Project Overview

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Discover Physics for GCE O Level Science
Unit 7 Kinetic Model of Matter
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7.1 The States of Matter

• Learning Outcomes
• In this section, youll be able to
• Compare the properties of solids, liquids and
  gases
• Describe the molecular structure of solids,
  liquids and gases
• Describe Brownian motion
• Describe the effects of temperature on Brownian
  motion

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7.1 The States of Matter

• Matter exists as a solid, liquid and gas.
• These are referred to as the three states of
  matter.
• Similarly, substances can exist in three states.
• The properties of a substance differ between each
  states.

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7.1 The States of Matter
Table 7.1 Properties of solids, liquids and gases.
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7.1 The States of Matter

• The Kinetic Model of Matter
• All matters are made up of tiny particles called
  atoms or molecules (group of atoms joined
  together)
• These particles are in constant motion.
• The continuous motion of these particles is known
  as kinetic model of matter.
• This theory can explain the difference in
  properties between each states.

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7.1 The States of Matter
Table 7.2 Properties of solids, liquids and gases
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7.1 The States of Matter

• The kinetic model of matter
• The relative strengths of the intermolecular
  forces between the particles differ between the
  different states of matter.
• The relative distances between the particles also
  differ between the different states of matter.

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7.1 The States of Matter

• Evidence of molecular motion (Experiment 7.1)

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7.1 The States of Matter

• Evidence of molecular motion
• From Experiment 7.1 in the textbook, we see that
  smoke particles in air move in a random and
  irregular way.
• This is referred to as Brownian motion.
• Brownian motion occurs only in fluids where the
  particles have the ability to flow or move
  freely.
• Fluids include liquids and gases.

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7.1 The States of Matter

• Effects of temperature on molecular motion
• At higher temperatures, the motion of smoke
  particles will become more vigorous and agitated.
• This is because the air molecules are bombarding
  the smoke particles more vigorously and
  frequently.
• The air molecules have greater speeds at higher
  temperatures.
• The thermal energy is converted to kinetic energy
  of air molecules, causing it to move faster.

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7.1 The States of Matter

• Key Ideas
• 1. All substances exist in three states of
  matter solid, liquid and gas.
• The kinetic model of matter describes matter as
  being made up of tiny particles (atoms or
  molecules) in continuous motion.
• Brownian motion is the random or irregular motion
  of smoke particles in air or pollen grains in
  water. When temperature increases, the smoke
  particles or pollen grains are observed to move
  faster and more vigorously.
• Brownian motion is caused by the bombardment of
  air molecules of smoke particles in air or water
  molecules on pollen grains in water.

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7.1 The States of Matter

• Test Yourself
• 1. Using the kinetic model of matter, explain why
  the density of a gas is much lower than that of a
  solid.
• Answer
• In solids, the particles (or atoms) are closely
  packed.
• In gases, the particles are far apart.
• Since density is the mass per unit volume, then
  solids must have a much higher density since
  there are many more particles packed closely
  together per unit volume compared to gases.

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7.1 The States of Matter

• Test Yourself
• 2. What is Brownian motion in air? What causes
  it?
• Answer
• Brownian motion refers to the random, irregular
  and jerky motion of smoke particles in air.
• The smoke particles are continually bombarded
  unevenly on different sides by
• air molecules. This results in the irregular
  movement of the smoke particles.

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7.1 The States of Matter

• Test Yourself
• 3. (a) As temperature is increased, how would
  the movement of smoke particles in Brownian
  motion change?
• 3. (b) What would you expect to see if the
  smoke particles are much larger?
• Answer
• 3. (a) As temperature increased, the motion of
  the smoke particles become more vigorous and
  agitated.
• 3. (b) Larger smoke particles tend to have less
  irregular and less jerky motion.

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