Writing Electron Configurations

Three ways to do it

First, a clever look at the atom

Atom NOVA

The Way That Almost Forced Me from Chemistry

Actually, it's not so bad,

and millions find it their

favorite method.

Try it with Na, Cl and Fe. . .

Aufbau rule: electrons always occupy the lowest energy level available. Find it on this diagram.

The Periodic Table Method

From U.Cal Davis

1

2

3

4

5

6

7

s pd

f

n-1

n-2

n

The Verbal Memory Method

This takes a while, but it's a good check on the other methods

Memorize 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Exceptions

There is a “pull” toward half-filled and completely filled degenerate orbitals: lower energy state than the alternative

Example: 4s2 and 3d9 vs 4s1 and 3d10

This works with ions as well: explains Ag+

Always think: what if we took one, two or three electrons away from this atom

And, what if we add electrons to this non-metal