About this experiment
Inspect how one element forms a three-dimensional covalent network, layered sheets or a closed cage. Select atoms to count their displayed neighbours and separate local bonding from bulk structure.
Learning goals
- Compare threefold and fourfold carbon coordination.
- Identify covalent bonds within graphite layers and the absence of covalent interlayer links in this model.
- Distinguish bulk coordination from missing bonds at fragment boundaries.
How to use it
- 1Select an interior diamond atom and count its four covalent neighbours.
- 2Switch to graphite and rotate the stack to inspect the AB layer offset.
- 3Separate the layers without changing their internal covalent links.
- 4Inspect the fullerene cage and verify that every cage atom has three neighbours.
The model
Assumptions
- Ideal diamond and sheet C-C distances are 1.54 and 1.42 angstroms. Bulk densities follow these rounded geometric inputs.
- Finite fragments have incomplete boundary coordination and no hydrogen termination. Graphite separation is imposed; interlayer forces are not solved.
- The C60 cage is a regular truncated icosahedron. Real fullerene has inequivalent bond lengths; the model uses equal edges. A single sheet or isolated molecule has no defined bulk density here.
Try this in class
- Q1Why do exposed edge atoms have fewer neighbours than the bulk coordination number?
- Q2Why can graphite layers separate without breaking the in-plane covalent network?
Frequently asked questions
Does the model predict electrical conductivity or hardness?
No. It shows geometric bonding networks. Electronic transport, lattice dynamics and macroscopic mechanical failure are not calculated.
Why does widening graphite spacing reduce model bulk density?
The same mass occupies a larger repeated cell volume. The number and length of in-plane bonds remain unchanged.