Chemistry Definitions Guide
Pauli's Exclusion Principle
No two electrons in an atom can have the same four quantum numbers
AufBau Principle
German word for "building up" is the guide for filling orbitals. In each successive atom added, it will occupy the lowest-energy orbital avaliable. As long as:
  1. Lower-energy orbitals fill before higher-energy
  2. An orbital can hold only two electrons, which must have opposite spins(an extension of Pauli's Principle)
  3. If two or more degenerate orbitals are available, one electron goes into each until all are half-full.
Hund's Rule
If two or more orbitals with the same energy are available, one electron goes in each until all are half full. The electrons in the half-filled orbitals all have the same value of their spin quantum number.
Oxidation Number
A value that measures whether an atom in a compound is neutral, electron-rich, or electron poor compared to an isolated atom
The loss of one or more electons by a substance
Oxidation-Reduction Reaction
A process in which one or more electrons are transferred between reaction partners
Oxidation Agent
A substance that causes an moxidation by accepting an electron
The gain of one or more electrons by a substance
Reducing Agent
A substance that causes a reduction by donating an electron
Valence Shell
The outermost electron shell
Octet Rule
The statement that main-group elements tend to undergo reactions that leave them with eight valence electrons
Lewis Structure
An electon-dot structure or representation of a molecule that shows valence electrons as a dot
Lattice Energy
The sum of the electrostatic interactions between ions in a solid that must be overcome to break a crystal in individual ions
Ionization Energy
(Ei) The amount of energy necessary to remove the outermost electron from an isolated neutral atom in the gaseous state
(EN) The ability of an atom in a molecule to attract the shared electrons in a covalent bond
Electron Affininty
(Eea) The energy change that occurs when an electron is added to an isolated atom in the gaseous state
Molecular Orbital Theory
A quantum mechanical description of bonding in which electrons occupy molecular orbitals that belong to the entire molecule rather than to an individual atom.
Quantum Number
A variable in solutions to the Schrodinger wave equation that describes the energy level and position in the space where an electron is most likely to be found
Principle Quantum Number(n)
A positive interger(n=1,2,3,4,...) on which the size and energy of the orbital primarilty depends. As n increases, the number of allowed orbitals increases and the size of the orbitals also increases.
Angular-Momentum Quantum Number(l)
Is the three-dimentional shape of the orbital. l is dependant on n, if n=1 then l=0, if n=2 then l=0 or 1, if n=3 then l=0,1,2...
Quantum Number l: 0 1 2 3 4
Subshell Notation s p d f g
Magenetic Quantum Number(ml)
The spatial orientation of the orbital with respect to a standard set of coordinate axes. For an orbital whose angular-momentum quantum number is l, the magnetic quantum number ml can have any intergral number value from -l to +l
Effective Nuclear Charge
The repulsion of outer-shell electrons by inner-shell electrions