MYP Physics States and Properties of Matter, Kinetic Theory Notes

Why Do Scientists Use A Model To Explain The Behaviour Of Matter?

Matter can look and behave very differently, yet the differences can be explained using a single powerful idea - matter is made of tiny particles (atoms or molecules) that move and interact with each other.

Particle Interactions Explain The States Of Matter

1. A useful starting point is the particle model: each substance is made of particles that exert forces on each other over very short distances.
2. When particles are far apart, they exert negligible forces.
3. When particles are close, they attract each other.
4. If pushed too close, they repel each other.
5. Matter commonly exists as solid, liquid, or gas.
6. Each state has different properties because of:
   1. particle spacing,
   2. particle arrangement,
   3. particle motion.

Limits of the Particle Model

1. The particle model does not show individual particles directly.
2. It explains behaviour, not exact particle shapes or sizes.

Solids Have Fixed Positions, High Strength, And Low Compressibility

1. In a solid, particles are tightly packed and occupy fixed positions in an ordered arrangement.
2. They cannot move from place to place, but they can vibrate about their fixed positions.
3. Key properties explained by the particle model:
   1. Solids keep their shape because particles are held in place by strong attractions.
   2. Solids are hard to compress because the particles are already close together; pushing them closer quickly leads to repulsive forces.
   3. It takes energy to separate particles, which is why breaking apart or melting a solid requires energy input.

Liquids Flow But Remain Hard To Compress

1. When a solid is heated, its particles may gain enough energy to break out of fixed positions.
2. The substance becomes a liquid.
3. In a liquid:
   1. Particles are still close together, so liquids are hard to compress.
   2. Particles are arranged more randomly than in a solid and can move around each other.
   3. Attractive forces still matter, so liquids form a definite volume and do not automatically spread out to fill an entire container.

Gases Spread Out And Are Easily Compressed

1. If a liquid is heated further, particles may gain enough energy to overcome attractive forces between them and become a gas.
2. In a gas:
   1. Particles are far apart.
   2. Forces between particles are usually insignificant (except during collisions).
   3. Particles move freely, so a gas fills its container.
   4. Gases are easy to compress because there is lots of empty space between particles.

Changes of State Using the Particle Model

1. Heating a substance gives particles more energy.