Quantum Theory of Atoms

Quantum mechanics is a powerful method in modern physics for describing the motions and interactions of particles at small scales, such as the atoms. The ideas behind quantum mechanics often appear quite strange. Other physics topics, such as mechanics or optics, can be observed in the macroscopic physical world, but the microscopic world of quantum behavior is not easily grasped by the observer. An essential feature of quantum behavior is that it is generally impossible, even in principle, to measure a system without disturbing it. A great example of this behavior is the photoelectric effect. A major problem with Bohr's model was that it treated electrons as particles that existed in precisely-defined orbits. Based on de Broglie's idea that particles could exhibit wavelike behavior, Austrian physicist Erwin Schrödinger theorized that the behavior of electrons within atoms could be explained by treating them mathematically as matter waves. This model, which is the basis of the modern understanding of the atom, is known as the quantum mechanical or wave mechanical model.

Quantum numbers

Four quantum numbers are used to describe the movement and trajectories of each electron within an atom. Therefore, each electron in an atom has a unique set of quantum numbers. Quantum numbers designate specific shells, subshells, orbitals, and spins of electrons. In a matter of hierarchy, each shell consists of one or more subshells, and each subshell consists of one or more atomic orbitals.

Principal quantum number, n

The principal quantum number describes the most probable distance of the electrons from the nucleus, the larger the number n is, the further the electron is from the nucleus. The size of the orbital, affects the size of the atom. n can be any positive integer starting at 1. The value of n designates the principal electron shell.

Angular momentum quantum number, l

The orbital angular momentum quantum number determines the shape of an orbital. Each value of l indicates a specific subshell. The value of l is dependent on the principal quantum number. Unlike n, the value of l can be zero. It can also be a positive integer, but it cannot be larger than one less than the principal quantum number (n-1).

Magnetic quantum number

The magnetic quantum number determines the number of orbitals and their orientation within a subshell. Its value depends on the orbital angular momentum quantum number l.

Spin quantum number

The spin quantum number does not depend on another quantum number. It designates the direction of the electron spin and may have a spin of +1/2, represented by ↑, or –1/2, represented by ↓.