-the arrangement of electrons in an atom -a distinct configuration for each element -assume the arrangement with the lowest possible energies (ground-state electron configuration)

1. Aufbau Principle 2. Pauli Exclusion Principle 3. Hund’s Rule

-shows the order in which electrons occupy orbitals -states: an electron occupies the lowest-energy orbital that can receive it Ex: lowest energy orbital is ls; the H electron occupies this orbital -beginning with the 3 rd main energy level, the energies of the sublevels begin to overlap

-reflects the importance of the spin quantum number -states: no two electrons in the same atom can have the same set of four quantum numbers 1s orbital

-orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin Ex: p sublevel being filled 1.____ ____ ____ 2.____ ____ ____ 3.____ ____ ____ 4.____ ____ ____ It is unpaired electrons that cause an element to be magnetic. Paramagnetism means weakly attracted due to unpaired electrons.

There are three methods, or notations, used to indicate electron configurations. They are: Orbital Notation Electron-Configuration Notation Noble-Gas Notation

-unoccupied level is ____ with orbital name underneath - ____ = orbital with 1 electron - ____ = orbital with 2 electrons, paired with opposite spins Ex: H ____ 1s He ____ 1s B ____ ____ ____ ____ ____ 1s 2s 2p x 2p y 2p z

-eliminates the lines and arrows of orbital notation -add superscript to sublevel designation Ex: H 1s 1 He 1s 2 B 1s 2 2s 2 2p 1

Electrons fill the areas which require the least amount of energy, and it takes less energy to fill the 4s than it does to fill the 3d. So, as soon as the 3p is filled the very next thing to begin to fill is the 4s, then the 3d fills and then the 4p. The orbits themselves are not overlapping – there is some overlapping of the energy of each of the orbits. To help us tell what will fill next, we will learn to use the Periodic Table.

-”s” and “p” electrons: main energy level # same as the period # -”d” electrons: main energy level # ONE LESS than the period # -”f” electrons: main energy level # TWO LESS than the period # -highest occupied level: the e- containing main energy level with the highest principal quantum number -inner shell electrons: electrons that are not in the highest occupied energy level -octet: “s” and “p” sublevels of highest energy level filled with 8 electrons

Noble Gases – the Group 18 elements (He, Ne, Ar, Kr, Xe, Rn) -use noble gas’s symbol in brackets to denote that much of the e- configuration, then add the remaining e- configuration Ex: Na = [Ne]3s 1 Noble Gas Configuration: an outer main energy level fully occupied, in most cases, by 8 e-

1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 7p 3d 4d 5d 6d 7d 4f 5f 6f 7f 5g 6g 7g Set up the s sublevels, then the p, d, and f. Follow the arrows in filling each successive orbital.