**NOTE**

• You do NOT need to know slides 3-10 at all. Those are simply for your information

Chapter 5 - Electron StructureChapter 5 - Electron Structure

• According to the Bohr Model, electrons (e-) can only orbit the nucleus in specific, allowed pathways.

• They move toward and away from the nucleus by “steps” or discrete amounts of energy that are released or absorbed.

• e- farther from the nucleus have more energy. Those closer to the nucleus have less energy.

• Very similar to a ladder. Just as you cannot step on the air between the rungs, an electron cannot exist between the levels.

• Ground state: the lowest energy of an atom

• Excited state: higher potential energy state

• Energy absorbed e- moves to higher state

• Energy emitted e- moves to lower state

Higher excited state

Excited state

Ground state

Excited state

Ground state

EnergyEnergy

The Duality of LightThe Duality of Light

“Duality” means that there are two ways to represent light.

• Light can behave like a wave or like a particle.

Wave Particle

Light as a Wave• Wavelength (λ – “lambda”): the distance

between the peaks

• Frequency (ν – “nu”): number of waves that pass a given point in a specific amount of time

λ

Two - facedTwo - faced

• wavelength (λ) frequency (ν)

c = 3.00 x 108 m/secThe speed of light (c) is constant. So as one gets bigger…the other has to get smaller! • Because of this relationship: Longer wavelength → Lower frequency Shorter wavelength → Higher frequency

• In the visible spectrum, color is associated with different wavelengths (RROOYY GG. . BBIIVV)

Longer λ and lower ν : towards Red

Shorter λ and higher ν : towards Violet

Examples…students walking across front of room Marching Band turning a corner

•The relationship is: c = λ ν

c = 3.00 x 108 m/secc = λ ν

Each of the different areas along the electromagnetic spectrum follows this equation

The marching band example

• There is obviously a relationship between the frequency of light and its energy:

Ephoton = hν

• ν is the frequency of the light, and h = 6.626 x 10-34 J·s (Planck’s constant) Higher ν → Higher E (Violet) Lower ν → Lower E (Red)

• Spectroscopy – gives you information about the structure of the atom…in other words it tells you the ladder the electrons follow

• Like fingerprints to the atom…identifies the element

Hydrogen’s Line Emission Spectrum

Excited State

Ground State

Energy (Light)

Go back to previous slide…show only certain wavelengths make it through due to the ladder of energy levels

Turn this sideways and it looks like a ladder

Specific element gas (light)…shows only the electrons specific energy levels …it’s ladder

White light …would show the whole visible spectrum…not just the ladder…Look back two slides

Light as a Particle• Photoelectric Effect: e- are emitted from a

metal when light of a high enough frequency shines on the metal.

• Importance: e- were not emitted when a light’s frequency was below a certain point – regardless of how long the light was shone on the metal => Light as a Particle

• Quantum – a small bundle of energy

• Photon – a small bundle of energy of light with zero mass

Metal

Light Electrons

Modern Atomic TheoryModern Atomic Theory

• We know electrons (e-) are particles, but in 1924, French scientist Louis de Broglie propose that e- have a wave nature as well (investigation showed this to be true)

• In 1926, Erwin Schrödinger developed a wave equation for e- that described their energy values correctly :

Eψ(x) = [-(h2/8π2m)d2/dx2 + V(x)] ψ(x) (OUCH!!!! Don’t worry, you don’t need to know this equation!!!)

• In 1927, Werner Heisenberg developed his Uncertainty Principle – it is impossible to determine simultaneously both the position and velocity of an electron or any other particle

This all led to the modern quantum theory

1. Orbitals describe the three dimensional space that electrons occupy.

2. The location of an electron can only be described by probability. (ex. You in this classroom and your parents are looking for you.)

3. Orbitals give shape to the atom.

• These properties allow us to describe electrons in terms of their energy and position.

• Ahhh Yes….. Quantum Mechanics!

Modern Atomic TheoryModern Atomic Theory

OrbitalNot anOrbit

Quantum MechanicsQuantum Mechanics….Sounds Scary!!!!

Think of it this way…

It is the “address” of an electron

Did you ever mail a letter?• Where do you live? (4 things)

- State

- City

- Street Name

- House Number

• Electrons are identified the same way (4 things)…

- Principle (identified by n)

- Orbital (identified by l)

- Magnetic (identified by ml)

- Spin (identified by ms)

Kevin Lockard2528 South St.

Lansdale, PA 19446

Four Quantum Numbers1. Principle Quantum Number (n)

• Indicates the main energy level occupied by the e- (distance from the nucleus)

• Shell Number (1st shell is closest to nucleus, 2nd is further, and so on …)

• Values of n can only be positive integers (1, 2, 3, etc.)

2. Orbital Quantum Number • Indicates the shape of the orbital (actual 3D space

where the probability of finding e- is greatest)

• Sublevel of n

• Designated s, p, d, f

s

p

d

1 2 3

• s orbital

– Spherical shaped

– One orbital

– Holds two e-

• p orbital

– Peanut or dumbbell shaped

– Three orbitals

– Holds six e-

• d orbital

– Double peanut shaped

– Five orbitals

– Holds ten e-

• f orbital

– Flower shaped

– Seven orbitals

– Holds fourteen e-

3. Magnetic Quantum Number • Indicates the orientation of an orbital (the plane that

the orbital is in)

• p orbitals can have three different orientations, one along the x-axis, one along the y-axis, and one along the z-axis

4. Spin Quantum Number • Indicates the two spin states of an e- in an orbital

(only 2 e- in each orbital, and they spin in opposite directions)

• Represented by arrows

px py pz

Empty Half-Filled Filled

Electron Configurations – Quick addressLike you were giving your address out to a friendThese have numbers and letters)It will look like this….

1s22s22p63s23p63d10 etc…..

4 Quantum Numbers – Boxed Address

How do you write this address How do you write this address for the electron?for the electron?

…2 different ways…

There are a few rules that help us represent the arrangement of electrons in atoms

address (tells us the “route” the mailman takes)

• Aufbau (“building up”) principle: an electron occupies the lowest energy possible

• Hund’s rule: orbitals of equal energy are each occupied by one electron before accepting a second electron

• Pauli exclusion principle: no two electrons in the same atom will have the same set of quantum numbers (no two fans have the same seat)

e-

How do you write this address How do you write this address for the electron?for the electron?

…2 different ways…

What’s the route the “mailman” takes?

What’s the route the “mailman” takes?

To write electron configurations, you need to know:

1. Period # 1 – 7 (exception for d orbitals – 1 less)

2. Subshell letter (e.g. s, p, d, f…)

3. Atomic # is # of e- as an exponent

Electron Configurations – Quick addressElectron Configurations – Quick address

ss dd pp

ff

Example

Sulfur = 1s22s22p63s23p4