‹ Chemistry simulationsChemistry · AS Level 9701 · 14 HydrocarbonsFive simulations covering Topic 14: the tetrahedral shape of alkanes and free rotation about a sigma bond, free radical substitution step by step, the pi bond of an alkene and why it cannot rotate, electrophilic addition with Markovnikov's rule, and the reactions of alkenes including addition polymerisation.
Every carbon in an alkane is surrounded by four single bonds pointing to the corners of a tetrahedron, and single bonds can rotate freely. The C–C and C–H bonds are strong and almost non-polar, which is why alkanes react with very little except oxygen and, in ultraviolet light, the halogens.
Methane and chlorine do nothing in the dark. In ultraviolet light they react by a chain reaction with three stages: initiation makes radicals, propagation uses one radical and makes another, and termination joins two radicals together. Step through it.
A double bond is one sigma bond plus one pi bond made by p orbitals overlapping sideways. The pi bond sits above and below the plane, holds the two carbons flat at 120°, and stops them twisting. Turn the pi bond on and off and try to rotate.
The pi bond is a region of high electron density, so it attacks anything electron-poor. With an unsymmetrical alkene there are two possible carbocations, and the reaction goes mostly through the more stable one. Step through the mechanism.
Everything an alkene does is an addition across the double bond. Pick a reagent to see the product and the conditions, or watch many monomers join into an addition polymer.
Alkanes in 3D with free rotation about a C-C sigma bond, free radical substitution stepped through initiation, propagation and termination, the alkene pi bond built from p orbitals with a twist slider that destroys the overlap, electrophilic addition with curly arrows and carbocation stability behind Markovnikov's rule, and the reactions of alkenes including addition polymerisation.
Five simulations covering Topic 14: the tetrahedral shape of alkanes and free rotation about a sigma bond, free radical substitution step by step, the pi bond of an alkene and why it cannot rotate, electrophilic addition with Markovnikov's rule, and the reactions of alkenes including addition polymerisation.
Hydrocarbons is a free, browser-based simulation for Cambridge International AS & A Level Chemistry 9701 (topic 14 Hydrocarbons). The same ideas are examined in Cambridge IGCSE Chemistry 0620 (topic 11 Organic chemistry). The course is assessed in Paper 1 (Multiple Choice (AS)), Paper 2 (AS Structured), Paper 3 (Advanced Practical), Paper 4 (A Level Structured), Paper 5 (Planning, Analysis, Evaluation). Syllabus for examination in 2025-2027. There are 5 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.
Full syllabus map: AS Level Chemistry 9701 topic 14.
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