Chapter 13: Orbitals Chapter 13: Orbitals and Electron and Electron Configurations Configurations Atomic Orbitals and Electron Configurations (Chap 13)Atomic Orbitals and Electron Configurations (Chap 13)

Quantum Mechanics Quantum Mechanics (Heisenburg and Schrodinger)(Heisenburg and Schrodinger)

http://www.meta-synthesis.com/webbook/30_timeline/310px-Bohr-atom-PAR.svg.pnghttp://www.meta-synthesis.com/webbook/30_timeline/310px-Bohr-atom-PAR.svg.png

Better than any previous model, Better than any previous model, quantum mechanics does quantum mechanics does explain how the atom behaves. explain how the atom behaves.

Quantum mechanics treats electrons not as particles, but more as waves (like light waves) which can gain or lose energy.

But they can’t gain or lose just But they can’t gain or lose just any amount of energy. They any amount of energy. They gain or lose a “quantum” of gain or lose a “quantum” of energy. energy.

A quantum A quantum is just an amount of energy that the is just an amount of energy that the electron needs to gain (or lose) to move to the next electron needs to gain (or lose) to move to the next energy level.energy level.In this case it is losing the energy and dropping a level.

Atomic OrbitalsAtomic Orbitalshttp://milesmathis.com/bohr2.jpghttp://milesmathis.com/bohr2.jpg

Much like the Bohr model, the Much like the Bohr model, the energy levels in quantum energy levels in quantum mechanics describe locations mechanics describe locations where you are likely to find an where you are likely to find an electron.electron.

Orbitals are “geometric shapes” around the nucleus where electrons are found.

Quantum mechanics calculates Quantum mechanics calculates the probabilities where you are the probabilities where you are “likely” to find electrons.“likely” to find electrons.

Atomic OrbitalsAtomic Orbitalshttp://courses.chem.psu.edu/chem210/quantum/quantum.htmlhttp://courses.chem.psu.edu/chem210/quantum/quantum.html

Of course, you could find an electron Of course, you could find an electron anywhere if you looked hard enough.anywhere if you looked hard enough.

So scientists agreed to limit these So scientists agreed to limit these calculations to locations where there was at calculations to locations where there was at least a 90% chance of finding an electron.least a 90% chance of finding an electron.

Think of orbitals  as sort of a "border” for spaces around the nucleus inside which electrons are allowed.

No more than 2 electrons can ever be in 1 orbital. The orbital just defines an “area” where you can find an electron.

Sub-levels = Specific Sub-levels = Specific Atomic OrbitalsAtomic Orbitals

There are 4 types of atomic orbitals:s, p, d and fEach of these sub-

levels represent the blocks on the periodic table.

Energy LevelsEnergy Levelshttp://www.chem4kids.com/files/art/elem_pertable2.gifhttp://www.chem4kids.com/files/art/elem_pertable2.gif

Quantum mechanics has a principal quantum Quantum mechanics has a principal quantum number. It is represented by a little n. It number. It is represented by a little n. It represents the “energy level” similar to represents the “energy level” similar to Bohr’s model.Bohr’s model.n=1 describes the first energy leveln=1 describes the first energy leveln=2 describes the second energy leveln=2 describes the second energy levelEtc.Etc.

Each energy level represents a period or row on the periodic table. s sublevel begins at energy level 1p sublevel begins at energy level 2d sublevel begins at energy level 3f sublevel begins at energy level 4

OrbitalsOrbitalshttp://media-2.web.britannica.com/eb-media/54/3254-004-AEC1FB42.gifhttp://media-2.web.britannica.com/eb-media/54/3254-004-AEC1FB42.gif

http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/D_orbitals.svg/744px-http://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/D_orbitals.svg/744px-D_orbitals.svg.pngD_orbitals.svg.png

In the s block, electrons are going into s orbitals.In the s block, electrons are going into s orbitals.

In the p block, the s orbitals are full. New electrons are going into the p orbitals.In the p block, the s orbitals are full. New electrons are going into the p orbitals.

In the d block, the s and p orbitals are full. New electrons are going into the d In the d block, the s and p orbitals are full. New electrons are going into the d orbitals.orbitals.

What about the f block?What about the f block?

s p d

f-orbital = rosette f-orbital = rosette VERY COMPLICATED VERY COMPLICATED

SHAPESHAPE

Electron ConfigurationsElectron Configurations

What do I mean by “electron What do I mean by “electron configuration?”configuration?”

The electron configuration is the specific way in which the atomic orbitals are filled.

Think of it as being similar to your Think of it as being similar to your address. The electron configuration address. The electron configuration tells me where all the electrons tells me where all the electrons “live.”“live.”

No more than 2 No more than 2 Electrons in Any Electrons in Any Orbital…ever.Orbital…ever.

http://www.fnal.gov/pub/inquiring/timeline/images/pauli.jpghttp://www.fnal.gov/pub/inquiring/timeline/images/pauli.jpgThe Pauli Exclusion Principle states that an atomic orbital may have up to 2 electrons and then it is full.

The spins have to be opposite.

We usually represent We usually represent this with an up arrow this with an up arrow and a down arrow.and a down arrow.

Wolfgang Pauli, yet another German Nobel Prize winner

Hund’s RuleHund’s Rulehttp://intro.chem.okstate.edu/AP/2004Norman/Chapter7/Lec111000.htmlhttp://intro.chem.okstate.edu/AP/2004Norman/Chapter7/Lec111000.html

Hund’s Rule states that Hund’s Rule states that when you get to degenerate when you get to degenerate orbitals, you fill them all half orbitals, you fill them all half way first, and then you start way first, and then you start pairing up the electrons.pairing up the electrons.

Each orbital will get one electron before any gets two. Think of this rule as…..

“SHARE BEFORE YOU PAIR”

Don’t pair up the 2p electrons until all 3 orbitals are half full.

PRACTICE!PRACTICE!

NOW that we know the rules, we can try to NOW that we know the rules, we can try to write some electron configurations.write some electron configurations.

Remember to use your orbital filling guide to Remember to use your orbital filling guide to determine WHICH orbital comes next.determine WHICH orbital comes next.

Lets write some electron configurations for Lets write some electron configurations for the first few elements. Let’s start with the first few elements. Let’s start with hydrogen.hydrogen.

One last thing. Look at the previous slide and One last thing. Look at the previous slide and look at just hydrogen, lithium, sodium and look at just hydrogen, lithium, sodium and potassium. potassium.

Notice their electron configurations. Do you Notice their electron configurations. Do you see any similarities?see any similarities?

Since H and Li and Na and K are all in Group Since H and Li and Na and K are all in Group 1A, they all have a similar ending. (s1A, they all have a similar ending. (s11))

Electron ConfigurationsElectron Configurations

Element Configuration

H Z=1 1s1

Li Z=3 1s22s1

Na Z=11 1s22s22p63s1

K Z=19 1s22s22p63s23p64s1

This similar configuration causes them to behave the same chemically.It’s for that reason they are in the same family or group on the periodic table.Each group will have the same ending configuration, in this case something that ends in s1.

The EndThe End