The Particulate Nature Of Matter

States of Matter :

Matter refers to a substance that has mass and occupies space. It exists in three states

Properties of solid, liquids and gas:

- Solids: Have a definite shape and volume; their particles are closely packed in a fixed arrangement, vibrating only slightly in place. It cannot be compressed

- Liquids: Have a definite volume but take the shape of their container; their particles are close together but can move past one another. It cannot be compressed

- Gases: Have neither a definite shape nor volume; their particles are far apart and move freely, filling the entire space available. Can be compressed easily

M : Model of representation
A : Arrangement of particles
D : Distance between particles
A : Forces of Attraction between particles
M : Movement of particles
E : Kinetic energy of particles

Solid
- Arrangement of particles → Closely packed in an orderly manner
- Distance between the particles → Particles are close to one another with very little space between them
- Forces of Attraction between particles → Very strong
- Movement of particles → Vibrate about fixed positions
- Kinetic Energy of Particles → Low

- Why does a solid have a fixed shape? → The particles of a solid are held together by very strong forces of attraction ; vibrate about fixed positions and cannot move freely

- Why does a solid have a fixed volume? → A solid cannot be compressed as its particles are already very close to one another

Liquid
- Arrangement of particles → Closely packed in a disorderly, random manner. Slightly further apart than those of a solid
- Distance between the particles → Particles are close to one another with little space between them
- Forces of Attraction between particles → Strong but weaker than in solid
- Movement of particles → Sliding over one another
- Kinetic Energy of Particles → More kinetic energy than in a solid

- Why does a liquid not have a fixed shape? → The particles of a liquid are arranged in a disorderly manner ; have weaker forces of attraction ; are not held in fixed positions and can move freely throughout liquid

- Why does a liquid have a fixed volume? → The particles of a liquid are still packed quite closely together

Gas
- Arrangement of particles → very far apart
- Distance between the particles → Particles are far apart from one another with much space between them
- Forces of Attraction between particles → Very weak
- Movement of particles → Randomly at high speeds in all directions
- Kinetic Energy of Particles → A lot of kinetic energy

- Why does a Gas not have a fixed shape? → The particles of a gas are spread far apart from each other ; have the weakest force of attraction ; have a lot of kinetic energy and are not held in fixed positions

- Why does a gas have a fixed volume? → The particles in gas are far apart from one another. There is space for the particles to be compressed

Changes in state of matter
- Melting : solid → liquid (at melting point)
- Freezing : liquid → solid (at freezing point)
- Boiling : liquid → gas (at boiling point)
- Evaporation : liquid → gas (at any temperature)
- Condensation : gas → liquid
- Sublimation : solid → gas
- Deposition : gas → solid
→ Change in states are reversible

Melting
- melting is the process by which a substance changes from a solid to liquid
- the temperature which a solid melts is its melting point
- When a solid is heated : → Particles gain kinetic energy and vibrate faster
→ Particles over come attractive forces between them and break away from fixed positions
→ Particles now slide over one another. Solid has melted to liquid

How to explain Temperature changes ( Heating curve) :

→ As the solid is heated, particles in the solid gain K.E. , the temperature of the solid increases until it reaches point B, its melting point. At point B, the solid begins to melt
→ Melting occurs at fixed temperature. Energy from heating is used to overcome forces of attraction between the particles. A mixture of solid and liquid exists. Particles do not gain K.E.
→ At point C, the solid has melted. Temperature of the liquid rises as heating continues. Liquid particles gain K.E.

Freezing
- freezing is the change from a liquid to a solid
- the temperature which a liquid freezes is its freezing point
- When a liquid is cooled : → Particles lose kinetic energy and move more slowly
→ Some particles start to settle into fixed positions
→ All the particles settle into fixed positions. Liquid has frozen into a solid

How to explain Temperature changes ( Cooling curve) :

→ Particles in the liquid lose K.E. The temperatures of the liquid drops to freezing point, Q. At Q, the liquid starts to freeze
→ at Q-R, Liquid freezes. A mixture of solid and liquid exists, Temperature remains constant even though cooling continues.
→ During freezing, energy is released as the particles are drawn closer together. Then released energy compensates the energy lost during cooling
→ At R-S, Particles in the solid lose K.E. At R, all the liquid has frozen. The temperature of the solid drops with further cooling

Boiling
- boiling is the change from a liquid to gas at the boiling temperature
- the temperature which a liquid boils is the boiling point
- When a liquid is cooled : → Particles lose kinetic energy and move more slowly
→ Some particles start to settle into fixed positions
→ All the particles settle into fixed positions. Liquid has frozen into a solid

How to explain Temperature changes ( Heating curve) :

→ Particles in the liquid gain K.E. The temperatures of the liquid increases until its boiling point, X, is reached
→ At X-Y, liquid boils. A mixture of liquid and gas exists. Temperature remains constant until all the liquid is boiled off

Evaporation
- evaporation is the change from a liquid to gas below the boiling point
- particles have enough energy to escape as a gas from the surface of the liquid
- volatile liquids evaporate quickly at room temperature

Differences between Boiling and evaporation
- Temperature → Evaporation : any temperature below boiling point
→ Boiling : only at boiling point, temperature remains the constant

- Site → Evaporation : at surface of liquid
→ Boiling : throughout the liquid

- Heat source → Evaporation : no heat source
→ Boiling : heat source present

- Speed → Evaporation : Slow
→ Boiling : Fast

- Similarity : They both result in the change from the liquid to gaseous state

Condensation
- Condensation in the change from a gas to liquid
- When temperature drops : → Gas particles lose K.E.
→ Move closer together
→ Increase in attractive forces
→ Gas becomes liquid

Sublimation
- sublimation is the change from a solid to a gas without melting
- the forces of attraction between particles in a liquid state are too weak to remain in this state
- the temperature remains constant during sublimation, until all the solid has sublimed

Vapour Deposition ( Converting between solid and gas)
- Some substances can change directly from a gas to a solid
- Temperature remains constant during vapour deposition, till all the gas has become a solid

Expansion
- When a substance in the solid state is heated, its particles gain energy and vibrate more vigorously about their fixed positions
- Distance between particles increase
- Causes volume of substance to increase
- As a result, the substance expands

Contraction
- When a substance in the solid state is cooled, its particles can lose energy and vibrate less vigorously about their fixed positions
- Distance between particles decrease
- Causes volume of substance to decrease
- As a result, the substance contracts

Expansion and Contraction
- The number and size of particles in a substance do not change during expansion and contraction
- Thus there is conversion of mass

Diffusion
- Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration

Effect of temperature on the Rate of diffusion
- At higher / lower temperatures, the particles possess greater / lower kinetic energy. Thus, they are able to move faster / slower, resulting in an increased / decreased rate of diffusion

Effect of Particle Mass on the Rate of diffusion
- At a given temperature, heavier / lighter particles require more / less kinetic energy to move at the same speed as lighter / heavier particles.