Quantum Numbers

Electrons in Motion Electrons are the only subatomic particles that are in constant motion. Study of the motion of electrons is called Quantum Mechanics. Because of this, scientists have created an “address” system to help determine where an electron is most likely to be found in the electron cloud. Quantum numbers give the “address” for an electron orbiting the nucleus

4 Quantum Numbers There are 4 quantum numbers which tell the most likely location of an electron in a specific space around the nucleus. n : energy level l : sublevel m : orbital s : spin of electron We will look at each quantum number individually.

n stands for Energy Level Energy level is the distance an electron is from the nucleus. The smaller the energy level, the closer to the nucleus an electron is.

l stands for Sublevel Each energy level is broken down into sublevels s,p,d,f Each sublevel has a corresponding number: s = 0 p = 1 d = 2 f = 3

m stands for Orbital Each sublevel is broken down into orbitals which can hold a maximum of 2 electrons (Pauli Exclusion Principle) Each electron will fill an empty orbital first before pairing up. (Hund’s Rule) Electrons will fill orbitals with the lowest energy levels first (Afbau Principle)

Numbers Assigned to Orbitals -1 0 +1 -2 -1 0 +1 +2 -3 -2 -1 0 +1 +2 +3

s Stands for Spin of Electron If there is only 1 electron in the orbital, it will spin in a clockwise direction indicated by an up facing arrow ( ) and the number assigned will be +1/2 If there are 2 electrons in an orbital, the last electron added will spin in a counterclockwise direction indicated by a down facing arrow( ) and the number assigned will be -1/2

ELEMENT SYMBOL ELECTRON CONFIG. (SHORTCUT) N L M S (energy level) L (sublevel) M (orbital) S (spin) Aluminum Silicon Chlorine Bromine Nitrogen Potassium Tungsten Zinc Uranium Gold Iron tin strontium

ELEMENT SYMBOL ELECTRON CONFIG. (SHORTCUT) N L M S Aluminum Al (energy level) L (sublevel) M (orbital) S (spin) Aluminum Al [Ne] 3s2 3p1 3 1 -1 + ½ Silicon Si [Ne] 3s2 3p2 Chlorine Cl [Ne] 3s2 3p5 - ½ Bromine Br [Ar] 4s2 4p5 4 Nitrogen [He] 2s2 2p3 2 +1 Potassium K [Ar] 4s1 Tungsten W [Xe] 6s2 4f145d4 5 Zinc Zn [Ar] 4s2 3d10 +2 Uranium U [Rn] 7s2 6d1 5f3 Gold Au [Xe] 6s2 4f145d9 Iron Fe [Ar] 4s2 3d6 -2 tin Sn [Kr] 5s2 4d10 5p2 strontium Sr [Kr] 5s2