The Alkali Metals are the exact opposite of the Noble Gases. While the gases are inert, do not react, and altogether, well, Noble, the Alkali metals are fun, loud, and explosive. The Alkali metals consist of Lithium, Sodium, Potassium, Rubidium, and Cesium.
You have probably heard of what happens when you throw any Alkali Metal in water: Boom
So how does this all work?
First of all, the Alkali Metals all oxidize very quickly, meaning they grab the Oxygen around them and coat themselves with an Oxygen compound.
Second of all, the Alkali metals are significant because each atom has one extra electron far away from the nucleus. And when put into water, they discover that there is more Oxygen here than in the air, and so they grab onto the Oxygen as fast as they can, the Oxygen grabs back, and that one extra electron, being so far out, has little attraction to the nucleus. The nucleus is the positively charged center of the Atom, and electrons are negatively charged particles floating around it, and everything is held together because of the charge. And so the poor little electron gets pulled over to the Oxygen. And Hydrogen. (As you know, water is H2O).
Now, the farther the electrons are from the nucleus, the higher energy they contain. When the electron is pulled away from it’s home, it releases that energy, and energy is the same thing as light. And heat. You all know from a previous post, What is fire? that fuel (the Hydrogen) + an oxidizer (the oxygen, of course) + a heat source = Well, it all depends on the fuel, if it is Carbon in the form of wood or paper, you get fire. If it is Hydrogen, well, you remember the Hindenburg. It was full of Hydrogen gas