Electron Configurations

BOHR’S MODEL-ELECTRON CLOUD Energy level of an

electron• analogous to the

rungs of a ladder The electron

cannot exist between energy levels, just like you can’t stand between rungs on a ladder

A QUANTUM of energy is the amount of energy

required to move an electron from one energy level to another

IN 1926, ERWIN SCHRODINGER derived an

equation that described the energy and position of the electrons in an atom

THE QUANTUM MECHANICAL MODEL

Has energy levels for electrons.

Orbits are not circular. It can only tell us the

probability of finding an electron a certain distance from the nucleus.

THE QUANTUM MECHANICAL MODEL

The atom is found inside a blurry “electron cloud”

An area where there is a chance of finding an electron.

Think of fan blades

ATOMIC ORBITALS• atomic orbitals (coined by scientists in

1932) - regions where there is a high probability of finding an electron.

Sublevels- letters s, p, d, and f

PRINCIPAL QUANTUM NUMBERGenerally symbolized by “n”, it denotes the shell (energy level/period) in which the electron is located.

Maximum number of electrons that can fit in an energy level is: 2n2

SUMMARY

s

p

d

f

# of shapes (orbitals)

Maximum electrons

Starts at energy level

1 2 1

3 6 2

5 10 3

7 14 4

ELECTRON CONFIGURATIONS… …are the way electrons are

arranged in various orbitals around the nuclei of atoms.

THREE RULES TELL US HOW:

1)Aufbau principle - electrons enter the lowest energy first.

2) Pauli Exclusion Principle - at most 2 electrons per orbital - different spins

PAULI EXCLUSION PRINCIPLE

No two electrons in an atom can have the same four quantum numbers.

Wolfgang Pauli

To show the different direction of spin, a pair in the same orbital is written as:

ELECTRON CONFIGURATIONS3) Hund’s Rule- When electrons

occupy orbitals of equal energy, they don’t pair up until they have to.

Let’s write the electron configuration for Phosphorus

The first two electrons go into the 1s orbital

Notice the opposite direction of the spins

only 13 more to go...

Incr

easi

ng e

nerg

y

1s

2s

3s

4s5s6s7s

2p

3p

4p5p6p

3d

4d5d

7p 6d

4f5f

The next electrons go into the 2s orbital

only 11 more...Incr

easi

ng e

nerg

y

1s

2s

3s

4s5s6s7s

2p

3p

4p5p6p

3d

4d5d

7p 6d

4f5f

• The next electrons go into the 2p orbital

• only 5 more...Incr

easi

ng e

nerg

y

1s

2s

3s

4s5s6s7s

2p

3p

4p5p6p

3d

4d5d

7p 6d

4f5f

• The next electrons go into the 3s orbital

• only 3 more...Incr

easi

ng e

nerg

y

1s

2s

3s

4s5s6s7s

2p

3p

4p5p6p

3d

4d5d

7p 6d

4f5f

Incr

easi

ng e

nerg

y

1s

2s

3s

4s5s6s7s

2p

3p

4p5p6p

3d

4d5d

7p 6d

4f5f

• The last three electrons go into the 3p orbitals.

They each go into separate shapes (Hund’s)

• 3 unpaired electrons Orbital

notation

HOWEVER, THERE IS AN EASIER WAY TO DO ELECTRON CONFIGURATIONS Let’s stick with P

= 1s22s22p63s23p3 Confused? Don’t be…there is an easy

way to write these things based on the positions of elements on the chart

First, grab your chart

Look at the Labels

group 1: s1 Group 2: s2 Group 3: p1 Group 4: p2 Group 5: p3 Group 6: p4 Group 7: p5 Group 8: p6 Transition

Metals: d 1-10 Lanthanide

series f: 1-14

Now, go back to P What period is P?

3 What group is P?

5 So, now we build

up: 1s1 (H), 1s2

(He), 2s1 (Li), 2s2 (Be), 2p1 (B), 2p2 (C), 2p3, (N), 2p4 (O), 2p5 (F), 2p6 (Ne), 3s1 (Na), 3s2 (Mg), 3p1 (Al), 3p2 (Si), 3p3 (P)

1s22s22p63s23p3

LET’S TRY THESE TOGETHER H

He

Li

Be

B

C

N

O

F

Ne