Electron Orbitals and Electron Configurations

Part II (a)

From orbits to orbitals!

We are going to move from Bohr’s model into the Quantum model of the atom

We are moving closer to our current understanding of where electrons are located in the atom

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Electron Cloud or OrbitalsElectron Cloud or Orbitals

Erwin SchrErwin Schrödinger used mathematics ödinger used mathematics to predict to predict probabilityprobability of finding an of finding an electron at a certain location in the electron at a certain location in the atomatomHe call the area of probability the electron cloud = the volume around the nucleus of an atom where its electrons are most likely found– I

Electron Cloud or OrbitalsElectron Cloud or Orbitals

We can’t be absolutely certain where any electron is at any time– But based on what science knows

presently, this is our very best guess

OrbitalOrbital = a region with a very high = a region with a very high probability of probability of finding finding the electron when the electron when it has a particular amount of energyit has a particular amount of energy

Electron Cloud or OrbitalsElectron Cloud or Orbitals

Think of the energy levels as the rungs on the ladder of the electron cloudJust like we can only stand on the rungs of a ladder and not between the rungs, the electron can be located only in certain energy levels within the atom– Lower energy levels are smaller and

located closer to the nucleus of the atom– Higher energy levels are larger and located

farther away from the nucleus

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The Quantum-Mechanical ModelThe Quantum-Mechanical Model

Each Each energy level (or shell) energy level (or shell) contain the contain the same numbersame number of of subshells subshells or sublevels or sublevels as the energy levelas the energy level

The The subshellssubshells are represented as a are represented as a letterletter

– s, p, d, fs, p, d, f

Each subshell has Each subshell has orbitalsorbitals with a with a particular shape.particular shape.

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Shells & SubshellsShells & Subshells

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The Quantum-The Quantum-Mechanical ModelMechanical Model

Energy Level # of subshells Orbital shape

1 1 s

2 2 s and p

3 3 s, p, and d

Apartment Complex Analogy

Think of an atom like an apartment complex

The energy level or shell is the floor

The subshells are the type of apartment– s = suite d = deluxe– p = penthouse f = flat

The orbitals have different occupancies based on their shape

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Probability Maps & Orbital ShapeProbability Maps & Orbital Shapess orbitalsorbitals are spherical and are spherical and

have 1 orbitalhave 1 orbital

1111

Probability Maps & Orbital ShapeProbability Maps & Orbital Shapepp orbitalsorbitals look like dumb bells and look like dumb bells and

have 3 orbitalshave 3 orbitals

Probability Maps & Orbital Shape Probability Maps & Orbital Shape dd orbitals orbitals have 5 orbitalshave 5 orbitals

Probability Maps & Orbital ShapeProbability Maps & Orbital Shapef Orbitals have 7 orbitals

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Atomic Orbitals

Watch the video (14:28)

http://www.youtube.com/watch?v=Ewf7RlVNBSA

Stop and answer questions about Atomic Orbitals

Electron Orbital Activity Lab

There are funny rules on how to fill the apartment complex or atom

Work with a partner to complete the electron configuration lab, but be sure

to follow these rules…

Apartment Rules

Rule A:From the Bottom Up: Rooms must be filled from the ground floor up. Fill the one room on the first floor before starting to put new tenants on the second floor. Then fill the s room before the p rooms. At higher floors the order might change a bit.

Apartment Rules

Rule B:Singles First: the owner of the building

wants to have the tenants spread out as much as possible. For that reason singles are placed in rooms before couples. If couples must be placed into a room then all of the other rooms on that floor must already have a single in them.

Apartment Rules

Rule C:

Opposite Gender Only: When two people are placed in a room they must be of opposite genders. No men may room together and no women may room together. This is an arbitrary rule on the part of the owners: in a just world we wouldn’t have to follow it. But quantum mechanics has nothing to do with justice.

Ions

Ions are atoms that have either lost or gained electrons

Remember electrons are negative, so how many protons and how many electrons would Cl -1 have?

Electron Lab

Now work with a partner to complete the Electron Orbital Activity Lab

What did we learn from the Lab?

Bohr part II (b)

Rule A: The Aufbau Principle 

• Place electrons in the energy shells and orbitals in order of energy, from low energy to higher energy

– i.e. Electrons are Lazy!

– s → p → d → f

• All orbitals related to an energy level are of equal energy.

