iGCSE Chemistry (Combined) CAIE

The Particulate Nature of Matter

The Particulate Nature of Matter

Basic Principles

• All substances are made of particles.
• These particles could be atoms, molecules, or ions.
• These particles are in constant motion; higher the temperature, quicker the movement.
• There are spaces between particles.

States of Matter

• Matter exists in three states: Solid, Liquid, and Gas.
• In solids, particles are packed closely in a fixed pattern. They can only vibrate around a fixed point.
• In liquids, particles are close but can move around each other. This means liquids can flow and take shape of their containers.
• In gases, particles are well separated and move quickly in all directions. Gases fill their containers completely.

Changes of States

• Melting and Freezing: The change from solid to liquid is called melting, whereas the change from liquid to solid is freezing.
• Boiling and Condensing: Liquid turning into gas is boiling or evaporation, while gas changing to liquid is called condensing.
• Sublimation: Certain substances can change from solid directly to gas, bypassing the liquid state. This process is called sublimation.

Kinetic Particle Theory

• The Kinetic Particle Theory explains the properties of different states of matter.
• This theory considers both the movement of particles (kinetic energy) and the attraction between them.
• In solids, the attractive forces are strong, keeping particles in fixed positions, so solids keep their shape.
• In liquids, the attractive forces are weaker, allowing particles to move and slide past each other.
• In gases, the attractive forces are very weak, letting particles move rapidly in all directions.

Diffusion

• Diffusion is the spreading of particles from an area of high concentration to one of low concentration.
• Diffusion occurs most quickly in gases, slower in liquids, and slowest in solids.
• Increased temperature boosts the speed of diffusion by increasing particle motion.

Brownian Motion

• Brownian Motion is the random, unpredictable movement of particles in a fluid, as observed under a microscope.
• This motion is caused by the collisions of the particles with each other.
• Brownian Motion is additional evidence of the particle nature of matter.