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### Chapter 5

### Important note:

### Pauli Exclusion Principle

### Aufbau Principle

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 = ?

Equation:

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 definitepath 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

If we compared Quantum Numbers to an address then

Quantum NumbersIndicates the average distance of the electron from the nucleus

n is the period number (a number between 1 and 7)

n

Principle QN

state

Subshell indicates the shape of the orbital

Shapes are labeled by letters (s,p,d,f)

l

Orbital QN

city

Indicates the orientation in space (dependent on the shape)

s = 1 orientation

p = 3 orientations

d = 5 orientations

f = 7 orientations

m

Magnetic QN

street

Indicates the direction of spin of the electron

Spin is either +1/2 or -1/2

s

Spin QN

Side of street

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

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 electrons

d : 5 orientations = 10 total electrons

f : 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)

Each electron in an atom has a unique set of quantum numbertherefore, 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 H

Atomic number: 1

1s1

n

# of electrons

Shape determined by l

Each electron occupies the lowestenergy orbital available

Two Methods of Writing Configurations

Method 1

Write the configuration of Na:

1s2

2s2

2p6

3s1

Na has 11 electrons

The electrons from the configuration should add up to 11.

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

Two Methods of Writing Configurations

Use the periodic table

Always start at 1s

Ar

Argon’s atomic number is 18

The superscripts from the electron configuration added equal 18.

Write the electron configuration for Ar:

1s2

2s2

2p6

3s2

3p6

Examples

- Write the electron configuration for the following elements:

C:

P:

Ag:

Rn:

1s22s22p2

1s22s22p63s23p3

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

Noble Gas Configuration

All 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

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