Extension Of Molecular Orbitals to Other Atoms
The hydrogen atomic orbitals would not do us a great deal of good if orbitals of other atoms were radically different, since in that case different pictures would be required for each atom. But the feature of the hydrogen atom problem that determines the most important characteristics of the hydrogen atom orbitals is the spherical symmetry. Since all the atoms are spherically symmetric, the atomic orbitals of all atoms are similar, the main difference being in their radial dependence, that is, in how rapidly they approach zero as one moves away from the nucleus. Because the radial dependence is of minimal importance in qualitative applications, one may simply use orbitals of the shapes found for hydrogen to describe behavior of electrons in all the atoms.
Ground and Excited States
We know that an electron ina hydrogen atom in a stationary state will be described by one of the atomic orbital functions ?1s, ?2s,?2px and so forth. We can make this statement in a more abbriviated form by saying that the electron is in one of the orbitals ?1s, ?2s,?2px,…, and we use this more economical kind of statement.
The orbital that has associated with the lowest energy is ?1s if the electron is in this orbital, it has the lowest total energy possible, and we say that the atom is in its electronic ground state. If we were to give more energy, say enough to put it to ?2px orbital, the atom would be in an electronic excited state. In general, for any atom or molecule, the state in which all the electrons are in teh possible energy orbitals is the electronic ground state. Any higher energy state is called an electronic excited state.