Kinetic Model Of Matter

Kinetic Model of MatterKinetic Model of Matter 1

State of Matter

Matter is made up of a tiny particles called atomsatoms and moleculesmolecules. These particles are much too small to be seen by human eyes.

Ice, water and steam are three different Ice, water and steam are three different states of matter of the same material. states of matter of the same material.

The three states of matter are called solid, The three states of matter are called solid, liquid and gas.liquid and gas.

Kinetic Model of Matter 2

Solid

Properties Fixed shape and fixed volumeNot compressibleDoes not flow easily

Distance between moleculesThe molecules are arranged close together in a

regular pattern.Solids cannot be compressed because the

molecules are arranged closed together and there is little space between them.


Forces between molecules/ Motion of the moleculesThere are balanced forces between the molecules

which hold them in fixed positions.The molecules can only vibrate about their fixed

positions alternately attracting and repelling one another.

The strong attractive forces prevent the molecules from leaving their positions while the repulsive forces which act when they are too close to each other prevent them from collapsing. This explains why a solid has a fixed shape and a fixed volume.

When a solid is heated, the molecules gain energy and vibrate. The separation between molecules increases slightly and the solid expands.


Liquid Properties

Fixed volume but no fixed shapeAssumes the shape of the container which it

occupiesNot easily compressibleFlows easily

Distance between moleculesThe molecules are not arranged in a regular pattern

and are slightly further apart than in solids.Liquids cannot be compressed as the molecules are

close together and there is little space between them.


Forces between them/ Motion of the moleculesThe molecules also vibrate to and fro, alternately

attracting and repelling one another with forces which can be just as strong as those in solid.

Though there is still forces between the molecules, they are not held in fixed position. Because of this, the molecules move among one another throughout the liquid. That is why liquids flow and take the shape of their container.

The attractive forces between the molecules make it difficult for the molecules to leave the liquid and thus liquids have a definite volume.

When a liquid is heated the molecules vibrate and move about vigorously. Thus the liquid expands slightly only to a very slight extent.


Gas

PropertiesNo fixed shape and no fixed volumeAssumes the shape and volume of its containerHighly compressibleFlows easily

Distance between moleculesThe molecules are far apart.A gas can be compressed because the

molecules are sparse and there is a lot of space between them.


Forces between them/ Motion of the moleculesThe molecules move randomly at high speed,

colliding with one another and with the walls of the container.

The intermolecular forces act only at moments of collision. Otherwise, the molecules are so far apart the intermolecular forces become negligible. Therefore, a gas is free to fill a container completely.


Brownian Motion

Brownian motion is named after Scottish botanist Robert Brown who first observed it in 1827.

He used a microscope to study tiny grains of pollen suspended in water.

He noticed that the grains were constantly moving in a random manner.



• Brownian motion can also be seen when using a microscope to look at smoke particles floating in the air.

• The smoke particles are seen to move continuously and haphazardly.


• He suggested that the irregular or random motion of smoke particles was the result of smoke particles being hit by unseen, fast moving air molecules.

• Hence Brownian motion provides evidence of the movement of molecules.

• In 1905 Einstein was able to explain how Brownian motion takes place.

Kinetic Model

The kinetic theory of matter states that all matter is made up of a large number of tiny atoms or molecules which are in continuous motion.

The existence of particles in continuous motion has been demonstrated by Brownian motion and diffusion.


Motion of Molecules and Temperature In Brownian motion demonstration we can see

that when the temperature is higher, the motion of smoke particles in the air become more vigorous.

This is because the surrounding air particles are moving faster and hitting the smoke particles more frequently and with greater force.

When temperature increases, thermal energy is transferred to the molecules and the molecules gain kinetic energy. Hence the molecules move faster.


Motion of Molecules and Pressure When randomly moving gas

molecules hit the wall of a container they exert a force on the wall.

As the pressure is defined as force per unit area, the force acting in the container gives rise the gas pressure.


Pressure against Temperature For fixed mass of gas at constant

volume;As temperature of gas in container

increases, the molecules move faster and hit the walls more frequently and more violently.

Gas pressure increases with gas temperature and vice versa at constant volume.


Volume against Temperature When temperature of the gas container

increases, the molecules move faster and hit the walls more frequently and with greater force.

This causes the pressure to increase. At constant pressure, the volume of gas

increases with increasing temperature and vice versa.


Pressure against Volume

If we half the volume of container, the number of molecules hitting the wall in one second will also be double.

At constant temperature, gas pressure increases when volume decreases.


Kinetic Model Of Matter

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