– i.e. The three 2p orbitals are the same energy level.

Rule B: Hund’s Rule 

• When filling orbitals that have the same energy, place one electron in each before completing pairs

– i.e. Electrons are unfriendly! • Why? Electrons, being unfriendly, fill up

the empty orbitals before sharing orbitals. This is similar to seats on a bus – on a bus, you sit alone, rather than with a stranger, if there is an option.

Rule C: Pauli Exclusion Principle

A maximum of two electrons may occupy a single orbital, but only if the electrons have opposite spins.

– Spin -- Electrons have an associated “spin,” either one way or the other, like a top.

– These spins are called “spin up” and “spin down.”  

Big take aways from the Lab

Exceptions to filling order are copper, chromium and some others

Most stable are completely filled shells

Next most stable are half-filled shells

An atom may borrow an electron from next s shell to half fill a lower energy level.

Take aways from the Lab

Did you notice something funny about the order of the energy levels or orbitals?

Energy levels Energy levels don’t don’t always go in always go in order!order!

Relative Energy Levels

Take aways from the Lab

Occupanies: Did you notice how many electrons could occupy each type of room?

Suites (s orbitals) could hold 2

Penthouse (p orbitals) could hold 6

Deluxe (d orbitals) could hold 10

Flats (f orbitals) could hold 14

Orbital Occupancies

Subshell Name Number of Orbitals

Max number of electrons

s- subshell 1 (sphere) 1 X 2 = 2

p – subshells 3 (dumbbells) 3 x 2 = 6

d – subshells 5 5 x 2 = 10

f – subshells 7 7 x 2 = 14

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Writing electron configurations

Electron configurationElectron configuration = = distribution of electrons into the distribution of electrons into the various energy shells and various energy shells and subshells in an atom in its subshells in an atom in its ground ground statestate

Electron Configurations

Electron configuration is address information for electrons

The most stable arrangement is called the ground-state electron configuration.

This is the configuration where all of the electrons in an atom reside in the lowest energy levels possible.

Electron Configurations

2p4

Energy LevelEnergy LevelSubshellSubshell

Number of Number of electrons in electrons in the subshellthe subshell

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22 3d 3d1010 4p 4p66 5s 5s22 4d 4d1010 5p 5p66 6s6s22 4f 4f1414…… etc.etc.

Tro's Introductory Chemistry, Chapter 9Tro's Introductory Chemistry, Chapter 9 3333

Electron ConfigurationsElectron Configurations

Nitrogen:Nitrogen: 1s 1s222s2s222p2p33

(atomic number = 7)(atomic number = 7)

energy levelenergy level orbitalorbital

how many electronsin that orbital

What about ions?

What did you notice about ions?

When writing electron configuration for ions (when an element loses or gains electrons to become more stable), do it exactly the same way for the ion’s number of electrons

Writing Electron Configurations

Wouldn’t it be nice if we could write electron configuration without doing the orbital diagrams?

Well, we can! But we need to be careful because the energy levels do not always go in order!

We can use the diagonal rule to help us!

Diagonal Ruless

s 3p 3ds 3p 3d

s 2ps 2p

s 4p 4d 4fs 4p 4d 4f

s 5p 5d 5f 5g?s 5p 5d 5f 5g?

s 6p 6d 6f 6g? 6h?s 6p 6d 6f 6g? 6h?

s 7p 7d 7f 7g? 7h? 7i?s 7p 7d 7f 7g? 7h? 7i?

11

22

33

44

55

66

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By this point, we are past By this point, we are past the current periodic table the current periodic table so we can stop.so we can stop.

Writing Electron Configurations

Steps for the diagonal rule:Steps for the diagonal rule:Write the energy levels Write the energy levels top to bottomtop to bottom..Write the orbitals in s, p, d, f order. Write the orbitals in s, p, d, f order. Write the same number of orbitals as Write the same number of orbitals as the energy level.the energy level.Draw Draw diagonal linesdiagonal lines from the top right from the top right to the bottom left.to the bottom left.To get the correct order, To get the correct order, follow the arrows!follow the arrows!

Diagonal Rule

Now try it yourself on the blank side of the diagonal rule sheet

Doing this will be #1 on your next quiz!

Practice Using the Diagonal Rule

Work on writing the electron configurations for the 10 elements in the packet