Absolutely Small, Chapter 12: The Hydrogen Molecule and the Covalent Bond

The hydrogen molecule is the simplest molecule. A molecule is composed of two or more atoms held together by ôbonds.ö The hydrogen atom is composed of just two atoms. The idea of molecular orbitals is introduced. It is shown in detail what holds two hydrogen atoms together to form the hydrogen molecule. Using simple molecular orbital energy level diagrams it is explained why two hydrogen atoms bond to from a hydrogen molecule, but two helium atoms do not bond, and, therefore, there is no helium molecule.