Electron+Address

Quantization and Electron Arrangement
The modern atomic model contains four major pieces of information about an element's electrons and their arrangements within its atoms.


 * __energy level__:** this is also called the //principal quantum number// (n), and it ranges from 1 to 7. These are the horizontal rows on the periodic table, from top to bottom. For example, calcium is in the fourth energy level (it has n = 4).

Two areas of the table are actually offset: first, the transition metals, starting at Sc, begin at energy level 3; second, the rare earth metals, starting at Ce, begin at energy level 4. This has to do with the energy associated with order of filling, which you can see below.




 * __sublevel__:** this is also known as the //angular momentum quantum number//, or //secondary quantum number// (symbol l, lower-case letter 'ell'). The ranges for l are from 0 to n - 1.

For example:

The fourth energy level has a principle quantum number n = 4.

Therefore, the secondary quantum number, l, can be l = 0 to n =1, or 0 to 3:

l = 0, which corresponds to the assigned letter "s";

l = 1, which corresponds to the assigned letter "p";

l = 2, which corresponds to the assigned letter "d";

l = 3, which corresponds to the assigned letter "f".

So the fourth energy level has four major categories, called //sublevels//, labeled s, p, d, and f. See the diagram below, which shows how the four sublevels are arranged on the periodic table.


 * __orbital__:** this is also known as the //magnetic quantum number//, (ml, called "m sub ell"), and it refers to the probability density plots about the nucleus that the electron(s) may travel in. Each sublevel has a series of orbitals, as shown below. Each orbital may hold at most two electrons.

The number of orbitals is determined by the formula:

m l = +l to -l (positive 'ell' to negative 'ell')

For example, look at the third energy level, which has n = 3, and l = 0, 1, 2 (or s, p, and d):

What this means is that for each l:

if l = 0, m l = 0 (one "s" orbital); if l = 1, m l = -1, 0, +1 (three "p" orbitals); and if l = 2, m l = -2, -1, 0, +1, +2 (five "d" orbitals).




 * __spin__:** also known as the spin quantum number (m s, called "m sub ess") which refers to an electron's spin state, which is either 'spin up' or 'spin down:

m s = +1/2 or -1/2



When electrons pair up in an orbital, they must have opposite spins, analogous to pairing up a couple of bar magnets - which would need opposite poles to stick together.

Electron spin is in fact what gives magnets their properties. Metals such as iron have many electrons with the same spin direction occupying some orbitals individually. The effect of having trillions upon trillions of iron atoms' unpaired electrons spinning in the same direction generates a magnetic field.