Thanks to all commenters for the assistance. Here are my combined notes for how the spell will work. Once I actually publish the game, I will add a link below, in case anyone wants to try it out.
Convert element notes
There are several approaches to elemental conversion, but all require a common body of knowledge which is encapsulated in this spell. Therefore each method is a sub-spell, but all are learned at once in a bundle with a combined total difficulty level of 30.
The casting difficulties and magic points costs will vary (TBD)
The approaches are:
Proton Binding/Isotope, Hydrogen Binding, Alpha Decay, Beta Decay, Dematerialize
Ionize is also learned in this bundle, although it isn’t actually elemental conversion per se.
Proton Binding - Remove Proton
The simplest form of elemental conversion is to drop from one element to the next lower element by number. (refer to the standard the periodic table of elements) (For example from He to H). This can be accomplished by simply getting rid of one proton from the source element. Highly explosive ionized Hydrogen isotopes will be formed as a byproduct of this type of conversion. If you don’t want an explosion, you can dump the extra protons to the beyond using “Banish Object”. (requires an open Portal)
Proton Binding - Add Proton
The opposite process can be used to add a proton and go up a number on the periodic table. This only works if you happen to have a lot of extra protons handy. (perhaps you previously stored some in the beyond?)
Adding or removing protons from an atomic nucleus is very energy intensive
A side effect of the proton binding method is that the target element will actually be an isotope because its neutron count will not match its proton count. Isotopes may be radioactive and therefore, repeat or extended exposure can cause burns and or disease.
Isotopes can also be created directly, without elemental conversion, by adding or subtracting neutrons to a target. In the case of removing neutrons, the free neutron byproducts are themselves an ionizing radiation hazard.
Hydrogen Binding is similar to Proton Binding except that instead of only moving protons, you also move neutrons and electrons. This takes marginally more energy, but results in a slightly more stable byproduct of plain old hydrogen. It is flammable, but it won’t immediately explode, unless you are standing near an open flame. Also, hydrogen atoms can be attained by regular chemical processes or by Arrange Atoms.
Alpha Decay is similar to hydrogen binding, but is actually Helium Binding. The advantage to this technique is that it takes advantage of a natural lowering of stability, so that an element can be converted to an atomic number Lower by 2 elements, at a greatly reduced Magic Point cost. The byproduct is Helium, which is stable and not flammable. This method can not be used for Increasing atomic number.
Beta Decay is the conversion between protons and neutrons. Therefore you can either increase or decrease in atomic number, but the target element will be an ionized isotope. This is only slightly less costly in terms of MP than Proton Binding
Dematerialize is accomplished by banishing the entire source matter, then bringing back only the correct particles to produce exactly the desired element. No undesired byproducts are produced. If you are meticulous recordkeeper, you can keep track of remaining materials in storage in the beyond for future use.
Ions are created by adding or removing electrons. Ionization greatly affects an atom's likelihood of bonding chemically with neighboring molecules. Thus an Ionization spell may result in a wide variety of unintended changes in state, solubility, corrosion, metalization, etc., often times resulting in objects turning to powder or gas.
Practical Tips for Convert Element
To practice, use readily available elements. A great practice case is N to C as both are very common, and it will be easy to see if it worked as it will convert from a gas to a dark powdery substance. You will be dumping one proton in seven. Remember, you will need to do this on millions of molecules to make a measurable change.