Electron
Configurations!
 e-
are arranged in up to 7
energy levels
 Lower E levels fill up first
(Aufbrau principle)
 E levels have 4 orbitals: s,p,d,f
 2 electrons per orbital (Pauli)
Electron configurations
describe where the electrons
are in a given atom.
Hydrogen, for example, has
one electron in a spherical s
orbital.
 There is a high probability
that the electron is
somewhere in this “cloud”, a
certain radius from the
nucleus.
The S denotes the electron is in the S
orbital.
 1 denotes the electron is in period 1.
 Superscript 1 denotes there is 1
electron in the 1S orbital.
Therefore, the electron
configuration for hydrogen is:
1S1
The electron configuration
for helium is 1S2

Meaning, there are 2 electrons in the 1S
enegy level of helium!
Lithium has 3 electrons
 However an S orbital can only hold a
maximum of 2 electrons
 Therefore Li has 2 1S electrons and 1 2S
electron 1S22S1

Beryllium is 1S22S2

Since S orbitals can only hold 2
electrons, the 5th electron, found in
boron creates a new orbital, called a
“p”.
Our next element boron, B has
one more electron than Be.

Since S orbitals can hold a maximum of 2,
the new electron creates a new “p”
orbital. This is balloon shaped and the
orbitals exist in pairs along 3 axes, x, y
and z in the second shell.

Boron is 1S22S22p1
 As each atom adds another electron, into
the p orbital, the electron # goes to 2, 3. 4.
5. and 6 with Ne. Therefore C is

1S22S22p2
Ne is 1S22S22p6
 Notice the first number is the shell
 the letter is the orbital shape
 the superscript is the number of e
Notice how different this looks compared
to prior models:
D orbitals are different than s or p:
When we get to the d
suborbital,
d electrons have lower energy
than s or p electrons
Therefore Sc has a 3d electron.
The d electron is in the third
energy level:
1S22S22p63s23p64S23d1
The Periodic Table has s, p, d, f
blocks:…
Notice the s, p, d, f electron
configs for valence e-
Shortcuts: You can write a shortcut to
the electron configuration by going
back to the last noble gas, putting it
in brackets, and then adding the
outer shell.
 Example: Mg, 1S22S22p63s2 becomes
[Ne]3s2

Question:

Knowing electron configurations:
Hot or Not?
Definitely HOT!
The End