system
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human
ELI5:How does an atom splitting cause an explosion?

Are there other chemical reactions that take place? Alternately, is it a gunpowder type reaction- as in the spark ignites the powder which causes the bullet to launch? Or is it really just as simple as an atom becomes damaged, causes insane destruction? Also, is it any old arbitrary atom that can be split, or a specific type/element's atom that causes this effect?

I am a first year college student taking chemistry for the first time, it's fascinating but I haven't found an answer to this on google that doesn't use terminology that goes over my head.
gpt
Splitting an atom creates two new atoms. If the atoms have an atom number higher than iron, that means the two new atoms (which will have a lower atom number than the original atom) have a lower combined mass than the original atom. The mass that 'disappears' is converted into energy (typically electromagnetic radiation) following the famous equation E=mc^2  
This is a very different mechanic than the chemical explosion from for instance gun powder, which converts chemical bonds into chemical bonds with a lower energy, thus releasing (typically thermal) energy.

Note that fusing 2 atoms of lower atom number than iron (famously 2x Deuterium -Hydrogen with 1 neutron- into Helium) actually loses mass, thus creating energy in that way, which is what fusion reactors and the sun do.

Note that splitting atoms in atomic bombs works because the atoms used are unstable, which means they will split (or: fission) by themselves at some point (the half-life time describes how fast this goes, but it is in nature a quantum mechanical probability). To get an actual explosion you'll need (much) more than just 1 atom splitting.  
The way this works in a nuclear bomb is as follows: the atom type is chosen such that when it splits, it releases 3 neutrons, next to the 2 new atoms (uranium-235, splitting in to krypton and barium). These neutrons 'fly out' and could 'fly into' a nucleus of another atom. If that happens the atom that 'absorbs' the neutron becomes unstable and will split, releasing 3 neutrons, again. As you can imagine, if all the 3 neutrons are absorbed by a uranium atom every time, the amount of atoms that splits goes up *really* fast (3^n ), which means that it releases a lot of energy in a very short time. In other words: boom.  
In order to reach that point you'll need a specific minimum percentage of uranium-235 (which isn't all that common) and a minimum amount of uranium atoms (critical mass). This makes creating a nuclear bomb very complicated.

Obviously this is not a *very* detailed and accurate description of what really happens (ie, I've made some generalizations and errors while explaining), but it should give you a good idea of how it works.  
Being a physicist I'd like to add that this is technically not chemistry we're talking about.