Like all from 100 to 115 on the periodic table are made in labs. What does this mean and how is it done? And if we can do it, why havent they been created in nature already? Also, is there any reason to think that a elemnt cannot be a atomic number of, say, 250 or 700?
You bombard a heavy elements with neutrons, protons, and or alpha particles. These elements are so unstable that they have absurdly short halflifes. So these elements were probably formed in supernovas, but they have all decayed away. The stronge force is very short range and the electrostatic force is long range so the electrostatic repulsion of the protons does not allow massive nuclei to form, they will simply not hold together.
So it is indeed that simple. I read about an element with the half life of 3.6 seconds, it must be one of these. Ok, but, The strong force is active between each adjacent protons/ neutrons. Wont they all hold together coz of the attraction of the nearest protons/neutrons? After a while of course this will be overridden by the electronmagnetic force so around what number is this? 120? 150?
Stability of the elements is more complicated than that but it is useful to simply look at the stong force and the repulsive force of the protons as a way to understand what is going on. U235 has a halflife of 700 MY and U238 has a halflife of 4.5 BY, which shows that the size of the nucleus is not the only factor. Most of the heavier elements are unstable - that is why they are radioactive.