Chapter 5: Electrons in Atoms

Section 2:Electron Arrangement in Atoms

Apply the aufbau principle, the Pauli exclusion principle, and Hund’s Rule to generate electron configurations and spin diagrams;

Explain that there can be exceptions to the normal rules for electron configurations; and

Draw modified Bohr diagrams for atoms

Student will be able to:

Electron’s address

Energy level Sublevel Orbital Spin

Where do electrons live?

Need a system for electron addresses...

•Your address • State • Town • Street • House

Energy levels are numbered(1, 2, 3...) Each energy level adds one more

sublevel (letters) Each sublevel adds two more orbitals

Sublevels and orbitals

Energy Level

Sublevels and orbitals

1 s (one orb.)2 s (one orb.), p (three orbs.)3 s (one orb.), p (three orbs.), d (five

orbs.)4 s (one orb.), p (three orbs.), d (five

orbs.), f (seven orbs.)

Sublevels addressed by the number of their energy level and letter of sublevel◦ Example: 1s, 2s, 2p, 3s, 3p, 3d

Still two more parts to address (orbital and spin)...

Electron configuration: arrangement of electrons in an atom in its ground state

Orbital diagram: illustrates arrangement and spin of electrons

Keeping track of all the sublevels

Aufbau principle: electrons occupy orbitals of lowest energy first

Electrons (like some students) are lazy Orbitals in same sublevel are same energy

Rules for Electron Configurations

Pauli Exclusion Principle Orbital can hold maximum

of two electrons ◦ (Two per seat on the bus)

If two electrons in an orbital, must be opposite spins

Two possible spins: up and down

Rules for Electron Configurations

Hunds Rule Orbitals in same sublevel are same energy Electrons fill orbitals of same energy so

they maximize same spin Students don’t pair up in a seat until they

have to

Rules for electron configurations

One electron for every proton Periodic table arranged by atomic number Typewriter method: start at H, read left to

right, and stop at the element you’re configuring

Putting the rules to use...

Further down the table... La starts 4f sublevel

◦ Comes after 6s and before 5d◦ Lu is actually 5d1

Ac starts 5f sublevel◦ Comes after 7s and before 6d◦ Lr is actually 6d1

Try some...

There are exceptions to the normal rules for electron configurations

Based on stability Just know that they exist, not how to do

them

Just when you learn the rules...

Atom drawn with nucleus in center and one ring for each energy level

Electrons drawn as dots on the rings Example: S 1s2, one ring, 2 dots 2s2, 2p6, one ring, 8 dots 3s2, 3p4, one ring, 6 dots

Bohr Diagrams

Group electrons by sublevels Show spins Example: S 1s2

◦ one ring, 2 arrows paired 2s2, 2p6

◦ one ring, 2 arrows paired (s), 6 arrows paired (p)

3s2, 3p4

◦ One ring, two arrows paired (s) four arrows with two paired (p)

“Modified” Bohr Diagrams

16 p16n

Apply the aufbau principle, the Pauli exclusion principle, and Hund’s Rule to generate electron configurations and spin diagrams?

Explain that there can be exceptions to the normal rules for electron configurations?

Draw modified Bohr diagrams for atoms?

Can you…?

Page 135 & 136, 8-13

Homework