The Particulate Nature of Matter

 Kinetic Theory: 

 

All substances are made of atoms, which consist of protons, electrons and neutrons.

States of matter:

 

Solid:

1. Strong forces of attraction between particles

2. Have a fixed pattern (lattice)

3. Atoms vibrate but can’t change position therefore fixed volume and shape

Liquid:

1. Weaker attractive forces than solids

2. No fixed pattern, liquids take up the shape of their container but have a fixed volume

3. Particles slide past each other.

Gas:

1. Almost no intermolecular forces

2. Particles are far apart, and move quickly

3. They collide with each other and bounce in all directions. 

Changes of state:

Condensation and solidification: condensation is when a gas turns back into a liquid. When a gas is cooled, the particles lose energy. They move more and more slowly. When they bump in to each other, they do not have enough energy to bounce away again. They stay close together, and a liquid forms. When a liquid cools, the particles slow down even more. Eventually they stop moving except for vibrations and a solid forms. 

 

Evaporation and boiling: evaporation constantly occurs on the surface of liquids. The high energy particles escape from the liquid, even at low temperatures. Boiling occurs at the boiling point (I bet you did not know that) and then the liquid evaporates everywhere in the liquid (not just on the surface) and is much faster. During a change of state the temperature of the mixture does not change.

Diffusion: the process in which particles mix/spread by colliding randomly with each other, and bouncing off in all directions. Particles travel in random zigzag motions, this is how smells spread, solids dissolve, dust particles travel in a random way when suspended in air. 

Evidence for diffusion: 

In liquids: potassium manganate (VII) in a beaker of water. (The colour will spread as a result of Brownian/random motion, this is dissolving.)

 

In gases: a gas jar of air and a gas jar of bromine are connected; the bromine travels up the tube.

Factors that affect the rate of diffusion: 

Temperature increases → rate of diffusion increases

Particle mass decreases → rate of diffusion increases and vice versa (this is shown by the following experiment):

 

Dissolving can be sped up by increasing temperature or stirring