?total of four quantum numbers are used to describe completely the movement and trajectories of each electron?within an atom. The combination of all quantum numbers of all electrons in an atom is described by a wave function that complies with the?Schr?dinger equation.?Each electron in an atom has a unique set of quantum numbers; according to the?Pauli Exclusion Principle, no two electrons can share the same combination of four quantum numbers. Quantum numbers are important because they can be used to determine the electron configuration of an atom and the probable location of the atom's electrons. Quantum numbers are also used to determine other characteristics of atoms, such as ionization energy and the atomic radius.

The Four Electronic Quantum Numbers

Quantum numbers designate specific shells, subshells, orbitals, and spins of electrons. This means that they describe completely the characteristics of an electron in an atom, i.e., they describe each unique solution to the?Schr?dinger equation, or the wave function,?of electrons in an atom. There are a total of four quantum numbers: the principal quantum number (n), the orbital angular momentum quantum number (l), the magnetic quantum number (ml), and the electron spin quantum number (ms). The principal quantum number,?nn, describes the energy of an electron and the most probable distance of the electron from the nucleus. In other words, it refers to the size of the orbital and the energy level an electron is placed in. The number of subshells, or?ll, describes the shape of?the orbital. It can also be used to determine the number of angular nodes. The magnetic quantum number,?ml, describes the energy levels in a subshell, and?msrefers to the spin on the electron, which can either be up or down.

The Principal Quantum Number (nn)

The principal quantum number,?nn,?designates the principal electron shell. Because?n?describes the most probable distance of the electrons from the nucleus, the larger the number?n?is, the farther the electron is from the nucleus, the larger the size of the orbital, and the larger the atom is.?n?can be any positive integer starting at 1, as?n=1n=1?designates the first principal shell (the innermost shell). The first principal shell is also called the ground state, or lowest energy state. This explains why?nn?can not be 0 or any negative integer, because there exists no atoms with zero or a negative amount of energy levels/principal shells.?When an electron is in an excited state or it gains energy, it may jump to the second principle shell, where?n=2n=2. This is called absorption because the electron is "absorbing" photons, or energy. Known as emission, electrons can also "emit" energy as they jump to lower principle shells, where?n?decreases by whole numbers. As the energy of the electron increases, so does the principal quantum number, e.g.,?n?= 3 indicates the third principal shell,?n?= 4 indicates the fourth principal shell, and so on.

n=1,2,3,4?(1.1)