Electron Configurations Chapter 4 Chm 1.1.3

Where are the e- in an atom? Electron cloud model – probability of finding electrons Atoms are separated into Energy Levels (n) (1, 2, 3, 4…etc) Sublevels (s, p, d and f) Orbital's (s = 1, p = 3, d= 5, f = 10)

Energy Level = n Corresponds to the period (row) the element is in Ex: H = period 1 = 1 energy level C = period 2 = 2 energy levels Al = period 3 = 3 energy levels

Sublevel (s, p, d or f) Corresponds to the “block” the element is in S

Orbitals An orientation (shape) Each orbital can hold 2 electrons Each sublevel can have a certain number of sublevels s = 1 2 e- p = 3 (px, py, pz) 6 e- d = 5 10 e- f = 7 14 e-

Principles Pauli Exclusion Principle – no two electrons can have the same location in the electron Aufbau Principle – energy levels must be full for e- to go into a higher one Hunds Rule – electron must fill orbitals one at a time before pairing

Electron Configurations Hydrogen * period 1 = 1 energy level * block s = electron is in sublevel s * orbital = s has 1 orbital * electron = H has 1 1s ___

Helium * period 1 = 1 energy level * block s = electrons are in sublevel s * orbital = s has 1 orbital * electrons = He has 2 1s ____

Lithium * period 2 – has 2 energy levels (1 and 2) * block s = highest e- is in s sublevel * orbital = s has 1 orbital * electrons = lithium has 3 1s ___ 2s ___

Boron * period 2 = 2 energy levels (1 and 2) * block p = highest electrons are in sublevel p * orbital = p has 3 orbitals * electrons = there are 5 1s ___ 2s ___ 2p ___ ___ ___

Fluorine * period 2 = 2 energy levels (1 and 2) * block p = highest electrons are in p sublevel * orbital = p has 3 orbitals * electrons – F has 9 1s ___ 2s ___ 2p ___ ____ ____

Every element’s atoms are just like the one before it just with Remember ….. Every element’s atoms are just like the one before it just with 1 more electron!

Energy Level Sequence Goes in order until you get through 3p 3d is expected next but…. 4s has lower energy than 3d (d block is always one less than the period) e- want to be in LOWEST ENERGY state Sequence is thrown off after 6s too 4f comes next (f block is always 2 less)

Electron Configurations Orbital notation – orbital's shown, arrows used for electrons Electron Configuration – only energy level, sublevel and total number of e- are shown Noble Gas Notation – noble gas symbol in brackets in substituted for lengthy electron configuration