quantum number

A 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 Schrödinger equation. Each electron in an atom has a unique set of quantum numbers; according to the Pauli Exclusion Principle/Electronic Structure of Atoms and Molecules/Electronic Configurations/Pauli Exclusion Principle "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 understand other characteristics of atoms, such as ionization energy and the atomic radius. The value of the principal quantum number n is the level of the principal electronic shell (principal level). All orbitals that have the same n value are in the same principal level. For example, all orbitals on the second principal level have a principal quantum number of n=2. When the value of n is higher, the number of principal electronic shells is greater. This causes a greater distance between the farthest electron and the nucleus. As a result, the size of the atom and its atomic radius/Physical Properties of Matter/Atomic and Molecular Properties/Atomic Radii " increases. Because the atomic radius increases, the electrons are farther from the nucleus. Thus it is easier for the atom to expel an electron because the nucleus does not have as strong a pull on it, and the ionization energy/Physical Properties of Matter/Atomic and Molecular Properties/Ionization Energy " decreases. The orbital with n=2, because the closer the electron is to the nucleus or the smaller the atomic radius, the more energy it takes to expel an electron. To identify what type of possible subshells n has, these subshells have been assigned letter names. The value of l determines the name of the subshell: Another helpful visual in looking at the possible orbitals and subshells with a set of quantum numbers would be the electron orbital diagram. (For more electron orbital diagrams, see Electron Configurations/Electronic Structure of Atoms and Molecules/Electronic Configurations "Inorganic Chemistry/Electronic Configurations") .) The characteristics of each quantum number are depicted in different areas of this diagram. Pauli Exclusion Principle/Electronic Structure of Atoms and Molecules/Electronic Configurations/Pauli Exclusion Principle "Pauli Exclusion Principle") : In 1926, Wolfgang Pauli discovered that a set of quantum numbers is specific to a certain electron. That is, no two electrons can have the same values for n, l, ml, and ms. Although the first three quantum numbers identify a specific orbital and may have the same values, the fourth is significant and must have opposite spins. Hund's Rule/Electronic Structure of Atoms and Molecules/Electronic Configurations/Hund's Rules "Hund's Rules") : Orbitals may have identical energy levels when they are of the same principal shell. These orbitals are called degenerate, or "equal energy." According to Hund's Rule, electrons fill orbitals one at a time. This means that when drawing electron configurations using the model with the arrows, you must fill each shell with one electron each before starting to pair them up. Remember that the charge of an electron is negative and electrons repel each other. Electrons will try to create distance between it and other electrons by staying unpaired. This further explains why the spins of electrons in an orbital are opposite (i.e. +1/2 and -1/2). Heisenberg Uncertainty Principle/Quantum Mechanics/02. Fundamental Concepts of Quantum Mechanics/Heisenberg's Uncertainty Principle "Heisenberg's Uncertainty Principle") : According to the Heisenberg Uncertainty Principle, we cannot precisely measure the momentum and positi