar solvent

Key Takeaways

Three Main Types of Bonding Electronegativity