[greeniemax (OP)]

Its funny that if you change the number of electrons in an atom it becomes an ion.

But if you change number of neutrons it becomes an isotope.

That means only thing that determines atom to be of certain type is proton, but neutron is actually a collapsed proton with electron, how come it doesn't make changes in the structure of the atom?

[Nizzle]

A neutron is not a collapsed proton with electron, a neutron is one up-quark with two down-quarks, while a proton is two up-quarks with one down-quark.

To answer your question: The number of protons indeed defines what atom it is, and if you change the number of electrons you get ions, and if you change the number of neutrons you get isotopes.

[Soul Surfer]

The point is that the properties of atoms that we are aware of on a day to day basis (chemistry)are those of the outer shells of electrons and nothing else. The atomic nucleus has no effect other than to define the number of electrons that make the atom neutral which is its normal state.

[Nizzle]

The point is that the properties of atoms that we are aware of on a day to day basis (chemistry)are those of the outer shells of electrons and nothing else. The atomic nucleus has no effect other than to define the number of electrons that make the atom neutral which is its normal state.

Not exactly Soul Surfer, surely you cannot state that an Oxygen atom behaves the same as a Sulphur atom, while they do have the same amount of electrons  on the outer shell.

Next to the # of electrons on the outer shell, also the # of shells or "distance from outer shell to nucleus" is important (expressed in Electronegativity)

[Soul Surfer]

Nizzle please note I said shells not shell to deflect that pedantic argument.  I agree that the fine detail depends on the total number of electrons.  The questioner was talking simplistically about changes to the nuclear structure.  And you were talking about the number of protons in the nucleus but from everyday chemistry it is the electrons that are the important bits.