THE KINETIC MODEL OF MATTER

What is the Kinetic Model?• A model represents a system in order to help us

understand it.

• Kinetic model represents the constituent particles of matter

• Aids in understanding matter’s behavior, and properties in the different states.

The Kinetic Model of Matter•Matter is made up of tiny particles, atoms or molecules that are always moving.

•Matter can exist in three different states: Solid, Liquid and Gas.

• Arrangement and motion of particles determines matter’s behavior in each state.

The States of MatterMatter can exist as a solid, liquid or a gas. The behavior of a substance in each state is different due to variations in the arrangement and motion of particles in each state.

SOLIDS• Fixed shape• Fixed volume• Incompressible

• Particles packed closely together• Particles held in a regular

arrangement by strong attractive forces

• Particles vibrate in fixed positions• Cannot change their positions

LIQUIDS• Fixed volume• No fixed shape. Take the shape of

their container.• Slightly compressible

• Particles held close together by attractive forces of moderate strength

• Particles vibrate but move freely and randomly within bulk of the liquid

• Particles can slide past each other

GASES• No fixed volume. Volume is same as

volume of container.• Take the shape of their container.• Easily compressible.

• Particles far apart from one another.• Weak or negligible forces of

attraction.

• Particles move freely and randomly at high speeds.

• Particles collide with each other and walls of their container.

Attractive Forces between Particles• Attractive forces hold particles together.• The closer the particles together, the stronger the forces between

them.

• Forces are strongest between particles in solids.• Forces are weaker between particles in liquids.• Very weak or no attractive forces are present between particles in a

gas.

Brownian Motion as Supportive Evidence for the Kinetic ModelThe movement of smoke grains viewed under a microscope in an illuminated chamber serves as supportive evidence for what the kinetic model of matter theorizes about the motion of particles.

Brownian MotionRandom motion of microscopic particles suspended in a fluid.• Smoke inside a cell is viewed through a microscope.• The cell is illuminated using a lamp.• Jerky and erratic path of smoke particles is observed.

• Random movement is caused by repeated and frequent collisions with surrounding, INVISIBLE particles of the air.

Experimental Setup Observation

Changes in the States of MatterChanges in the states of substances can be explained by the kinetic model by carefully considering the attractive forces between particles and the changes in their arrangement and motion.

Changes in State

Melting• Melting is the change in state from solid to liquid.• Occurs at a fixed temperature for a pure substance called the

melting point.

• Melting point of pure ice is .• Upon heating the particles in the solid gain energy and

start vibrating faster. • At the melting point, they have energy to overcome

some of the bonds holding them together and therefore.• Particles break away from each other and lose their

regular arrangement. They are then able to move freely and slide past one another. The solid has melted into a liquid.

BoilingChange in state from liquid to gas at a fixed temperature, called the boiling point for a pure substance. Boiling occurs throughout the liquid. Bubbles of gas start forming deep inside the liquid.

• Boiling point of pure water is • Upon heating, particles in the liquid gain energy

and start moving faster. • At the boiling point, they have enough energy to

overcome almost all of the attractive forces between them. • The particles move far apart from one another

and move randomly at high speeds. The liquid has boiled into a gas.

Boiling

Evaporation• Change in state of a substance from a liquid to gas below its

boiling point.• Occurs at the surface of the liquid.• Occurs at no fixed temperature.

• Some particles in a liquid have higher energy than others.• These particles have enough energy to escape from the surface

of the liquid, as a gas.• Remaining particles are those with lower energy.

Evaporation

Explaining the Cooling Effect of Evaporation• Temperature is a measure of the average kinetic

energy per particle of a substance.• During evaporation, particles with higher energy

escape. • Average kinetic energy of he particles of the

substance decreases.

Explaining Observations About Evaporation

• Rate of evaporation increases with temperature.

• Rate of evaporation increases with surface area.

• Evaporation occurs slowly under humid conditions.Particles of water vapor can enter the liquid from the air.

• Evaporation rate increases under windy conditions.Wind carries evaporated particles away from the liquid. As a result, none of them can fall back into the liquid.

Condensation and Freezing• Upon cooling, particles of a gas lose energy and slow down. • Attractive forces grow stronger and pull the particles close

together eventually, forming a liquid. This is condensation.

• If the liquid is further cooled, the particles gain a regular arrangement as attractions strengthen. This forms a solid. Freezing point is the same as melting point.

Heating and Cooling Curves for Water

The Behavior of GasesThe kinetic model of matter helps us understand, explain and correlate many different properties of gases such as their pressure, volume and temperature.

Gases and Pressure• Gases have no fixed volume or shape. • They expand to fill their container.• Particles are moving randomly at high

speeds and are far apart from one another.

• Particles collide with the walls of the container.• Large number of particles, high

speeds, frequent collisions = high net pressure

Gay-Lussac’s Law of Gases• For a gas with a fixed volume, the pressure of the gas is directly

proportional to its temperature. Container has rigid walls.

• At higher temperature, particles have more energy. • They collide at higher speeds and exert greater force.

𝑝1𝑇1

=𝑝2𝑇 2

Where p is the Pressure and T is the temperature in degrees Kelvin.

Gas Pressure and Temperature

Charle’s Law of Gases• The volume of a gas is directly proportional to its temperature,

provided that its pressure remains constant.

• At higher temperature, the particles have higher energy. • The pressure increases causing the container to expand.

Container does not have rigid walls.

𝑉 1

𝑇 1=𝑉 2

𝑇2

Where V is the volume and T is the temperature in degrees

Kelvin.

Gas Volume and Temperature

Boyle’s Law of Gases• Provided that the temperature of the gas remains constant, its pressure will be

inversely proportional to is volume.

• If the volume of the gas is doubled, there are only half as many collisions on every meter square of the container’s walls. Therefore, pressure halves.

• If volume is halved, twice as many collisions on every square meter of the container’s walls will occur. Therefore, pressure doubles.

Gas Pressure and Volume

KEY POINTS

• Matter is made up of tiny, moving particles.

• Matter can exist in three states – SOLIDS, LIQUIDS and GASES.

• Arrangement and motion of particles is different in each state.

• Brownian motion is the random movement of particles suspended in a fluid and occurs as a result of frequen collisions with the fluid particles. This serves as evidence for the kinetic model.

KEY POINTS

KEY POINTS

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