To synthesize in definition is create something chemically. This means that if out of 118 elements, 20 of those are man-made via a nuclear reactor and/or a particle accelerator. These elements are unstable because they are built upon fusing an Atom's nucleus with more proton's than it may usually have which causes the stability to become dangerously chaotic as it is not natural for the element. This is the building block for the Atomic Bombs creation.