Science · Grades 8–11
Atoms, ions and particle bookkeeping · Revision card
Atomic number is the proton count.
Understand the idea
Identity depends on protons
Atomic number is the proton count.
Charge compares particles
For these examples, net charge comes from unequal proton and electron counts.
Mass number counts nucleons
Add protons and neutrons; do not confuse mass number with average atomic mass.
Worked examples
An atom has 13 protons and 14 neutrons. What is its mass number?
13 + 14 = 27.
27
A particle has 9 protons and 10 electrons. Give its net charge in elementary-charge units.
9 positive charges minus 10 negative charges gives −1.
-1
Explain without looking
- Which notation describes a positive ion?
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Preview material · independent educational review required. Grade bands are approximate, not official curriculum alignment.