TOPIC 1. THE PARTICULATE NATURE OF MATTER

Matter is anything that has mass and occupies space. There are 3 states of matter, solids, liquids and gases. (Plasma is the 4^th state of matter which is not included in the CIE syllabus).

Solids:

· The particles are packed closely together. · The particles cannot move freely but can only vibrate in a fixed position. · Solids can be transformed into liquids by melting, and liquids can be transformed into solids by freezing. · Example of solids: wood, metals (accept mercury), crystals, rubber etc.

Liquids:

· Liquids cannot be compressed and  able to conform to the shape of its container. · This means that the shape of a liquid is not definite but is determined by its container. · Example of Liquids: water (H2O), oil etc.

Gases:

·  A gas can be compressed. Not only will a gas conform to the shape of its container but it will also expand to fill the container. · In a gas, the molecules have enough kinetic energy so that the effect of forces is small, and the typical distance between neighboring molecules is much greater than the molecular size. ·  A liquid may be converted to a gas by heating to the boiling point.

The Kinetic Theory of Matter

   The theory explains the behaviour of matter and their physical properties. Kinetic means movement, and so kinetic energy means movement energy

The kinetic theory of matter states:

• Each matter has a different type of particles with different size and mass.
• Particles are in continuous movement.
• The speed of movement depends on the mass of the particle, temperature and several other factors that you will know later on.

Comparing Properties of Solids, Liquids and Gases:

Molecular Structure	Solid	Liquid	Gas
Particles Arrangement	Very closely packed	Closely packed	Very far apart
Intermolecular Forces	Extremely strong	Not weak Weaker than in solids	Very weak
Movement of Particles	Vibrating in a fixed position	Slowly slide over each other randomly	Moving randomly
Compressibility	Cannot be compressed	Can be hardly compressed	Very compressible
Diffusion	Cannot diffuse	Diffuses slowly	Diffuses quickly

 

Physical Changes (Change in State)

·         Physical changes are changes in which no new substance is formed.

·         For example melting and ice cube or dissolving salt in water.

·         Physical changes are reversible. For instance if you heat and melt and ice cube to water, you can put it in a freezer and have it changed back to ice.

Changing the state of a matter is a physical change. And it is done by either heating or cooling. The following diagram represents changes in state:

1. Melting: The change of state from solid to liquid. The temperature at which a solid melts is called the melting point.

2. Evaporation: The change of state from liquid to gas. The temperature at which a liquid evaporates is called the boiling point.

3. Sublimation: Substances that turn from solid to gaseous state or from gaseous state to solid state, without changing into a liquid. Example Iodine, dry ice (solid carbon dioxide)

Melting occurs when you heat a solid.

• Heating gives the particles more kinetic energy making them move faster and further.

• Until at some point they have enough energy to overcome the forces of attraction between the particles changing into a liquid.

Boiling occurs when you heat a liquid.

• Heating the liquid, particles will gain even more kinetic energy and start moving even faster, pushing each other away.

• The particles have highest amount of energy that they can break the forces of attraction and escape as a gas; this is the start of boiling. 

On the other hand, cooling a gas will make its particles lose their kinetic energy and move closer and slower. Eventually the forces of attraction will hold them together forming a liquid (condensation). And if a liquid is cooled, its particles will move closer and slower until the forces of attraction are strong enough to hold them tight together forming a solid (freezing).

During the process of melting and boiling the temperature remain constant, because the energy is used to break the bonds between the particles. 

Heating curve

· The following figure is a heating curve of a solid.

· At point ‘A’ the state is solid.

· At point ‘B’ the solid is melting; it is a mixture of solid and liquid.

· At point ‘C’ the state is liquid.

· At point ‘D’ the liquid is evaporating, it is a mixture of liquid and gas.

· At point ‘E’ the state is gas.

· Temperature ‘X’ is the melting point while temperature ‘Y’ is the boiling point.

Cooling Curve

· The following figure is a cooling curve of a gas.

· At point ‘A’ the state is gas.

· At point ‘B’ the gas is condensing; the state is a mixture of gas and liquid.

· At point ‘C’ the state is liquid.

· At point ‘D’ the liquid is freezing, the state is a mixture of liquid and solid.

· At point ‘E’ the state is solid.

· Temperature ‘X’ is the melting point and temperature ‘Y’ is the boiling point.

    The purity of substances can be easily determined by testing its boiling and melting points. This is because pure substances have sharp boiling and melting points, while those of impure substances have range of boiling and melting points. Example pure water has m.p. of 0^oC and b.p. of 100^oC.

Diffusion

     Diffusion is the random movement of particles to fill the available space and spread evenly. For instance, if you pass by a trash can, you can smell the ugly scent of trash. This is because molecules from the garbage diffused out of the can to the air which you breathed in.

Diffusion rate depends on several factors, these are:

• Mass of the substance. The lighter the substance (lower M_r or A_r) the faster it diffuses
• Temperature. The more kinetic energy the particles have, the faster they move and diffuse.