GCSE Biology: Paricle Theory

Solid

Solid

The molecules in a solid are close together and have very strong bonds. The particles move very little.

Liquid

Liquid

The molecules are slightly further away and have some freedom. They take the shape of the container they are in.

Gas

Gas

The molecules in a gas have a lot of freedom and the bonds are very wek. They expand to fill the container they are placed in by dispersion.

Diffusion

Diffusion is the tendancy for molecules to become evenly distributed throughout the space that they occupy. In diffusion molecules are moving from an area of high concentration to an area of low concentration, down a concentration gradient.

Gas

A net movement of particles from a region of higher concentration to a region of lower concentration. In the perfume experiment, perfume was sprayed in the corner of the room and then it diffused around the room. The people nearest to the perfume smelt the perfume first, and the molecules of perfume collided with the air molecules and the smell diffused around the room. In the potassium permanganate experiement potassium permanaganate was placed in water and the dark purple which we origionally saw became lighter as it diffused around the container. To speed up the diffusion process man-made wind or stirring could be used. This would increase the rate of diffusion as it "pushes" the particles around. Heating would make the particles move about quicker and so also increase the rate of diffusion.