Chapter 5

Electrons in Atoms

Wave Nature of Light• Wavelength (λ) – shortest distance between

equivalent points on a continuous wave (unit: m or nm) • Ex: Crest to Crest or Trough to Trough

Wave Nature of Light• Frequency (ν) – the number of waves that pass a

given point per second (unit: Hz or 1/s)• 1 Hertz (Hz) = 1 wave per second

Electromagnetic Radiation• form of energy with wave-like behavior

Wavelength and Frequency Relationship:

Inverse Relationship: Long Wavelength mean Low Frequency

Speed of Light • ALL electromagnetic radiation moves at

the speed of light

• speed of light = c = 3.0 x 108 m/s

• Formula:

c = λν = (wavelength) x (frequency)

Sample Problem• Microwaves are used to cook food and transmit

information. What is the wavelength of a microwave that has a frequency of 3.44x109 Hz?

Given: ν = 3.44 x 109 Hz

Find: λ = ?

m/s 10 x 3.00 c 8

c c

Equation:

c

m1072.8

s110 3.44

sm 1000.3

2

9

8

Electromagnetic Spectrum • shows all forms of electromagnetic

radiation (pg 139)

Electromagnetic Spectrum • shows all forms of electromagnetic

radiation (pg 139)

Emission Spectrum

• Ground State: lowest, most stable energy state of an electron

• Excited State: has more energy than the ground state

• Photon: particle of electromagnetic radiation

• Light is both a particle and a wave

Photon

• Every element has its own specific atomic emission spectrum

• When an excited electron returns to the ground state, it gives off a photon of electromagnetic radiation.

• Electrons are located in the electron cloud.

• The electron does not have a definite path nor can it be specifically located, but we can predict its whereabouts based on probabilities called orbitals

Quantum Theory and Numbers

• gives an electron’s position in an atom

• 4 quantum numbers• n• l• m• s

Quantum NumbersName Symbol Definition Details

n

l

m

s

Indicates the orientation in

space (dependent on

the shape)

Subshell indicates the shape of the

orbital

Indicates the average

distance of the electron from the nucleus

Indicates the direction of spin of the electron

n is the period number (a

number between 1 and

7)Shapes are labeled by

letters (s,p,d,f)

s = 1 orientationp = 3 orientationsd = 5 orientationsf = 7 orientationsSpin is either +1/2 or -1/2

Orbital QN

Magnetic QN

Spin QN

Principle QN

If we compared Quantum Numbers to an address then

state

city

street

Side of street

Important note:

EVERY electron in an atom has a specific,

unique set of the four quantum numbers!

n (Principle Quantum #)• Discovered and presented by Niels

Bohr in the Bohr model of the atom

• Indicates:• The distance from the nucleus• The size/volume of the electron’s orbital• The atom’s major energy levels

• The further the electron is from the nucleus the greater n will be

n (Principle Quantum #)

The larger the n the greater volume of the electron cloud and the greater the energy

n can be a number between 1 and 7

l (Orbital Quantum #)• Indicates the shape of the orbital (the

sub shell)

s p

d f

m (Magnetic Quantum #)The shape is determined by l but m determines how the shape is oriented in space.

s orbital – spherical Only 1 orientation

m (Magnetic Quantum #)The shape is determined by l but m determines how the shape is oriented in space.

p orbital: “dumbbell” 3 orientations

m (Magnetic Quantum #)The shape is determined by l but m determines how the shape is oriented in space.

d orbital: 5 orientations

m (Magnetic Quantum #)The shape is determined by l but m determines how the shape is oriented in space.

f orbital: 7 orientations

m (Magnetic Quantum #)Each orbital orientation can hold only 2 electrons:

s : 1 orientation = 2 total electrons p : 3 orientations = 6 total electronsd : 5 orientations = 10 total electronsf : 7 orientations = 14 total electrons

s (Spin Quantum Number)• Indicates which direction the

electron spins• The 2 electrons in an orbital

orientation will have opposite spins ( + ½ or – ½)

Pauli Exclusion PrincipleEach electron in an atom has a unique set of quantum number therefore, a maximum of two electrons can occupy a single

atomic orbital

Electron Configuration• Quantum numbers are used to write

electron configurations of an element

Hydrogen HAtomic number: 1

1s1n

Shape determined by l

# of electrons

Aufbau PrincipleEach electron occupies the

lowest energy orbital available

Two Methods of Writing Configurations

Write the configuration of Na:

1s2 2s2 2p63s1

Na has 11 electrons

The electrons from the configuration should add up to 11.

Method 1

Remember: s can hold 2 electrons, p 6, d 10 and f 14

Two Methods of Writing Configurations

Use the periodic table

Write the electron configuration for Ar:

Ar

Always start at

1s

1s2 2s2 2p6 3s2 3p6

Argon’s atomic number is 18The superscripts from the electron configuration added equal 18.

Examples• Write the electron configuration for the following

elements:

C:

P:

Ag:

Rn:

1s22s22p63s23p3

1s22s22p2

1s22s22p63s23p64s23d104p65s24d9

1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6

Orbital Notation• Electron configurations can be

written as diagrams • Orbital Notation diagrams show the

individual orientations and the electrons that fill them.

• Hund’s Rule: fill orbitals so that the number of unpaired spins is maximized; electrons will fill orbitals before pairing up

Orbital Notation• Write the orbital notation for

Carbon:Electron configuration: 1s22s22p2

1. Write a line for each orientation associated with a orbital shape: s = 1, p = 3, d = 5, f = 7

2. Fill electrons in each shape. Place a single electron in each orbital before pairing them up.

1s 2s 2p

Examples• Write the orbital notation for the following

elements:

C:

P:

Ag:

Rn:

Noble Gas ConfigurationAll electron configurations can be

abbreviated…

Electron Configuration for Ca is:

Noble gas configuration for Ca is:

Lewis Dot Diagrams• The outer electrons are use to draw

Lewis Dot Diagrams

• The number of electrons in the highest principle quantum number (largest “n” values) determines the number of electrons in the diagram

ExamplesH 1s1

Be 1s22s2

N 1s22s22p3

Ne 1s22s22p6

5 electrons

2 electrons

1 electron

8 electrons

Ne ::

::

H .

N

:

. ..

Be

.

.