How many combinations can you have of protons/neutrons/electrons?

[Achilles]

For instance hydrogen atom I think has 1 proton and 1 electron. Can you have 1 proton and 2 electrons, what is that called? Can you just add electrons or protons or neutrons to an atom or is that not allowed due to the laws of nature.

[Sensei]

6 minutes ago, Achilles said:

Can you have 1 proton and 2 electrons, what is that called?

It's called Hydride

https://en.wikipedia.org/wiki/Hydride

 

[Strange]

2 minutes ago, Achilles said:

For instance hydrogen atom I think has 1 proton and 1 electron. Can you have 1 proton and 2 electrons, what is that called? Can you just add electrons or protons or neutrons to an atom or is that not allowed due to the laws of nature.

An atom always has the same number of protons and neutrons, because it has to be electrically neutral. However, there can be varying numbers of neutrons (within some range) in atoms (these are called isotopes). So, for example, hydrogen has 1 proton and 1 electron but can have 0 (hydrogen), 1 (deuterium) or 2 (tritium) neutrons.

There are 118 elements in the periodic table. But only 94 occur in nature (the others are too unstable). https://en.wikipedia.org/wiki/Periodic_table

There are 253 stable isotopes of all the different atoms: https://en.wikipedia.org/wiki/Isotope

And atom can temporarily lose (or possibly gain) one or more electrons, to form an ion but, again, these are not stable and quickly gain (or lose) the electron(s) to revert to an atom.

 

[Sensei]

16 minutes ago, Achilles said:

Can you just add electrons or protons or neutrons to an atom or is that not allowed due to the laws of nature.

There is limit how many additional electrons can have atom or molecule.

After proton-capture or neutron-capture nucleus can become radioactive, unstable, and decay.

Edited August 17, 2018 by Sensei

[swansont]

5 hours ago, Achilles said:

Can you just add electrons or protons or neutrons to an atom or is that not allowed due to the laws of nature.

You can add protons or neutrons, but most results would be unstable. There are also combinations which will not occur, since a bound state can't be achieved, e.g. two protons, but those details depend on nuclear structure (i.e. not simple)