Recall:◦ Werner Heisenberg formulated the Uncertanity Principle

that states it is impossible for us to know an electron’s exact position (where it is) and momentum (where it is going)

◦ As a result, we cannot identify specific orbits that electrons travel in

◦ We can only identify regions of space within an atom where an electron is most likely to be found ORBITALS!

◦ Schrodinger’s complex math equation allows us to: Calculate the shape of the electron cloud Probability of finding the electron at distinct locations within

those clouds

Recap of Last Class

How do the Orbitals Fill Up with Electrons?

An Introduction to Electron Configurations

Complete the activity “Welcome to Atomos Apartments!” on page 208

Assigning an Electron’s Address Explore

We use electron configurations◦ The way electrons are arranged in atoms

There are rules to follow!◦ Aufbau principle

Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atom have been accounted for

“aufbau” German for ‘build up or construct’

Predicting Electron Locations

aufbau chart

1s

3s

2s 2p

3d3p

4s 4p 4d 4f

5s 5p 5d 5f

Pauli’s Exclusion Principle◦ An orbital can hold only two electrons

Predicting Electron Locations

Hund’s Rule◦ “Electrons must fill a sub-level such that each

orbital has a spin up electron before they are paired with spin down electrons”

A bus analogy:◦ If you enter a bus and don’t know anyone on it, you will

pick a seat that is completely empty rather than one that already has a person in it

Predicting Electron Locations

Electrons fill in order from lowest to highest energy The Pauli exclusion principle holds. An orbital can

hold only two electrons Two electrons in the same orbital must have opposite

signs (spins) You must know how many electrons can be held by

each orbital◦ 2 for s◦ 6 for p◦ 10 for d◦ 14 for f

Hund’s rule applies. The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons for a set of orbitals◦ By convention, all unpaired electrons are represented as

having parallel spins with the spin “up”

Orbital Diagrams and Electron Configurations

Just a thought…◦ How do you determine the number of electrons in

an element? Examples:

◦ Oxygen◦ Magnesium◦ Argon◦ Scandium

Electron Configuration Practice

Orbital Notation

Use the Noble Gas symbol to abbreviate or shorten the electron configuration◦ Krypton◦ Rubidium◦ Zirconium

Short-Hand Notation

How Can We “Locate” an Electron?

Use Quantum Numbers!

Each electron has a specific ‘address’ in the space around a nucleus

An electrons ‘address’ is given as a set of four quantum numbers

Each quantum number provides specific information on the electrons location

Quantum Numbers

Electron Configuration

state

town

street

house number

state (energy level) - quantum number n

town (sub-level) - quantum number l

street (orbital) - quantum number ml

house number (electron spin) - quantum number ms

Quantum Numbers

Same as Bohr’s n Integral values: 1, 2, 3, …. Indicates probable distance from the

nucleus◦ Higher numbers = greater distance from nucleus◦ Greater distance = less tightly bound = higher

energy

Principal Quantum Number (n)

Integral values from 0 to n - 1 for each principal quantum number n

Indicates the shape of the atomic orbitals

Table 7.1 Angular momentum quantum numbers and corresponding atomic orbital numbers

Angular Momentum Quantum Number (l)

Value of l 0 1 2 3 4

Letter used

s p d f g

Integral values from l to -l, including zero Relates to the orientation of the orbital in

space relative to the other orbitals◦ 3-D orientation of each orbital

Magnetic Quantum Number (ml)

Magnetic Quantum Number

An orbital can hold only two electrons, and they must have opposite spins◦ Spin can have two values, +1/2 and -1/2

Pauli Exclusion Principle (Wolfgang Pauli)◦ "In a given atom no two electrons can have the

same set of four quantum numbers"

Electron Spin Quantum Number (ms)

Complete the Closer on Page 206

Closer!

Begin homework on page 209 – FRONT AND BACK!

Homework