Basic Electronic Structure of Atoms This page explores how you write electronic structures for atoms using s, p, and d notation. It assumes that you know about simple atomic orbitals - at least as far as the way they are named, and their relative energies. Case Study: Electron Configuration of Mn vs. Cu d-orbital Occupation and Electronic Configurations Electronic Configurations Intro The electron configuration of an atom is the representation of the arrangement of electrons distributed among the orbital shells and subshells. Commonly, the electron configuration is used to describe the orbitals of an atom in its ground state, but it can also be used to represent an atom that has ionized into a cation or anion by compensating with the loss of or gain of electrons in their subsequent orbitals. Many of the physical and chemical properties of elements can be correlated to electro Electronic Structure and Orbitals Hund's Rules Hund's rule states that: Every orbital in a sublevel is singly occupied before any orbital is doubly occupied. All of the electrons in singly occupied orbitals have the same spin (to maximize total spin). When assigning electrons to orbitals, an electron first seeks to fill all the orbitals with similar energy (also referred to as degenerate orbitals) before pairing with another electron in a half-filled orbital. Atoms at ground states tend to have as many unpaired electrons as possible. Pauli Exclusion Principle The Pauli Exclusion Principle states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins. This means if one is assigned an up-spin ( +1/2), the other must be down-spin (-1/2). Spin Pairing Energy Spin pairing energy refers to the energy associated with paired electrons sharing one orbital and its effect on the molecules surrounding it. Electron pairing determining the direction of spin depends on several laws founded by chemists over the years such as Hund's law, the Aufbau principle, and Pauli's exclusion principle. An overview of the different types laws associated with the electron pairing rules. Spin Quantum Number The Spin Quantum Number (s) is a value (of 1/2) that describes the angular momentum of an electron. An electron spins around an axis and has both angular momentum and orbital angular momentum. Because angular momentum is a vector, the Spin Quantum Number (s) has both a magnitude (1/2) and direction (+ or -). This vector is called the magnetic spin quantum number (ms). The Aufbau Process The Aufbau model lets us take an atom and make predictions about its properties. All we need to know is how many protons it has (and how many electrons, which is the same as the number of protons for a neutral atom). We can predict the properties of the atom based on our vague idea of where its electrons are and, more importantly, the energy of those electrons. The Octet Rule The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds. The Order of Filling 3d and 4s Orbitals This page looks at some of the problems with the usual way of explaining the electronic structures of the d-block elements based on the order of filling of the d and s orbitals. The way that the order of filling of orbitals is normally taught gives an easy way of working out the electronic structures of elements. However, it does throw up problems when you come to explain various properties of the transition elements. Additional Resources Michigan State Virtual Textbook of Organic Chemistry Electron Configurations of Atoms MasterOrganicChemistry From General Chemistry to Organic The Atom Electrons and Orbitals Effective Nuclear Charge Carey 4 th Edition On-Line Activity Atoms, Electrons and Orbitals Khan Academy Elements and Atoms Introduction to the Atom Atomic Orbitals Orbitals and Electron Configurations Electron Configurations Electron Configurations Part 2 Valence Electrons Leah4Sci Sub-Atomic Particles and Atomic Structure Periodic Table and Trends Atomic Orbitals and Shapes Electron Configuration Part 1 Electron Configuration Part 2 Intro to Organic Chemistry 1 Intro to Organic Chemistry 2 Cliffs Notes Principles of Atomic Structure Slide Presentations Web Pages Electron Configurations Electron Configurations and Orbital Diagrams Visualizing Atomic Orbitals ** Very complete introduction to the electronic structure of atoms Atomic orbitals Videos Electron Configurations and Orbital Diagrams Atomic Orbital Video electron configuration video Tutorial Chemistry is Easy! Electron Configurations