Contents are appropriate for IGCSE Physics

1. SIMPLE KINETIC MOLECULAR MODEL OF
MATTER

2. What is matter?
 Matter is anything that occupies space and has mass.
 Matter is made up of tiny particles called atoms.
 The tiny particles that make up matter are in constant
motion.
 There are 3 states of matter:
 Solid
 Liquid
 Gas

3. 1. SOLID
 A solid is any material that has a fixed shape and fixed
volume.
 Its particles are held by strong forces of attraction
called bonds.
 The particles vibrate to and fro about their fixed
positions.
 Examples include:
 Iron
 Concrete
 Wood
 Glass etc.

4. 2. LIQUID
 A liquid has a fixed volume but no fixed shape.
 It can flow to fill up any shape.
 It is also called a fluid.
 The particles are loosely packed.
 They vibrate vigorously that the attractions cannot
hold them in fixed positions.
 They can move past each other (sliding).
 Examples include:
 Water
 Hydrochloric acid
 Chlorine etc.

5. 3. GAS
 A gas is a material that has no fixed shape and no fixed volume.
 A gas quickly fills up any space available.
 A gas is also a fluid because it can move from one point to
another.
 The particles are spaced packed.
 Particles of a gas are free to move about.
 There are no forces of attraction.
 Particles move at high speeds
 They collide with one another and the walls of the container.
 Examples include:
 Oxygen
 Carbon dioxide
 Ammonia
 Hydrogen etc.

8. ENERGY OF PARTICLES
 Particles in a solid and liquid are attracted to each
other by forces of attraction. These forces provide
potential energy for the particles.
 Particles of matter are in constant motion. They have
kinetic energy.
 Gases have the highest total energy because their
particles are far apart and are moving at high speeds
Potential
energy
Kinetic
energy
Total energy
Solid Lowest Lowest Lowes
Liquid Medium Medium Medium
Gas Highest Highest Highest

9. THERMAL ENERGY
 The total energy (potential + kinetic) of all the atoms
in a material is called internal energy.
 The hotter the material, the faster the particles move.
 Energy can be transferred from one object to another
e.g. a hotter object loses heat to a colder one. This form
of energy transfer is called heat.
 Both internal energy and heat are called thermal
energy.

10. TEMPERATURE
 An object whose particles move faster has more
thermal energy.
 The faster the particles, the higher the kinetic energy,
the greater the thermal energy and the hotter the
object.
 Temperature is related to kinetic energy of particles.
 Temperature is the average kinetic energy of
particles in an object.

11. EVAPORATION
 Evaporation is a process by which a liquid changes into
gas.
 It happens because some particles move faster than
others.
 Evaporation takes place on the surface of the liquid.
 Evaporation brings cooling.
 Molecules or particles that have the most energy
escape from the liquid.
 Molecules or particles with the most energy break free
from the attractive forces.

12. FACTORS AFFECTING THE RATE OF
EVAPORATION
1. TEMPERATURE
- The higher the temperature, the faster the rate of evaporation
because particles gain more energy at a faster rate.
2. SURFACE AREA
- A larger surface area exposes more particles. The rate of
evaporation is faster with a larger surface area.
3. HUMIDITY
-Humidity is the amount of moisture in the atmosphere. A higher
humidity means there is more moisture in the atmosphere and
thus a slower rate of evaporation. Low humidity gives a higher
rate of evaporation.
4. WIND SPEED
- Blowing air carries particles on the surface of the liquid.
- When wind speed is high, the rate of evaporation is high.