IONISATION ENERGY

Now, everyone this is where I get really EXCITED - you'll see the connection later - as this is my favourite part.

Plasma is a super heated gas that has become ionised. This means that the electrons have enough energy to break from their shell and move around (though they don't fly off into distance). 

Though now we're getting into the physics field so I have to be careful as some chemists simply dislike physics (God knows why - Physics person myself).

You may be asking what has all of this got to do with ionisation energy? Good question, not much, well maybe a little. 

Ionisation energy is the energy required to remove 1 mole of electrons from 1 mole of atoms in a gaseous state.

In a plasma, electrons get freed but they need some energy to get excited (there now - get it) and leave their shell. This is the ionisation energy though in this case the electrons get removed from the compound completely to form an ion. So unlike in a plasma where the electrons swim in a "sea" surrounding the positive ions (like in a metal) during ionisation the electron is removed to produce an ion.

The ionisation is influenced by three main factors:

• Nuclear charge: As it increases the attraction on the outer electron increases so ionisation energy increases.
• Electron shielding: As the number of shells increases the ionisation energy decreases as there is a weaker attraction on the outer electron.
• Atomic radii: The further away an electron is from the nucleus (so the greater the radius) the easier it is to remove it as the attraction of the nucleus on it is much weaker, so ionisation energy decreases.

Electrons exist in shells AKA quantum levels. Each shell is made from different sub shells. Each sub shell contains only the same type of orbitals and each orbital can only hold 2 electrons of opposite spin.

ORBITAL: A region that can only hold 2 electrons of opposite spin.

SUB SHELL: A group of the same type of atomic orbitals within a shell.

SHELL: A group of orbitals with the same quantum number.

If we now image one electron as a cloud, as it very difficult to know the exact position of an electron we will just assume that the electron can be anywhere within that cloud. This an atomic orbital. If we have two electrons, we don't have two clouds (or regions where the electron can be) - it's one orbital but twice as dense.

Those clouds - orbitals - can take various shapes, when they overlap even stranger things happen. Remember the orbitals are 3D and you do not need to know all the orbital shapes only these:

• S - Orbital: Spherical in shape. Each shell contains only one s-orbital therefore in one shell this gives a total of 2 electrons.
• P - Orbital: Dumb bell shape. There can be up to 3 p orbitals in each shells so a total of 6 electrons.
• D - orbital: Up to 5 orbitals in each shell. Total of 10 electrons in a shell.
• F - Orbital: Up to 7 orbitals in each shell. Total of 14 electrons in a shell.

This is a scary overview of how all the combinations of orbitals look. Below are the shapes you actually do need to know.

Lastly you may need to give an electron configuration so use your periodic table to correctly identify the orbitals and the number of electrons in a shell. Also remember that the 4s orbital is filled in first before the 3d orbital. The 4s orbital is also emptied before the 3d orbital. This is because the 4s orbital has a lowe energy level thatn 3d.

Let me give you a couple of examples:

O: 1s2 2s2 2p4

CA: 1s2 2s2 2p6 3s2 3p6 4s2

Fe: 1s2 2s2 2p6 3s2 3p6 4s2 3d6

Here are some rules to help you get your head round it all (it is a very confusing chapter but you'll be all right. 

• Electron fill in the lowest energy level first.
• Each orbital is filled with a single electron first before pairing starts.
• When two electron enter the same orbital they must have opposite spins.

Its like old ladies on a bus, they will fill in from the front first and sit on separate seats and when all have been filled singly then they sit next to someone else.