Question

What are the protons, neutrons, and electrons for a sulfur(2-) anion with a mass number of 33?

Answer 1

Well, number of protons is easy. It's `"sulfur, Z = 16",` so there are 16 `"nucular protons"`.

Explanation:

If there are 16 positively charged particles, there must be 16 negatively charged particles in the `"neutral"` element. We have `S^(2-)`, and thus there must be `18` electrons associated with the ion.

And neutrons for `""^33S`? Well, the electrons are along for the ride, and have zero rest mass. The mass of an atom, to a first approximation, is the number of massive, nuclear particles, i.e. the number of `"protons and neutrons"`. We have `16` nuclear protons, so there MUST BE `17` `"neutrons"`, i.e.

`33_("the mass number")=16_("protons")+17_("neutrons")`.

Are you happy with this? If you think it is simple, it should be, but many students are unconvinced by this apparent simplcity.

From where did I get these numbers?