Electronic Structure of Atoms

The energy of electrons is quantized * Quantization: only specific values of energy are possible * Shells only occur at quantized energies * 3 important effects balance each other * Electrostatic attraction that draws then electrons toward the nucleus * Electrostatic repulsion between the electrons * The wavelike nature of an electron that prefers to be delocalized, spreading the electron density over a large volume space
Electron shells are identified by the quantum numbers 1,2,3,4,etc
Each shell can contain up to 2n^2 electrons * n=the number of the shell
Electrons in lower numbered shells are closest to the positively charged nucleus and are held most strongly by it * Lowest in energy
Electrons in higher numbered shells are furthest from the post charged nucleus and are held less strongly * Higher in energy
Shells are divided into subshells (spdf) * Within these sub shells, electrons are grouped into orbitals * Orbital: a region of space that can hold 2 electrons and has a specific quantized energy * Orthogonal: orbitals have no net overlap

Ground state electron configuration: electron configuration of lowest energy
Aufbau principle: orbitals fill in order of increasing energy, from lowest to highest * 1s, 2s, 2p, 3s, 3p, etc
Pauli exclusion principle: only 2 electrons can occupy an orbital and their spins must be paired * A given electron can exist in only two different spin states * 2 electrons with opposite spins are said to have paired spins
Hund’s rule: when orbitals of equal energy (called degenerate) are available but there aren’t enough electrons to fill all of them completely, one electron is added to each orbital before a second one is added to any of them; spins of the single electrons in the degenerate orbitals should be aligned * Partially filling orbitals as much as possible minimizes electrostatic repulsion between electrons
Energy level diagrams: pictorially designate where electrons are placed in an electron configuration * Moving up the diagram means higher energy * Electrons are drawn as arrows * Lines draw indicate relative energy

Energy: the ability to do work
The higher in energy an entity is, the more work it can perform
Excited state: a state of a system at higher energy than the ground state * Unstable in comparison to ground state
All of nature seeks its lowest energy state
When the electrons are rearranged back to the ground state, energy is released
Electrons in lower energy orbitals are held tightly to the nucleus * Would take a large amount of energy to remove these electrons * Ionization potential: the energy it takes to remove an electron from an atom or molecule * The closer the electron is to the nucleus, the greater the ionization potential