Basics
So what is a solid? Solids are usually hard because their molecules have been packed together. The closer your molecules are, the harder they are. Solids also can hold their own shape.EXAMPLE: A rock will always look like a rock unless something happens to it. The same goes for a diamond. Even when you grind up a solid into a powder, you will see little tiny pieces of that solid under a microscope.
In the same
way that a solid holds its shape, the atoms inside of a solid are not allowed to
move around too much. This is one of the physical
characteristics of solids. Atoms and molecules in liquids and gases are bouncing
and floating around, free to move where they want. The molecules in a solid are
stuck. The atoms still spin and the electrons fly around, but the entire atom
will not change position. Solids can be made up of many things and can have elements or a variety of compounds inside. When you get more than one type of compound in a solid it is called a mixture. Most rocks are mixtures of many different compounds. Concrete is a good example of a manmade mixture.
Crystals
When a
solid is made up of a pure substance and forms slowly, it can become a crystal (Ice).
Not all pure substances form crystals because it is a delicate process. The
atoms are arranged in a regular repeating pattern called a cystal lattice. A
crystal lattice is a very exact organization of atoms. A good example is carbon.
A diamond is a perfect crystal lattice while the graphite arrangement is more
random. 