STATES OF MATTER

LEARNING OBJECTIVES

• Identify and describe the three states of matter

• Explain the properties of solids, liquids, and gases

• Understand the arrangement and movement of particles in each state

• Describe the changes of state between different materials

• Define melting point and boiling point

KEY DEFINITIONS

• State of matter: The physical form that a substance can take (solid, liquid, or gas)

• Melting: Change of state from solid to liquid when heated

• Freezing: Change of state from liquid to solid when cooled

• Boiling: Rapid change of state from liquid to gas at a specific temperature

• Condensation: Change of state from gas to liquid when cooled

• Sublimation: Change of state directly from solid to gas without passing through liquid state

• Melting point: The temperature at which a solid changes into a liquid

• Boiling point: The temperature at which a liquid changes into a gas

• Latent heat: The energy required to change the state of a substance without changing its temperature

PROPERTIES OF SOLIDS

• Fixed shape: Solids have a definite shape that does not change

• Fixed volume: Solids have a definite volume that does not change

• Incompressible: Cannot be compressed (particles are tightly packed)

• Particle arrangement: Particles are packed closely together in fixed positions

• Particle movement: Particles vibrate in fixed positions but cannot move around

• Density: Generally high (particles closely packed)

• Examples: Ice, iron, diamond, salt, rock

Why solids have these properties:

• Particles are held tightly in place by strong intermolecular forces

• Particles cannot move past each other

• Only vibration is possible around fixed positions

PROPERTIES OF LIQUIDS

• No fixed shape: Liquids take the shape of their container

• Fixed volume: Liquids have a definite volume that does not change

• Slightly compressible: Can be compressed but not easily

• Particle arrangement: Particles are close together but not in fixed positions

• Particle movement: Particles move around each other randomly

• Density: Generally less than solids, more than gases

• Examples: Water, milk, oil, mercury, alcohol

Why liquids have these properties:

• Particles have enough energy to move past each other

• Intermolecular forces are weaker than in solids

• Particles are still close enough to maintain fixed volume

PROPERTIES OF GASES

• No fixed shape: Gases expand to fill the entire space available

• No fixed volume: Gases can be compressed or expanded easily

• Highly compressible: Can be compressed significantly

• Particle arrangement: Particles are very far apart from each other

• Particle movement: Particles move freely and rapidly in random directions

• Density: Generally very low (particles far apart)

• Examples: Oxygen, nitrogen, carbon dioxide, hydrogen, chlorine

Why gases have these properties:

• Particles have high kinetic energy and move rapidly

• Intermolecular forces are very weak

• Particles collide with container walls causing pressure

COMPARISON OF THREE STATES OF MATTER

CHANGES OF STATE

1. MELTING (Solid → Liquid)

• Definition: Solid changes to liquid when heated

• What happens: Particles gain energy and vibrate more vigorously

• Particles break free from fixed positions and start moving

• Temperature: Occurs at melting point (specific for each substance)

• Example: Ice melts at 0°C to form water

• Energy required: Latent heat of fusion (energy absorbed without temperature change)

2. FREEZING (Liquid → Solid)

• Definition: Liquid changes to solid when cooled

• What happens: Particles lose energy and move more slowly

• Particles return to fixed positions

• Temperature: Occurs at freezing point (same as melting point)

• Example: Water freezes at 0°C to form ice

• Energy released: Latent heat is released

3. BOILING/EVAPORATION (Liquid → Gas)

• Definition: Liquid changes to gas when heated

• What happens: Particles gain enough energy to overcome intermolecular forces

• Particles escape from liquid and form a gas

• Temperature: Occurs at boiling point (specific for each substance)

• Example: Water boils at 100°C to form water vapor (steam)

• Energy required: Latent heat of vaporization (more energy than melting)

4. CONDENSATION (Gas → Liquid)

• Definition: Gas changes to liquid when cooled

• What happens: Particles lose energy and slow down

• Particles come close enough together to form liquid

• Temperature: Occurs at boiling point (same as condensation point)

• Example: Water vapor condenses to form water droplets

• Energy released: Latent heat is released

5. SUBLIMATION (Solid → Gas)

• Definition: Solid changes directly to gas without becoming liquid

• What happens: Particles gain enough energy to escape solid state completely

• Occurs in certain solids only

• Example: Dry ice (solid carbon dioxide) sublimes directly to carbon dioxide gas

• Example: Iodine crystals sublime when heated

• Energy required: Latent heat of sublimation

6. DEPOSITION (Gas → Solid)

• Definition: Gas changes directly to solid without becoming liquid

• What happens: Particles lose energy and come together to form solid directly

• Reverse process of sublimation

• Occurs when gas is cooled sufficiently

• Example: Frost formation - water vapor in air deposits directly as ice crystals on cold surfaces

• Example: Snow formation - water vapor deposits as ice crystals in clouds

• Energy released: Latent heat is released during deposition

MELTING POINT AND BOILING POINT

Melting Point:

• The fixed temperature at which a solid changes to liquid

• Different substances have different melting points

• At melting point, solid and liquid exist together in equilibrium

• Temperature does not change during melting (energy goes into breaking bonds)

• Examples: Ice melts at 0°C, iron melts at 1535°C

Boiling Point:

• The fixed temperature at which a liquid changes to gas

• Different substances have different boiling points

• At boiling point, bubbles of gas form throughout the liquid

• Temperature does not change during boiling (energy goes into breaking bonds)

• Examples: Water boils at 100°C, alcohol boils at 78°C

Key points:

• Melting point and freezing point of a substance are the same temperature

• Boiling point and condensation point of a substance are the same temperature

• Pure substances have fixed, definite melting and boiling points

• Melting point < Boiling point (always)