Electron

Configuration

IB Chemistry Power Points

Topic 2

Atomic Structure

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Going beyond 2,8,8,2

Electron configuration in atoms can be described by terms called quantum numbers – no two electrons can have the same quantum number!

1st Term: shell (n)- main energy level

n = 1

n = 2

n = 3

lone electronof hydrogen

energy

Issue with this graphic?

2nd Term: subshell - designated by s, p, d, f - designates the sub-energy level within the shell.- refers to the shape(s) of the volume of space where electrons are be located.

1s

n = 2

n = 3

The first shell (1) has one subshell (s).

The s subshell has 1 spherical shaped orbital

orbitals are volumes of space where the probability of finding an electron is high

energy

The Electronic Configuration of Hydrogen

1s

Hydrogen has one electron located in the first shell. (Aufbau principle – electrons will occupy the lowest energy orbitals first)

The first shell has only one subshell (s). The s subshell holds a single s orbital.

1s1

shell

subshell

# of electrons present

energy

1s

Electronic configuration

Orbital Energy Level Diagram

The Electronic Configuration of Helium He: Atomic # of 2, 2 electrons in a neutral He atom

H 1s1

He 1s2

He 1s 1s

the maximum number of electrons in an orbital is TWO

if there are 2 electrons in the same orbital they must have an opposite spin.

This is called Pauli’s Exclusion Principle

energy

1s

Lithium (Li)Li: Z=3 Li has 3 electrons.

2nd shell

1s

The 2nd shell (n= 2) has 2 subshells which are s and p.

The s subshell fills first! (Aufbau Principle)

2s 2p

Li 1s22s1

2s

Li 1s

Electronic configuration

Orbital Energy Level Diagram

energy

Subshells so far - designated by s, and p - refers to the shape(s) of the volume in which the electron can be located. - also designates an energy level within the shell. - relative energy: s < p

s subshell: spherical1 orbital

p subshell: pair of lobes, 3 orbitals, each holds 2 electrons

x y z

x

y

z

Berylium (Be)Be: Z=4 Be has 4 electrons.

Be 1s22s2 2s Be 1s

Electronic configurationOrbital Energy Level Diagram

1s2nd

shell2s 2p

B 1s22s22p1

2p 2s

B 1s

Boron (B) has 5 electrons, the s subshell is full so the 5th electron occupies the first orbital in the p subshell

energy

Carbon (C)C: Z=6 C has 6 electrons.

1s2nd

shell2s 2p C 1s22s22px

1py1

2p 2s

C 1s

C 1s22s22p2

The 6th electron occupies an empty p orbital. This illustrates “Hund’s Rule” – electrons do not pair in orbitals until each orbital is occupied with a single electron.

The electron configuration is

But always written as

2p 2s

N 1s 1s22s22p3

2p 2s

O 1s 1s22s22p4

2p 2s

Ne 1s 1s22s22p6

Practice

Use the sheets provided to fill out orbital diagrams and determine the electron configuration for the following elements 

1. Fluorine 2. 56Fe3. Magnesium - 224. 131I5. Potassium – 426. 75Ge7. Zirconium – 908. 41Ca2+

Practice

Use the sheets provided to fill out orbital diagrams and determine the electron configuration for the following elements 

1. Fluorine 1s22s2p5

2. 56Fe 1s22s2p63s23p64s23d6

3. Magnesium – 22 1s22s2p63s2

4. 131I 1s22s2p63s23p63d104s24p64d105s25p5

5. Potassium – 42 1s22s2p63s23p64s1

6. 75Ge 1s22s2p63s23p64s23d104p2

7. Zirconium – 90 1s22s2p63s23p64s23d104p65s24d2

8. 41Ca2+ 1s22s2p63s23p6

Electron Configurations and the Periodic Table

So far, we have seen how the subshell model provides and explanation for the patterns in ionization energy we see in the periodic table.

You have also seen how to write electron configurations

Example CALCIUM 1s22s22p63s23p64s2

Principle energy level subshell # of e-

Calcium can also be written shorthand as:

[Ar]4s2

The organization of the Periodic table correlates directly to electron structure

Condensed electron configurations – for example the electron configuration of bromine can be written [Ar] 4s23d104p5

Read questions carefully – many IB questions require you to write the FULL electron configuration

You are responsible for configurations up to Z = 36 (Kr). The table works well for this with the exception of Cr and Cu

Chromium’s configuration is:

[Ar]4s13d5

Copper’s configuration is:

[Ar]4s13d10

These configurations are energetically more stable than the expected arrangements. KNOW THEM!

Electron configuration of ions:

The exception: TRANSITION METAL IONS

In general, electrons will be removed from orbitals (ionization) in the reverse order that the orbitals were filled. In other words, electrons vacate higher energy orbitals first.

When these ions form, electrons are removed from the valence shell s orbitals before they are removed from valence d orbitals when transition metals are ionized.

For example: Cobalt has the configuration [Ar] 4s2 3d7

The Co2+ and Co3+ ions have the following electron configurations.

Co2+: [Ar] 3d7 Co3+: [Ar] 3d6

Condensed electron configurations – for example the electron configuration of bromine can be written [Ar] 4s23d104p5

1. Si ___________________________2. S2- ___________________________3. Rb+ ___________________________4. Se ___________________________5. Ar ___________________________6. Nb ___________________________7. Zn2+ ___________________________8. Cd ___________________________9. Sb ___________________________

Review: the principles involved

Hund’s Rule: the most stable arrangement of electrons in orbitals of equal energy is where there is the maximum number of unpaired electrons all with the same spin.

Aufbau Principle: electrons will fill the lowest energy orbitals first

Pauli’s Exclusion Principle: A maximum of two electrons can occupy a single orbital. These electrons will have opposite spins.