Chemistry · Grades 7–10
Atoms, isotopes and ions · Revision sheet
Track protons, neutrons and electrons separately.
Learn the idea
Identity
Atomic number Z counts protons and identifies an element.
Mass number
For one isotope, A = protons + neutrons. This is not a weighted periodic-table atomic mass.
Charge
For these simple ions, charge number = protons − electrons.
Isotopes
Atoms of one element can have different neutron counts while retaining the same proton count.
Explain without looking
- A nucleus has 17 protons and 20 neutrons. What is its mass number?
- Correct the claim that losing an electron turns sodium into a different element.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.