The Particulate nature of matter
1) State the distinguishing properties of Solids, Liquids and Gases
- Solid: Particles in a solid have regular arrangement and are close together. The particles are vibrating in their fixed position.
- Liquid: Particles in a liquid have a random arrangement and are close together. The particles can slide over one another.
- Gas: Particles in a gas have a random arrangement and are far apart. The particles are constantly moving in a random motion.
2) Describe the structure of Solids, Liquids and Gases in terms of particle separation, arrangement and types of motion
3) Describe the changes of state in terms of melting, boiling, evaporation, freezing and condensation
- Melting: The substance changes state from solid to liquid.
- Boiling: The substance changes state from liquid to gas at a fixed temperature.
- Evaporation: The substance changes state from liquid to gas over a wide range of temperatures. Evaporation can occur at any temperature. Occurs only at the surface of the liquid.
- Freezing: The substance changes state from liquid to solid.
- Condensation: The substance changes state from gas to liquid.
4) Define terms Atom, Molecule and Ion
- Atoms: are the building block for all substances. They possess a nucleus made of protons and neutrons, with electrons orbiting the nucleus.
- Molecules: are structures made of two or more atoms chemically bonded together.
- Ions: are atoms or molecules with an overall positive or overall negative charge. This happens when the number of protons and electrons in the atom or molecule are not equal.
5) Explain changes of state in terms of particle theory and the energy changes involved
- When a substance is heated, we provide it with heat energy. As the particles of the substance absorb this energy, they move faster.
- When a substance is cooled, it loses its energy to its surroundings, so the particles move less.
- When the solid is heated, the particles gain energy and vibrate more vigorously. Eventually, they vibrate so vigorously that the particles are forced apart from the strong attractive forces. The temperature that this occurs at is called the melting point. Now the attraction between them is weaker, allowing the particles to slide over one another. The substance is now a liquid. This process is called melting.
- As the liquid is heated, the particles gain energy until they all move so vigorously that they enough energy required to break free of the bonds holding the particles together. The temperature that this happens at is called the boiling point of that liquid. The particles can now move randomly in any direction at high speeds, making the substance a gas. This process is called boiling.
- As a gas is cooled, its particles lose energy to their surroundings. This means they move less vigorously, allowing the attraction between the particles to have a stronger effect. This forces the particles closer together and limits their motion to sliding over each other. This makes the substance a liquid. This process is called condensation.
- As a liquid is cooled, its particles lose energy to its surroundings. The particles move less vigorously, allowing the attraction between them to have a stronger effect, meaning they are held closer together. As a result, the particles become packed tightly together in a regular arrangement and can only vibrate around a fixed point. As a result, this substance is now a solid. This process is called freezing or solidification.
Evaporation is similar to boiling in that it describes the change of state from liquid to gas, however
- Evaporation can occur at any temperature between the melting and boiling point of the liquid.
- In a liquid, particles gain energy from their surroundings, allowing them to move more vigorously, until the particles at the surface of the liquid gain enough energy to break away as a gas.
6) Describe and explain Diffusion in terms of the movement of particles
- Due to the random motion of particles, fluid substances (gases or liquids), tend to spread out as much as they can. So if there’s more of one type of particle in one area, it will tend to spread out until the particle is evenly distributed throughout the area.
Concentration is a measure of how much of a substance there is in a single area, in other words, the amount of substance per unit volume.
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration down the concentration gradient.
* 7) Describe and explain Brownian Motion
- Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion. They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.
- Botanist Robert Brown used a microscope to look at pollen grains moving randomly in water to conclude this.
8) Describe and explain dependence of rate of diffusion on molecular mass
- The smaller the molecular mass, the less energy it needs to move, the greater the rate of diffusion.