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