Graphene smaller amplitude and higher frequency. This phenomenon, named "membrane effect", was predicted by Lifshitz in 1952. A prediction that was published in 2015 suggested a melting point of ≈4125 K. Recent and more sophisticated modelling has increased this temperature to at least 5000 K. At 6000 K (the sun's surface having an effective temperature of 5,777 K) graphene melts into an agglomeration of loosely coupled doubled bonded chains, before becoming a gas. The carbon–carbon bond length in graphene is about 0.142 nanometers. Graphene sheets stack to form graphite with an interplanar spacing of . Graphene is the strongest material ever
Vector model of the atom considered the extension of the Bohr model because Niels Bohr also proposed angular momentum was quantized according to: where "m" is an integer, produced correct results for the Hydrogen atom. Although the Bohr model doesn't apply to multi-electron atoms, it was the first successful quantization of angular momentum applied to the atom, preceding the vector model of the atom. For one-electron atoms (i.e. hydrogen), there is only one set of cones for the orbiting electron. For multi-electron atoms, there are many states, due to the increasing number of electrons. The angular momenta of all electrons in the atom add vectorially.