Electron Configuration

More complex than simple concentric circles.

Orbit vs. orbital??

-orbitthe path an electron takes (Bohr)

-orbitala region around the nucleus where an electron with a given energy is likely to be found

Orbitals and energy

-each principle energy level is divided into one or more sublevels

n=1 has one sublevel

n=2 has two sublevels

n=3 has three sublevels

Orbital Representations

Four basic orbital shapesThe s orbitals are spherical:

1s 2s 3s

p Orbitals: “peanut”

Have two lobes lying along the x, y, or z axis.

Different orientations labelled px, py, and pz.

Sodium Diagram

d Orbitals: “double p”

Have complicated shapes, but the electron density at the nucleus is always zero.

f Orbitals

orbital shape highly varied high energy electrons

How do energy levels, sublevels, and orbitals fit

together?

Orbitals and energy

-principle energy levels proposed by Bohr (n)

n=1n=2

n=3

Orbitals and energy (cont’d)

- there may be only one of each type of sublevel at each energy level

- each sublevel consists of one or more orbitals

s

p

d

f

Increasing energy

1

3

5

7

Orbitals and energy (cont’d)

-sublevels are written with the quantum number and the type of orbitals

1s 2p

energy level type of orbital

1st principle energy level (n=1)

-since n=1, there is only one sublevel

1s

-the s sublevel only consists of one orbital

-there is only 1 orbital in this energy level

2nd principle energy level (n=2)

-since n=2, there are two sublevels

2s 2p

-there is one s orbital in the 2s sublevel and three p orbitals in the 2p sublevel

-4 total orbitals in this energy level

3rd principle energy level (n=3)

-since n=3, there are three sublevels

3s 3p 3d

-there is 1 s orbital, 3 p orbitals, and 5 d orbitals

-9 total orbitals in this energy level

4th principle energy level (n=4)

How many sublevels? 4

Name the sublevels. 4s 4p 4d 4f

How many total orbitals? 16

Orbitals and energy (cont’d)

How does a 1s orbital differ from a 2s orbital?

How does a 2p orbital differ from a 3p orbital?

SIZE & ENERGY

Electron spin

-electrons behave as though they were spinning on their own axis, creating a magnetic field

-2 “types” of spin

clockwise counterclockwise

Electron spin (cont’d)

-if 2 electrons have opposite spins, they cancel each other out

-if 2 electrons have parallel spins, there is a net effect on the magnetic field

-each orbital can hold a maximum of 2 electrons

Electron spin (cont’d)

sublevel # of orbitals max. # e-

s 1 2

p 3 6

d 5 10

f 7 14

Remember Bohr’s atom (2n2)?

n=1n=2

n=3

Level (n) sublevels orbitals max. # e-

1 1 (s) 1 2

2 2 (s, p) 4 8

3 3 (s, p, d) 9 18

4 4 (s, p, d, f) 16 32

Writing electron configurations

An electron configuration shows the distribution of electrons among orbitals in an atom (location, energy).

Why is it important?

-the behavior of atoms is determined by the outer electrons (bonding)

Electron configuration (cont’d)

When writing electron configurations, you must obey three rules:

1. The Aufbau Principle

2. The Pauli Exclusion Principle

3. Hund’s Rule

The Aufbau Principle

-electrons are added one at a time to the lowest energy levels until all electrons of the atom have been accounted for

Aufbau Principle (cont’d)

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

The Pauli Exclusion Principle

-an orbital can hold a maximum of 2 electrons

-the e- must have opposite spins

-termed “paired” and “unpaired”

Hund’s Rule

-electrons occupy equal energy orbitals so that a maximum number of unpaired electrons results

-in a sublevel, you place one e- in each orbital first, the go back and pair them up

Example

lithium

3e-

1s

2e- 1e-

2sorbital diagram

e- configuration1s22s1

Example

oxygen8e- 7e- 6e- 5e- 4e- 3e- 2e- 1e-

1s 2s 2p

1s22s22p4

Practice Problem

Write the orbital diagram and electron configuration for sodium.

1s 2s 2p 3s

1s22s22p63s1

Practice Problem

Write the orbital diagram and electron configuration for nickel.

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

1s22s22p63s23p64s23d8

H 1s1

He 1s2 full Noble gasLi 1s2,2s1

Be 1s2,2s2

B 1s2,2s2p1

C 1s2,2s2p2

N 1s2,2s2p3

O 1s2,2s2p4

F 1s2,2s2p5

Ne 1s2,2s2p6 full Noble gas

Valence Electrons in YellowYellow

Electron Configurations and the Periodic Table

Write electron configurations for:

13Al:

[Ne] 3s2 3p1

1s2 2s2 2p6 3s2 3p1

50Sn: [Kr] 5s2 4d10 5p2

82Pb+2: [Xe] 6s2 4f14 5d10

92U: [Rn] 7s2 6d1 5f3

26Fe: [Ar] 4s2 3d6 [Ar]4s 3d