These questions ask whether a change creates an isotope, an ion or a different element, and how to find the sign of an ion's charge. Follow the particle that changes instead of relying on the words positive, negative, loss or gain alone.
Separate nuclear identity from electric charge
Make a three-row record for protons, neutrons and electrons. A proton change changes the element. With protons fixed, a neutron change gives a different isotope and a different mass number. With the nucleus fixed, an electron change gives an ion. For example, a particle with eleven protons and ten electrons has charge +1 because 11 minus 10 equals +1; it is still the element identified by eleven protons.
| Observation | Conclusion |
|---|---|
| Same protons, different neutrons | Isotopes of the same element. Name one as element-name followed by a hyphen and its mass number. |
| Same protons and electrons | The particle is electrically neutral. |
| Fewer electrons than protons | Positive charge; electron loss produces a cation. |
| More electrons than protons | Negative charge; electron gain produces an anion. |
| Charge calculation | Use protons minus electrons. A positive result means an electron shortage; a negative result means an electron excess. |
Neutral isotopes of one element normally have the same electron arrangement, so their ordinary chemical behaviour is nearly the same even though their masses differ. Nuclear stability is a separate question: some isotopes are stable and some are radioactive. Adding or removing an electron does not by itself transform or destabilise the nucleus.
Do not swap the roles of the particles
| Trap | How to reject it |
|---|---|
| Putting atomic number or charge into an isotope name | The hyphenated number is the mass number. Ionic charge is written and interpreted separately from isotope naming. |
| Assuming different neutrons create a new chemical family or guarantee radioactivity | Fixed protons preserve the element, and fixed neutral electron arrangements preserve nearly the same ordinary chemistry. Stability must be considered separately. |
| Calling a charged particle electron-free or blaming neutrons | An ion needs unequal proton and electron counts, not zero electrons and not a neutron change. |
| Reversing loss and gain | Losing negative charge leaves a positive cation; gaining negative charge makes a negative anion. |
| Reading a plus sign as extra electrons | A 2+ ion has an electron shortage of two, whereas a 1- ion has one electron more than its proton count. |
| Equating ionization with nuclear radioactivity | Ionization changes the electron shell. It neither changes isotope identity nor makes a stable nucleus radioactive by itself. |
Try it
Which description correctly defines isotopes of a single element?
- Same proton count but different neutron counts
- Different proton counts but the same element name
- Same neutrons but necessarily different elements
- Different electron counts only, regardless of nuclei
A monatomic ion contains 17 protons and 18 electrons. Enter its charge number as a signed integer.
An atom becomes an ion through ordinary electron loss. Which statements about what changes are correct? Select all that apply.
- Its proton count changes.
- Its electron count changes.
- Its mass number changes.
- Its isotope identity stays the same.