As shown in Tab. 2, T0=1.049×10 5 K, ΔE=403 kJ/mol. It is consistent with the reference data 432 kJ/mol. The second isothermal orbit, the 2s orbit in quantum theory, is worth discussing for other elements. As shown in Fig. , the 2s orbit should be a pseudo-isothermal orbit shared by four non-isothermal orbits, constituting a tetrahedron. The electrons spread on the tetrahedral vertexes' surface as widely as possible to constitute another isothermal surface. Hence, the hybridization of sp orbits is not necessary. Similarly, orbits of the 3s, 4s, etc., are pseudo-isothermal. Four non-isothermal orbits constitute a layer. The higher layers may accommodate more non-isothermal orbits due to the large surface area of the pseudo-isothermal orbits. Therefore, r1s is about 24 pm, and T1s is about 2.3×10 5 K.