Chapter 3.3

Electron Configuration

Compare the Rutherford, Bohr, and Quantum models of the atom.Rutherford’s model of atom

Electrons orbit the nucleus just as planets orbit the sun

Bohr’s model of the atomElectrons travel around the nucleus in specific

energy level

Quantum – difference in energy between

two energy levels.

Objective 1:

Bohr Video

Quantum model of the atomElectrons are found in orbitals around the

nucleus of atom.Orbital (electron cloud) – region of atom where

there is a high probability of finding electrons

Particles Cathode ray tubePhotoelectric effect

WavesElectromagnetic spectrumLine-emission spectrum

Electrons – Act like particles and waves

Electrons start in ground stateLowest possible energy level

Run electricity through gasElectrons absorb this energy

They move to excited stateElectron has more energy than normal

Quickly fall back to ground stateEnergy is emitted as light

Light has a specific wavelengthDetermines color (and line-emission

spectrum)

Light provides information about electrons Neon

Krypton

Argon

Objective 2:Explain how the wavelengths of light emitted by an atom provide information about energy levels.

Emission Spectrums

List the four quantum numbers, and describe their significance.

Quantum numbers:Number that specifies the properties of electrons

Tells where they are in the atom.

1. Principle quantum number ( n ) Main energy level n = 1,2,3,4,5 …….. Infinity

Distance from nucleus

2. Angular Momentum quantum number ( l ) indicates the shape of the orbital l = 0, 1, 2, 3 s p d f

Objective 3:

sp

d

3. Magnetic (m) • orientation of orbital around

nucleus

m =-2,-1,0,+1,+2

m =-1,0,+1

m = 0

4. Spin Quantum Number ( +1/2, -1/2) or ,

Indicates the two fundamental spin states of electron in an orbital

Single orbital can hold a maximum of 2 electrons

Quantum Numbers of the 1st thirty atomic orbitalsn l m Orbital

nameNumbe

r of Orbital

s

Number of

Electrons

1 0 0 1s 1 2

2 0 0 2s 1 2

2 1 -1,0,1 2p 3 6

3 0 0 3s 1 2

3 1 -1,0,1 3p 3 6

3 2 -2,-1,0,1,2 3d 5 10

4 0 0 4s 1 2

4 1 -1,0,1 4p 3 6

4 2 -2,-1,0,1,2 4d 5 10

4 3 -3,-2,-1,0,1,2,3 4f 7 14

2

8

18

32

Total Electrons in

n

Write the electron Configuration of an atom by using the Pauli Exclusion principle and the aufbau principle.

Objective 4

Electron ConfigurationThe arrangement of electrons in an atom

Lowest-energy arrangement – ground-state electron configuration

Rules Governing Electron Configuration1. Aufbau Principle – electron occupies the lowest-

energy orbital that can receive it. Pg. 105

2. Pauli exclusion Principle – no two electrons in the same atom can have the same set of four quantum numbers

3. Hund’s Rule – 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.

4f 5f 6f 7f

3d 4d 5d 6d 7d

2p 3p 4p 5p 6p 7p

1s 2s 3s 4s 5s 6s 7s

Aufbau principle

** Gives the order of energy levels and orbitals

Pauli Exclusion Principle

Hund’s Rule

Representing Electron Configurations

1. Orbital Notation

• Na __ __ __ __ __ __

1s 2s 2p 3s

2. Electron-Configuration Notation

• Na 1s22s22p63s1

3. Noble-Gas Notation

• Na [Ne] 3s1

1. Write the electron configuration, orbital notation, and noble gas notation for an atom whose atomic number is:

a) 20b) 8c) 17

Writing Electron Configuration