Electrons in Electrons in Atoms NotesAtoms Notes

Electron ConfigurationsElectron Configurations

Quantum modelQuantum model

Electron ConfigurationsElectron Configurations

the arrangement of electrons in an the arrangement of electrons in an atomatom

each type of atom has a unique each type of atom has a unique electron configurationelectron configuration

electrons tend to assume positions that electrons tend to assume positions that create the lowest possible energy for create the lowest possible energy for atom atom

ground state electron configuration- ground state electron configuration- lowest energy arrangement of lowest energy arrangement of electronselectrons

Rules for ArrangementsRules for Arrangements

Aufbau Principle-Aufbau Principle- an an electron occupies the electron occupies the lowest-energy orbital lowest-energy orbital that can receive itthat can receive it

Beginning in the 3Beginning in the 3rdrd energy level, the energy level, the energies of the energies of the sublevels in different sublevels in different energy levels begin energy levels begin to overlapto overlap

Rules for ArrangementsRules for Arrangements

Pauli Exclusion Principle-Pauli Exclusion Principle- no two no two electrons in the same atom can have electrons in the same atom can have the same set of 4 quantum numbersthe same set of 4 quantum numbers

Hund’s Rule-Hund’s Rule- orbitals of equal orbitals of equal energy are each occupied by one energy are each occupied by one electron before any orbital is electron before any orbital is occupied by a secondoccupied by a second

all unpaired electrons must have the all unpaired electrons must have the same spinsame spin

Rules for ArrangementsRules for Arrangements

Writing Writing Configurations Configurations

Orbital Notation:Orbital Notation: an orbital is written as a linean orbital is written as a line each orbital has a name written below iteach orbital has a name written below it electrons are drawn as arrows (up and electrons are drawn as arrows (up and

down)down) Electron Configuration NotationElectron Configuration Notation

number of electrons in sublevel is number of electrons in sublevel is added as a superscriptadded as a superscript

Order for Filling on the Order for Filling on the Periodic TablePeriodic Table

S p d f sublevel orbitalsS p d f sublevel orbitals- shape is based on the probability - shape is based on the probability of an electron to be somewhere at of an electron to be somewhere at any given timeany given time

Writing ConfigurationsWriting Configurations Start by finding the number of electrons Start by finding the number of electrons

in the atomin the atom Identify the sublevel that the last electron Identify the sublevel that the last electron

added is in by looking at the location in added is in by looking at the location in periodic tableperiodic table

Draw out lines for each orbital beginning Draw out lines for each orbital beginning with 1s and ending with the sublevel with 1s and ending with the sublevel identifiedidentified

Add arrows individually to the orbitals Add arrows individually to the orbitals until all electrons have been drawnuntil all electrons have been drawn

Silicon Silicon number of electrons: 14number of electrons: 14 last electron is in sublevel: 3plast electron is in sublevel: 3p

1s 2s 2p 3s 3p

Valence Electrons- the electrons in the outermost energy level

ChlorineChlorine number of electrons: 17number of electrons: 17 last electron is in sublevel: 3plast electron is in sublevel: 3p

2p 3s 3p 1s 2s

SodiumSodium

number of electrons: 11number of electrons: 11 last electron is in sublevel: 3slast electron is in sublevel: 3s

1s1s22 2s 2s22 2p 2p66 3s3s11

1s 2s 2p 3s

CalciumCalcium

number of electrons: 20number of electrons: 20 last electron is in sublevel: 4slast electron is in sublevel: 4s

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22

1s 2s 2p 3s

3p 4s

BromineBromine

number of electrons: 35number of electrons: 35 last electron is in sublevel: 4plast electron is in sublevel: 4p

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s2 2 3d3d1010 4p 4p55

1s 2s 2p 3s 3p

4s 3d 4p

1s 2s 2p 3s 3p

4s 3d 4p

ArgonArgon

number of electrons: 18number of electrons: 18 last electron is in sublevel: 3plast electron is in sublevel: 3p

1s1s22 2s 2s22 2p 2p66 3s3s22 3p 3p66

1s 2s 2p 3s 3p

Noble Gas NotationNoble Gas Notation

short hand for larger atomsshort hand for larger atoms configuration for the last noble gas is configuration for the last noble gas is

abbreviated by the noble gas’s symbol in abbreviated by the noble gas’s symbol in bracketsbrackets