‹ All simulationsChemistry · AS Level 9701 · 1 Atomic structureEight simulations covering the whole of Topic 1: particles and the nucleus (1.1, 1.2) and electron energy levels (1.3). Rotate the 3D scenes with drag, zoom with the wheel or pinch. Everything updates live as you change the controls.
Add or remove protons, neutrons and electrons and watch the identity of the atom change. Electrons fill shells on the 2, 8, 8, 2 pattern used for Bohr diagrams up to calcium.
A mass spectrum is a bar chart of isotope abundance. Drag the abundance sliders and the weighted mean, the relative atomic mass, recalculates in real time.
The regions where an electron is most likely to be found. Rotate each orbital to see its true geometry. Lobe colours show the two phases of the wavefunction (+ and −), which is why p and d orbitals point in specific directions.
Fill subshells one electron at a time in order of increasing energy. Watch 4s fill before 3d, and see electrons pair only after each orbital in a subshell has one (Hund's rule). Arrows show electron spin.
Strip electrons off one at a time. Each removal is plotted as log(ionisation energy). The big jumps in the graph line up with the moment you break into a new, inner shell, which is the evidence for shell structure.
Click any element to see why its first ionisation energy sits where it does, using the three competing factors: nuclear charge, shielding and distance, and spin-pair repulsion. The two dips (group 2 to 13, group 15 to 16) are the whole reason this topic is worth teaching carefully.
Fire protons, neutrons and electrons at the same speed between two charged plates. Neutrons pass straight through, protons bend toward the negative plate, and electrons bend the opposite way and far more sharply because their mass is tiny. This is the syllabus experiment for showing charge and mass.
Compare sizes directly. Atoms shrink across a period as nuclear charge pulls the same shell in tighter, and grow down a group as shells are added. Positive ions are smaller than their atom, negative ions are larger. Spheres are drawn to scale with each other.