Electron ConfigurationA method we use to keep track of how electrons are arranged in an atom.

It helps us to explain why atoms react the way they do.

H 1s1

Energy LevelSub-level

# of electrons in sub-level

The arrangement of the electrons may be represented in one of three ways.

This is how hydrogen would be shown using spectroscopic notationElectron configuration may also be shown with box diagrams.

Electron Configuration

A box is used to represent each orbital.

An arrow is used to represent each electron.

H 1s1 These may also be called orbital box diagrams or orbital filling diagrams.

Circles may also be used instead of boxes.Helium has 2 electrons:

He 1s2

Electron Configuration

Here are some more:

Li 1s2 2s1

Be 1s2 2s2

B 1s2 2s2 2p1

C 1s2 2s2 2p2

N 1s2 2s2 2p3

O 1s2 2s2 2p4

F 1s2 2s2 2p5

Ne 1s2 2s2 2p6

This arrangement (filled s & p in the outer energy level) is called a stable octet.

SpectroscopySpectroscopyHow do we know that there are e- subshells in an atom?

Actually, the same way we first found out about energy levels - Spectroscopy

Many different forms of spectroscopy are used to determine charateristics and structural features for atoms and molecules

• UV/Vis Emission Spectroscopy• Mass Spectroscopy• Nuclear Magnetic Resonance Spectroscopy• AA spectroscopy (UV)• IR Spectroscopy (Bond types/functional groups)• XPS – X-ray Photoelectron Spectroscopy (PES)

XPS uses X-rays generated from Al or Mg atoms that are focused by a small quartz crystal onto a sample of an element or compound.The energy is absorbed by electrons in different shells (or subshells) and they jump out of the atom.

The KE of an electron is measured by a detector and is subtracted from the energy of the X-ray photon.

This value represents the amount of energy that was necessary to remove that particular electron.

Energy values and peak heights are plotted (Relative # of e- vs. Energy) For reasons I have yet to figure out, energy values are plotted backward (highest energy on the left, lowest on the right).These values can be compared to determine # of electrons in a shell, or compared with known spectra to determine the identity of an element.