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• Aufbau Principle - states that electrons fill ORBITALS with the lowest possible energy to the highest energy.

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• EX: school bus

Orbital Diagrams

• Graphical representation of the electrons in an atom’s electron cloud

• One arrow represents one electron

• Shows spin and which orbital within a sublevel

• Same rules as before (Aufbau principle, d4 and d9 exceptions, two electrons in each orbital, etc. etc.)

Carbon

Group 4A

Atomic number = 6

1s2 2s2 2p2 --->

6 total electrons

Here we see for the first time

HUND’S RULE. When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible.

1s

2s

3s

3p

2p

Electron Configurations

• A list of the main energy levels, sublevels, and electrons in an atom (or ion)

• Must go in order of filling (Aufbau principle)

• 2 electrons per orbital, MAXIMUM

• Used to determine the element and valence e’

2p4

Order of filling…e’ fill the orbitals closest to the nucleus

s

s 3p 3d

s 2p

s 4p 4d 4f

s 5p 5d 5f

s 6p 6d 6f

s 7p 7d 7f

1

2

3

4

5

6

7

Orbitals and the Periodic Table

s, p, d, and f blocks http://www.ptable.com/