We have drawn three-dimensional contour plots of H-2(+) molecular orbitals and carbon hybrid orbitals according to explanations given in quantum chemistry textbooks and have also performed ab initio molecular orbital calculations of LiH and HF. Some contour representations and molecular orbital energy-level diagrams thus obtained are not consistent with the figures adopted in the textbooks. It is considered that the usual explanations for the molecular orbitals of H-2(+), LiH, HF, and hybridization in the conventional textbooks are liable to misunderstanding.