well duh il explain nice and slow
Atomic bombs are the type of nuclear bomb which rely on the process of fission, or rapid splitting of an atom's nucleus, to produce an explosion. The "atom" or "A" bomb uses fission of uranium or plutonium in a single step reaction, rather than multiple steps, to achieve its effect. They are the simpler form of nuclear weapon.
This is in contrast to the other type, the so-called thermonuclear bomb, which is also known as a hydrogen or "H" bomb. Hydrogen bombs use the process of fusion, or combining atoms, in addition to fission. A hydrogen bomb involves the fusion of a hydrogen isotope on an atomic scale by way of steps of mutiple reactions thus yielding a much more powerful explosion upwards of 500 million tons of TNT. Thus hydrogen bombs contain part of the same fission reaction as an atomic bomb, but also have a more powerful reaction of fusion in addition.