MYP Chemistry States and Properties of Matter Notes

The Particle Model Explains the Behavior of All States of Matter

The particle model of matter is a simplified but powerful framework for understanding the behavior of solids, liquids and gases on a microscopic level.

At its core, the model assumes that:

1. All substances are made of tiny particles
   1. These particles may be atoms, molecules or ions.
2. Particles are in constant motion
   1. The higher the temperature, the faster the particles move (they have more kinetic energy).
3. Forces of attraction exist between particles
   1. These forces can be stronger or weaker, holding particles closely together (as in many solids) or allowing them to move more freely (as in liquids and gases).
4. There are spaces between particles
   1. The amount of space between particles helps explain properties such as density and compressibility.

The Relationship Between Particle Arrangements and Properties

Understanding how particles are arranged and how they move helps explain three key properties of solids, liquids and gases:

1. Density
2. Compressibility
3. Diffusion

You can think about the three states of matter like this:

Density

$$
\text { Density }=\frac{\text { mass }}{\text { volume }}
$$

1. In solids, particles are packed closely together, so solids often have high density.
2. Liquids are usually slightly less dense than solids because there is a little more space between particles.
3. Gases have very low density because their particles are far apart.

Compressibility

1. In solids, particles are locked in fixed, close positions with very little empty space between them. Solids are therefore almost incompressible.
2. Liquids also have particles close together, with only slightly more space than in solids, so they are nearly incompressible.
3. In gases, particles are widely spaced, so they can be pushed closer together. Gases are therefore highly compressible.

Diffusion

1. In solids, diffusion is extremely slow because particles can only vibrate in fixed positions.
2. In liquids, diffusion occurs slowly as particles can slide past each other.
3. In gases, diffusion is rapid because particles have high kinetic energy and large spaces between them, allowing them to spread out quickly.

The Kinetic Theory Explains Particle Motion

The kinetic theory of gases extends the particle model to explain the behaviour of gases in terms of the motion of their particles.

It states that:

1. Gas particles are in random, constant motion.
   1. They move in straight lines until they collide with each other or with the walls of the container.
2. Collisions between gas particles are (ideally) perfectly elastic.
   1. In a perfectly elastic collision, no kinetic energy is lost overall.