Electron Configuration

Orbital shapes are defined as the surface that contains 90% of the total electron probability.

An orbital is a region within an atom where thereis a probability of finding an electron. This is a probability

diagram for the s orbital in the first energy level…

Orbitals of the same shape (s, for instance) grow larger as n increases…

Nodes are regions of low probability within an orbital.

Sizes of s orbitals

Electron Probability and Shape of Orbitals: s orbitals

Electron Probability and Shape of Orbitals: p orbitals

Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells”

…and a “dumbell with a donut”!

d orbital shapes

Shape of the f orbital

Orbital Diagrams

• diagram used to show how the electrons are distributed among the orbitals of a subshell– orbital is represented by a circle or square– electrons represented by an arrow

• Example: Hydrogen

Pauli Exclusion PrincipleNo two electrons in an atom can have the same four quantum numbers.

Wolfgang Pauli

And, no two fans in the Superdome should have the same 4 seat numbers!

Pauli Exclusion Principle

• An orbital can hold at most two electrons, and then only if the electrons have opposite spin– each electron is an atom has a unique set of

quantum numbers

• Example: Helium

Sample Problem

• Based on the Pauli exclusion principle, which of the following orbital diagrams are possible?

2s1s

1s 2s 2p

1s 2s 2p

1s 2s 2p 3s 3p

Hund’s RuleThe most stable arrangement

of electrons is that with the most unpaired electrons all

with the same spin

Hund’s Rule• the lowest energy arrangement is obtained by

putting e- in separate orbital of a subshell with parallel spin before pairing e-

• Example: Carbon– Z = 6: 1s2 2s2 2p2

• You try Oxygen– Z = 8

1s 2s 2p

1s 2s 2p

A. General Rules

Pauli Exclusion PrincipleEach orbital can hold TWO electrons with

opposite spins.

RIGHTWRONG

A. General Rules

Hund’s RuleWithin a sublevel, place one e- per orbital before

pairing them.“Empty Bus Seat Rule”

Electrons in an atom will occupy the lowest-energy

orbitals available

(aufbau = “building up”)

Energy Level Sublevel Orbitals # of

Electrons

1 s 1 2

2 sp

13

26

3spd

135

26

10

4

spdf

1357

26

1014

Sometimes the arrows are hard to follow. Here is a list of the sublevels in order. All you need to do is count up the number of electrons in order until you get to the number that matches or is slightly above the number you are looking for.

1s2 - 2s2 - 2p6 - 3s2 -

3p6 - 4s2 - 3d10 - 4p6 -

5s2 - 4d10 - 5p6 - 6s2 -

4f14 - 5d10 - 6p6 - 7s2 -

5f14 - 6d10 - 7p6

Diagonal Rule (Aufbau Principle)

Orbital filling table

Orbital Filling Order

A. General Rules

Aufbau PrincipleElectrons fill the

lowest energy orbitals first.

“Lazy Tenant Rule”

Orbital DiagramsOrbital Diagrams are models of electron arrangements showing configuration, subshell, aufbau,

hunds, and pauli

H: [ ]1S

O 8e-

• Orbital Diagram

• Electron Configuration

1s2 2s2 2p4

B. Notation

1s 2s 2p

s-block1st Period

1s11st column of s-block

1 2 3 4 5 6 7

C. Periodic Patterns

Example - Hydrogen

• Shorthand Configuration

S 16e-

Valence ElectronsCore Electrons

S 16e- [Ne] 3s2 3p4

1s2 2s2 2p6 3s2 3p4

B. Notation• Longhand Configuration

[Ar]

1 2 3 4 5 6 7

4s2 3d10 4p2

C. Periodic Patterns

Example - Germanium

Orbital occupancy for the first 10 elements, H through Ne

He and Ne have filled outer shells: confers chemical inertness

Sample Problem• Electron Configuration of Vanadium

• Quantum Numbersn =l = ml =ms =

1s 2s 2p 3s 3p 4s 3d

Exceptions• Some transition metals do not follow the

diagonal rule!

• Example: chromium– Z = 24– diagonal rule

• 1s2 2s2 2p6 3s2 3p6 4s2 3d4

-filled and half-filled orbitals are more stable than unevenly filled orbitals.

– true electron configuration• 1s2 2s2 2p6 3s2 3p6 4s1 3d5

CopperEXPECT: [Ar] 4s2 3d9

ACTUALLY: [Ar] 4s1 3d10

Copper gains stability with a full d-sublevel.

D. Stability - Exceptions

ChromiumEXPECT: [Ar] 4s2 3d4

ACTUALLY: [Ar] 4s1 3d5

Chromium gains stability with a half-full d-sublevel.

Electronic Structure of Atoms

•Shells of an atom contain a number of stacked orbitals

Shells and Orbitals

Electronic Structure of Atoms

• Some orbital subshells overlap others in different energy levels.

1

2

3

4

5678

s p d f

Relative Energies of the orbitals

Relative Energies for Shells and Orbitals

IONS

Fe: [Ar] 4s2 3d6 Fe2+: [Ar] 3d6

• Notice for iron the 4s electrons are lost - typical

for the transition metals; the 4s (or 5s) electrons

are lost first

Na Na+ + e-

1s2 2s2 2p6 3s1 1s2 2s2 2p6

F + e- F-

1s2 2s2 2p5 1s2 2s2 2p6

electron configurationof neon