Why do some things explode?

I am now going to discuss with you the question that baffles most teens and kids: How do things explode?
There are many different kinds of explosions. One kind of explosion is one that can happen with rare metals such as alkali metals. Here is a link that will show you examples of some: http://www.youtube.com/watch?v=cqeVEFFzz7E
The metals being used in this video react because when the water hits the metal, it makes the molecules in the metal react and eventually it is so combusted and there is so much pressure that eventually the substance explodes because of the electrons being given off.
Another type of explosion is one that would have to do with gas. In this explosion, fire would touch the gas and heat the electrons and protons so that they would be under so much pressure that eventually it would explode in an enclosed area. Remember, the smaller the enclosed area, the bigger the explosion (in most cases). This is because the substance is under greater pressure.

Substances explode because of different things they react with that could effect the molecules and electrons in the atom and make it explode.

A more complex example of an explosion is sodium and water.

Sodium wants to give away one electron to be stable. It is very reactive with water.

(Na+H2O-NaOH+H2+little energy.)

Once that sparks a little in the water, it is enough to cause one of these reactions:

(H2+O2-H2O+energy) (energy being the explosion)

(H2=hydrogen gas O2=oxygen gas)

When hydrogen gas and oxygen gas combine together, they react with water making an explosion.

Explosions happen because of the matter or element giving off electrons to become stable. If these elements react with water, the formula i have stated above shows what will happen.

*The picture i have shown above (Top right) is a very good example of what i am talking about.