This is nuclear physics.
When an atom gains a proton it is 'fusion'.
When an atom loses a proton it is 'fission'.
e.g. Using heavy hydrogen (deuterium)
[2/1]H + [2/1] = [4/2]He
This is very simple nuclear fusion, which is going on in the Sun.
Using Uranium - 236
This disintegrates into plutonium and a neutron ; this is nuclear fission and goes on into nuclear reactors (in power stations), on Earth or Atom Bombs.
This is called a redox reaction. An atom that loses an electron is oxidized and an atom that gains an electron is reduced.
covalent/ionic bonding.
Ion. Any atom that loses or gains an electron becomes an ion.
An atom that loses electrons becomes a positively charged ion called a cation. An atom that gains electrons becomes a negatively charged ion called an anion.
Ion. Any atom that loses or gains an electron becomes an ion.
A neutral atom that gains or loses electrons is now an ION. If it loses electrons to become M^(n+), then it is a CATION. If it gains electrons to become X^(n-), then it is an ANION. NB Atoms that gain or lose electrons are no longer atoms , but IONS.
covalent/ionic bonding.
the number of protons in an atom is what determines which element the atom is. So if an atom "lost" a proton, it would become another element entirely.
An ION . Metal (M) ionises ( loses electrons) M(g) = M^(n-) + ne^(-) M^(n+) is a CATION . Non-metal (X) has electron affinity ( gains electrons) X(g) + ne^(-) = X^(n-) X^(n-) is an ANION .
When an atom loses or gains electrons, it becomes an ion.
an atom that gains an electron becomes a negative ion, called an anion.
When an atom actually gains a neutron from outside it is called neutron capture. Atoms almost never emit neutrons (except when high energy processes happen). Most cases of "gain or loss" of neutrons by an atom happen entirely inside the nucleus, when the process of Beta decay converts a proton to or from a neutron.