# S-Cool Revision Summary

## S-Cool Revision Summary

Everything around us is made up of particles.

The movement of different particles amongst each other, so that they become
evenly mixed, is called diffusion.

The random motion of particles is called Brownian
Motion
. This 'random walk' is caused by particles colliding
into each other and their container wall.

Solids, liquids and gases are the Three States
of Matter
.

The particles in a solid are tightly packed in a fixed position.
They do vibrate in their fixed positions. This is why a solid has a fixed volume
and shape and cannot be compressed.

The particles in a liquid are close together but can move
around and slide past each other. This is why a liquid can change its
shape but not its volume. A liquid cannot be compressed.

The particles in a gas are far apart, and they move around
very quickly
. Therefore, a gas has no fixed shape or volume and can easily
be compressed.

It is possible for a substance to change from one state to another. Changing
state depends on the temperature of the substance.

• Solid to liquid: Melting.

• Liquid to gas: Evaporating.

• Gas to liquid: Condensing.

• Liquid to solid: Solidifying.

Some substances can go from solid to a gas - this is called sublimation.

If the volume of a gas is kept constant, its pressure increases with temperature.

When a gas is compressed into a smaller volume, its pressure increases.

If the pressure of a gas is constant, its volume increases with temperature.

When a solute (solid) dissolves in a solvent
(liquid) the product is called a solution.

A saturated solution
is one that can dissolve no more solute at that temperature. Raising
the temperature of a solution increases the solubility of the solute.

To separate a solid from a liquid four methods can be used :

1. Filtering.

2. Centrifuging.

3. Evaporating.

4. Crystallizing.

To separate a solvent from solution you use simple
distillation
.

To separate two liquids, fractional distillation
is used.

To separate a mixture of coloured substances we use chromatography.

A single particle is called an atom.

Atoms contain three particles, neutrons, protons and electrons.

Protons(+) and neutrons are located in the nucleus
of the atom. The electrons (-) whiz around the nucleus in orbits called energy
shells/levels.

The first shell can hold only 2 electrons, the second 8 electrons and the third
8 electrons.

Electrons have a negligible mass in comparison with protons and neutrons that
carry the same mass.

The proton number is the number of protons in the
nucleus of an atom.

The mass number is the number of protons and neutrons
in the nucleus of an atom.

An atom contains the same number of electrons and protons. Since these two
particles have opposing charges, an atom overall is neutrally charged.

An element consists of only one type of atom.

A compound is made up from two or more types of
atom bonded together.