1. FILLING ORDER – memorize! 1s_ 2s_ 2p_ _ _ 3s_ 3p_ _ _3d _ _ _ _ _
ORBITAL NOTATION
FILLING ORDER – memorize!
1s_ 2s_ 2p_ _ _ 3s_ 3p_ _ _3d _ _ _ _ _
N = 1
N = 2
N = 3
ORBITALS- PLACE WHERE ELECTRONS MOST LIKELY FOUND. Holds 2 electrons (pair) maximum.
SUBLEVELS- subdivision of a shell.
s: holds 2 electrons, (one orbital)-found in all shells
p: holds 6 electrons, (three orbitals)-second shell and up
d: holds 10 electrons, (five orbitals)-third shell and up

2. AUFBAU PROCESS: WHEN DIAGRAMMING AN ELECTRON CONFIGURATION, ELECTRONS ARE PLACED FROM THE INNERMOST(LOW ENERGY) TO THE OUTERMOST(HIGH ENERGY) ORBITALS IN ORDER. ONLY THE OUTERMOST ORBITAL AND SUBLEVEL MAY BE UNFILLED (EXCEPT FOR SOME TRANSITION METALS).
HUNDS RULE: WHEN FILLING A p, d, OR f SUBLEVEL YOU MUST ADD ONE ELECTRON FIRST AND THEN GO BACK AND PAIR THEM UNTIL ALL ELECTRONS ARE SHOWN.
p _ _ _
PAULI EXCLUSION PRINCIPLE: ELECTRONS IN AN ORBITAL MUST HAVE OPPOSITE SPIN NOTATION, ONE HAS AN UP ARROW , ANT THE OTHER A DOWN ARROW,

3. FIRST SHOW 2 ARROWS(ELECTRONS) IN THE FIRST SHELL
FILLING ORDER
1s_ 2s_ 2p_ _ _ 3s_ 3p_ _ _ 3d _ _ _ _ _ Na 11
2-8-1
EX) Show the electron configuration of
1s_ 2s_ 2p_ _ _ 3s_ 3p_ _ _ 3d _ _ _ _ _ 2 8 1
THE PERIODIC TABLE INDICATES ONLY ONE ELECTRON (ARROW) IN THE THIRD SHELL. THIS IS THE VALENCE, AND YOU ARE NOW DONE!
After the first shell has 2 electrons, place 8 electrons in shell n=2 as indicated on the periodic table ground state
FIRST SHOW 2 ARROWS(ELECTRONS) IN THE FIRST SHELL