Electron ConfigurationAtoms and how their electrons orbit inside them!

Quick Note!

An electron exists and moves in an orbital

An orbital has a certain shape and distance from the

nucleus

An orbital can only hold a maximum of 2 electrons

The more electrons an atom has, the more orbitals

an atom has to hold all the electrons

Quantum Numbers

Quantum numbers describe the behavior of an atom’s electrons

Quantum Numbers “n” represents the main energy level an

electron occupies

The bigger “n” gets, the further away from the

nucleus the electron gets

If more than 1 electron has the same value for

“n” they are in the same “shell”

“n” can only be in integer values; n≥1

The # of orbitals in a shell = n2

Angular Momentum Quantum Number l

l represents the shape (or sublevel) of the orbital

The value for l is an integer greater than or equal to

0

l = n – 1

Each number value corresponds to a shape

Value for l Orbital letter shape

0 s Sphere

1 p Dumbbell

2 d Butterfly

3 f Complex

Magnetic Quantum Number mm represents the orientation of the orbital about the

nucleus

The values for m can be -l, 0 , +l

The amount of m values correspond to the number of orientations of that shape

Value for m # orbitals of that shape Orbital letter shape

0 1 s Sphere

-1, 0, 1 3 p Dumbbell

-2, -1, 0, 1, 2 5 d Butterfly

-3, -2, -1, 0, 1, 2, 3 7 f Complex

Spin Quantum Number

Negative repulses negative, therefore, electrons

don’t like each other

Electrons want to always move in opposite

directions if they have to share an orbital

Spin quantum number can be +1/2 or -1/2

Quantum Numbers

Electron Configuration

The arrangement of electrons in an atom

Each element has a unique electron configuration

An element will have the orbitals of the elements

preceding it plus any additional orbitals to

account for it’s extra electrons

Ex:He has a level 1 s orbital,

Li has both a level 1 s orbital and a level 2 s orbital

Electron Configuration

Three RULES!

1. Aufbau principle: an electron occupies the lowest-

energy orbital available

If we have 5 electrons, how can we fit them so the lowest

energy orbitals fill first?

1s

2s2px 2py 2pz

Energ

y

Electron Configuration

Three RULES!

2. Pauli Exclusion Principle: no two electrons of one

atom can have the same set of 4 quantum numbers

If we have 4 electrons, but they only fill 2 energy levels,

how can we arrange them so they are different?

1s

2s2px 2py 2pz

Energ

y

Electron Configuration

Three RULES!

3. Hund’s Rule: orbitals of equal energy all fill with

one electron before a second electron may be added.

If we have 7 electrons, how can we fill the orbitals by

energy level?

1s

2s2px 2py 2pz

Energ

y

Electron Configuration

Hints!

Find the number of electrons

List all orbitals available to element

Arrange orbitals from lowest to highest energy

from left to right

Group like orbitals together

ex: put all p orbitals of one level closer together

Orbital Notation

Orbital notation is a visual notation using arrows to

represent electrons and lines to represent orbitals

H ___ He ___ B ___ ___ ___ ___ ___

1s 1s 1s 2s 2p

Electron-Configuration Notation

Electron-Configuration Notations uses the principle

quantum number, the orbital letter, and the number of

electrons in superscript

H = 1s1 He = 1s2 B = 1s22s22p1

Nobel Gas Notation

Nobel Gas Notation is a short cut notation

We know a Nobel gas will have all the orbitals up to that

Nobel gas entirely filled

Therefore, we can write a Nobel Gas plus any new orbitals

corresponding to the new element

Ca = 1s22s22p63s13p64s2 that is really long!

Ca is close to Ar; Ar = 1s22s22p63s13p6

Therefore: Ca = [Ar]4s2

Valence Electrons & Inner Electrons Every element has a set of valence electrons. For

the s and p block, there are 8 valence electrons

Electrons in the valence shell are typically in the highest occupied energy level For Argon (1s2 2s2 2p6 3s2 3p6) this is 3

For Berylium (1s2 2s2) this is 2

All non-valence electrons are inner-shell electrons

If we know an electron configuration of a neutral atom, we can figure out which element it is