Protons, Neutrons, Electrons, Elements and Compounds
From the basic structure of the atom to isotopes, this exam covers everything you need to know about matter at the subatomic level. Primary tackles essential concepts; Secondary goes deeper with atomic number, mass number and the difference between element and compound.
Everything that exists is made of atoms: understanding their structure —a nucleus with protons and neutrons, electrons orbiting around it— is the foundation of all chemistry and much of physics. It is one of those topics that, once truly understood, makes the rest of the subject click into place.
Primary school covers the essential concepts (nucleus, electrons, molecules as bonded atoms). Secondary goes deeper with atomic number (Z), mass number (A), calculating neutrons (N = A − Z) and isotopes —same element, different number of neutrons— plus the difference between element and compound.
Practise everything from the basics to isotopes with the exam below, with a reasoned explanation for every answer.
Physics & Chemistry · Primary, Secondary
Primary learns that atoms have a nucleus and electrons, that molecules are bonded atoms. Secondary adds protons, neutrons, Z, A and isotopes. The progression is natural.
Understanding atomic number Z is the key to reading the periodic table. This exam and the Periodic Table exam complement each other perfectly.
H₂O has 2 hydrogens and 1 oxygen: 3 atoms in total. Questions teach students to read chemical formulae before they appear in other exams.
"A Year 10 student who did not understand isotopes sees the ¹²C and ¹⁴C question: same number of protons (carbon), different number of neutrons. In that moment it clicks."
Tricks and techniques to master this topic faster:
Proton(+) and neutron(no charge) go in the nucleus. Electron(-) orbits outside. A mental image beats memorising.
Atomic number Z = number of protons = what defines the element. Mass number A = protons + neutrons.
To calculate neutrons: N = A − Z. If carbon has A=12 and Z=6, it has 6 neutrons.
Isotopes = same element (same Z), different A (different number of neutrons). Example: ¹²C and ¹⁴C are both carbon.
If you are studying Atoms & Molecules — Atomic Structure, these curriculum topics complement each other:
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