Atomic Structure Electron Configurations

the arrangement of electrons in an atom each element has a unique electron configuration electrons fill the lowest energy levels first ground state electron configuration- lowest energy arrangement of electrons

Rules for Arrangements Aufbau Principle- an electron occupies the lowest-energy orbital that can receive it Beginning in the 3 rd energy level, the energies of the sublevels begin to overlap

Rules for Arrangements Pauli Exclusion Principle- no two electrons in the same atom can occupy the same place at the same time Hund’s Rule- orbitals of a sublevel are each occupied by one electron before any orbital is occupied by a second and all unpaired electrons must have the same spin

Rules for Arrangements

Writing Configurations Orbital Notation: –an orbital is written as a line –each orbital has a name written below it –electrons are drawn as arrows (up and down) Electron Configuration Notation –number of electrons in sublevel is added as a superscript

Order for Filling Sublevels

Writing Configurations How many e- in the atom? What sublevel (s,p,d,f) is the element in? Draw out lines for each orbital beginning with 1s and ending with the sublevel identified Add arrows individually to the orbitals until all electrons have been drawn

Silicon number of electrons: 14 last electron is in sublevel: 3p 1s 2s 2p 3s 3p  Valence Electrons- the electrons in the outermost energy level

Chlorine number of electrons: 17 last electron is in sublevel: 3p 2p 3s 3p 1s 2s

Sodium number of electrons: 11 last electron is in sublevel: 3s 1s 2 2s 2 2p 6 3s 1 1s 2s 2p3s

Calcium number of electrons: 20 last electron is in sublevel: 4s 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2s 2p3s 3p 4s

Argon number of electrons: 18 last electron is in sublevel: 3p 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2s 2p 3s3p

Bromine number of electrons: 35 last electron is in sublevel: 4p 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 1s 2s 2p 3s3p 4s3d 4p 1s 2s 2p 3s3p 4s3d 4p

Noble Gas Notation short hand for larger atoms configuration for the last noble gas is abbreviated by the noble gas’s symbol in brackets