Structure & Properties of Simple Molecules
Chemistry: Cambridge International GCSE Supplement, topic 2.5.3
Structure & Properties of Simple Molecules
Simple molecular compounds have strong covalent bonds within molecules but weak intermolecular forces between them, leading to low melting/boiling points and poor electrical conductivity.
Structure of simple molecular compounds
- Simple molecular compounds have small groups of atoms called molecules.
- Atoms in molecules connect by covalent bonds.
- Covalent bonds form when atoms share electrons.
- Molecules become weakly attracted by forces called intermolecular forces.
- Intermolecular forces are much weaker than covalent bonds.
Low melting and boiling points
- Simple molecular compounds have low melting and boiling points.
- Intermolecular forces take little energy to break.
- Covalent bonds inside molecules remain intact during melting or boiling.
- Examples: Water (H2O) melts at 0°C, boils at 100°C; iodine (I2) melts at 114°C.
- Weak forces explain why simple molecules are often gases or liquids at room temperature.
Poor electrical conductivity
- Simple molecular compounds do not conduct electricity well.
- Molecules have no free charged particles to carry an electric current.
- Covalent bonds keep electrons fixed between atoms.
- When dissolved in water, some molecular compounds cannot form ions.
- Hence, they act as insulators in both solid and liquid states.
Summary of properties and structure
- Simple molecular compounds have molecules held by covalent bonds.
- Weak intermolecular forces cause low melting and boiling points.
- Lack of free charged particles leads to poor electrical conductivity.
Test yourself on Structure & Properties of Simple Molecules
How do atoms form covalent bonds?