# 6: The Hydrogen Atom

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The solution of the Schrödinger equation (wave equation) for the hydrogen atom uses the fact that the Coulomb potential produced by the nucleus is isotropic (it is radially symmetric in space and only depends on the distance to the nucleus). Although the resulting energy eigenfunctions (the orbitals) are not necessarily isotropic themselves, their dependence on the angular coordinates follows completely generally from this isotropy of the underlying potential: the eigenstates of the Hamiltonian (that is, the energy eigenstates) can be chosen as simultaneous eigenstates of the angular momentum operator. This corresponds to the fact that angular momentum is conserved in the orbital motion of the electron around the nucleus. Therefore, the energy eigenstates may be classified by two angular momentum quantum numbers, ℓ and m (both are integers). The angular momentum quantum number ℓ = 0, 1, 2, ... determines the magnitude of the angular momentum. The magnetic quantum number m = −ℓ, ..., +ℓ determines the projection of the angular momentum on the (arbitrarily chosen) z-axis.

- 6.1: The Schrödinger Equation for the Hydrogen Atom Can Be Solved Exactly
- The solution of the Schrödinger equation (wave equation) for the hydrogen atom uses the fact that the Coulomb potential produced by the nucleus is isotropic (it is radially symmetric in space and only depends on the distance to the nucleus). Although the resulting energy eigenfunctions (the orbitals) are not necessarily isotropic themselves, their dependence on the angular coordinates follows completely generally from this isotropy.

- 6.2: The Wavefunctions of a Rigid Rotator are Called Spherical Harmonics
- The solutions to the hydrogen atom Schrödinger equation are functions that are products of a spherical harmonic functions and a radial function.

- 6.3: The Three Components of Angular Momentum Cannot be Measured Simultaneously with Arbitrary Precision
- The angular momentum operator is one of several related operators analogous to classical angular momentum. The angular momentum operator plays a central role in the theory of atomic physics and other quantum problems involving rotational symmetry. Two orthogonal components of angular momentum (e.g., \(L_x\) and \(L_y\)) are complementary and cannot be simultaneously known or measured. It is, however, possible to simultaneously measure or specify \(L^2\) and any one component of \(L\).

- 6.4: Hydrogen Atomic Orbitals Depend upon Three Quantum Numbers
- In solving the Schrödinger equation of the hydrogen atom, we have encountered three quantum numbers. The quantum numbers are not independent; the choice of nn limits the choice of ll, which in turn limits the choice of mm. A fourth quantum number, ss, does not follow directly from solving the Schrödinger equation but is to do with spin (discussed later).

- 6.5: s Orbitals are Spherically Symmetric
- The hydrogen atom wavefunctions are called atomic orbitals. An atomic orbital is a function that describes one electron in an atom. The radial probability distribution is introduced in this section.

- 6.6: Orbital Angular Momentum and the p-orbitals
- The physical quantity known as angular momentum plays a dominant role in the understanding of the electronic structure of atoms.

- 6.7: The Helium Atom Cannot Be Solved Exactly
- The second element in the periodic table provides our first example of a quantum-mechanical problem which cannot be solved exactly. Nevertheless, as we will show, approximation methods applied to helium can give accurate solutions in perfect agreement with experimental results. In this sense, it can be concluded that quantum mechanics is correct for atoms more complicated than hydrogen. By contrast, the Bohr theory failed miserably in attempts to apply it beyond the hydrogen atom.

- 6.E: The Hydrogen Atom (Exercises)
- These are homework exercises to accompany the chapter.

*Thumbnail: Depiction of a hydrogen atom with size of central proton shown, and the atomic diameter shown as about twice the Bohr model radius (image not to scale). Image used with permission (Public Domain; Bensaccount).*