Understanding Electron Configurations and Orbital Diagrams in Atomic Structure, Study notes of Chemistry

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ELECTRON

CONFIGURATIONS

ELECTRON CONFIGURATIONS,

ORBITAL DIAGRAMS, AUFBAU

PRINCIPLE, HUND’S RULE

REPRESENTING ELECTRONS ...

Now that you know what an orbital is, you need to be able to use that to describe the electronic nature of an element

Two ways:

Electron configuration is a concise way to describe where the electrons are with respect to energy level and sublevel

Orbital diagrams are a visual way to describe where the electrons are with respect to energy level and sublevel

AUFBAU PRINCIPLE

Aufbau described the filling order of the orbitals (ie what order do the electrons go in)

He said they must be filled from lowest energy to highest energy

Like in BR diagrams, you filled the first shell before you moved on to the second shell...but it gets more complicated!

Sadly, they don’t go numerically: 4S is lower in energy than 3D!

LINK TO QUANTUM

How do we know how many sublevels there are in a shell? For example, what sublevels exist for first shell (n=1)? when n=1, l=0 ONLY so 1s is the only sublevel

What about when n=2?

l=0 or 1 2s and 2p exist What about when n=3? l=0 or 1 or 2 3s and 3p and 3d exist

s

s 3p 3d

s 2p

s 4p 4d 4f

s 5p 5d 5f 5g?

s 6p 6d 6f 6g? 6h?

s 7p 7d 7f 7g? 7h? 7i?

1 2 3 4 5 6 Steps:

1. Write the energy levels top to bottom.
2. Write the orbitals in s, p, d, f order. Write the same number of orbitals as the energy level
3. Draw diagonal lines from the top right to the bottom left.
4. To get the correct order, follow the arrows! By this point, we are past the current periodic table so we can stop.

8

ORBITALS & THE PERIODIC TABLE

• Orbitals grouped in s, p, d, and f orbitals
• Knowing the blocks is up to you!

s orbitals p orbitals

d orbitals

f orbitals

How many electrons

can be in a sublevel? Remember: A maximum of two electrons can be placed in an orbital. s orbitals d orbitals Number of orbitals

Number of electrons

p orbitals f orbitals

1 3 5 7

ELECTRON CONFIGURATIONS

2p

Energy Level

Sublevel

Number of electrons in the sublevel

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6

6s^2 4f^14 … etc.

SHORTHAND NOTATION

A way of abbreviating long electron configurations

Since we are only concerned about the outermost electrons, we can skip to places we know are completely full, i.e. the noble gases , and then finish the configuration

SHORTHAND NOTATION

Chlorine

Longhand is 1s^2 2s^2 2p^6 3s^2 3p^5 You can abbreviate the first 10 electrons with a noble gas, Neon. [Ne] replaces 1s^2 2s^2 2p^6 The next energy level after Neon is 3 So you start at level 3 on the diagonal rule (all levels start with s) and finish the configuration by adding 7 more electrons to bring the total to 17 [Ne] 3s^2 3p^5

F BLOCK

Any element past #57 will have f block electrons

Let’s try Hg (#80)

[Xe] 6s^2 4f^14 5d^10

Electrons are divided between core & valence electrons

Core = [Ar] 3d^10 , valence = 4s^2 4p^5

B 1s^2 2s^2 2p^1

Write the electron configuration of Boron and determine how many valence electrons Boron has Core = [He] Valence = 2s^2 2p^1 Write the electron configuration of Bromine and determine how many valence electrons Br has

Br [Ar] 4s^2 3d^10 4p^5

VALENCE ELECTRONS

VALENCE ELECTRONS

• Valence electrons are always found in the OUTERMOST

shell.

• It doesn’t matter in the order they are written in!
• Always the shell with the highest principal number

How many valence electrons?

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 8 ve