Lecture 23 10/28/05

Quiz1. What does the quantum number “l” represent?

2. Calculate the wavelength of light emitted when an electron changes from n = 3 to n = 1 in the H atom?

m/s8100.3light speed of c

s J341062.6 h 1m7100974.1R

22

n

121

n

1R

λ

1

2initial

n

12final

n

1RhcΔE

2n

Rhcn

E mv

hλ

λ

hchνE λν c

ml orbital -l ... 0 ... +l

orientation

ml orbital -l ... 0 ... +l

orientation

Summary: Quantum numbers

n shell 1, 2, 3, 4, ... size and energy

l subshell 0, 1, 2, ... n – 1

shape

ms electron spin +1/2 and -1/2

spin

Pauli Exclusion Principle

No two electrons can have the same set of the four quantum numbers (n, l, ml, ms)

Writing Atomic Electron Configurations

Writing Atomic Electron Configurations

11 s

value of nvalue of l

no. ofelectrons

spdf notationfor H, atomic number = 1

Two ways of writing configurations

spdf notation

Two ways of writing configurations

spdf notation

Writing Atomic Electron Configurations

Writing Atomic Electron Configurations

Two ways of writing Two ways of writing configurationsconfigurations

orbital box notation.orbital box notation.

Two ways of writing Two ways of writing configurationsconfigurations

orbital box notation.orbital box notation. Arrowsdepictelectronspin

ORBITAL BOX NOTATIONfor He, atomic number = 2

1s

21 s

Arrowsdepictelectronspin

ORBITAL BOX NOTATIONfor He, atomic number = 2

1s

21 s

One electron has n = 1, l = 0, ml = 0, ms = + 1/2Other electron has n = 1, l = 0, ml = 0, ms = - 1/2

Aufbau principle Electrons are added from

lowest to highest energy

Single electron atom (Bohr) Energy related to n

Multi-electron atom Energy related to n + l

See “Toolbox” for Electron Configuration tool.See “Toolbox” for Electron Configuration tool.

LithiumLithiumLithiumLithium

Group 1A

Atomic number = 3

1s22s1 ---> 3 total electrons

1s

2s

3s3p

2p

BoronBoronBoronBoron

Group 3AGroup 3A

Atomic number = 5Atomic number = 5

1s1s2 2 2s2s2 2 2p2p11 ---> --->

5 total electrons5 total electrons

1s

2s

3s3p

2p

CarbonCarbonCarbonCarbonGroup 4AGroup 4A

Atomic number = 6Atomic number = 6

1s1s2 2 2s2s2 2 2p2p22 ---> --->

6 total electrons6 total electrons

HUND’S RULE When placing electrons in a set of orbitals having the same energy, fill each with a single electron first

1s

2s

3s3p

2p

OxygenOxygenOxygenOxygen

Group 6A

Atomic number = 8

1s2 2s2 2p4 --->

8 total electrons

1s

2s

3s3p

2p