Orbitals are areas inside an energy level surrounding the nucleus that house electrons It indicates the likely location of the electron. They are houses of the electrons, also called as sub-levels. There are four different orbitals – s, p, d & f. You can differentiate the orbitals by their difference in their maximum number of electrons that can be placed for every orbital. For the s orbitals, you can have a maximum of 2 electrons. For the p orbitals, you can have a maximum of 6 electrons. For the d orbitals, you can have a maximum of 10 electrons. For the f orbitals, you can have a maximum of 14 electrons. There is 1 orbital for the s sub-level, 3 orbitals for the p sub-level, 5 orbitals for the d sub-level and 7 orbitals for the f sub-level.
There are three principles behind writing down electron configurations and orbital notations properly. They are the Aufbau Principle, the Pauli Exclusion Principle and Hund’s Rule. Aufbau is in german and it means ‘building up’. It means that electrons occupy orbitals in the order of increasing energy, starting with 1s2 2s2 2p6 3s2 and so on. The Pauli Exclusion Principle states that each electron has its own unique set of four quantum numbers. They may have the same principal quantum number, the same orbital angular momentum quantum number, and the same magnetic quantum number but they have different spin magnetic quantum numbers. The Hund’s Rule states that when electrons go to their orbitals, they have to take up the the empty orbitals before double occupying them.
Example: Rubidium
Electron Configuration
To fill this table, one should need: Number of orbital & Electron number
| Principle energy level | Type of sub-level | Number of orbitals per type | Number of orbitals per level | Number of electron |
| 1 | s | 1 | 1 | 2 |
| 2 | s
p |
1
3 |
4 | 8 |
| 3 | s
p d |
1
3 5 |
9 | 18 |
| 4 | s
p |
1
3 |
4 | 8 |
| 5 | s | 1 | 1 | 1 |
Fig 1
Example of how electron configuration works
How it works:
- First, you mus
t group the principle energy level to its corresponding tyoe of sublevel. (1s , 2s, 2p,5s) - After grouping the principle energy level and the type of sublevel, format it in the way shown in the figure to the right. Place all the same principle levels of energy together.
- After doing so, cross it each out with a diagonal line. (example: 1s in on diagonal while 7s,6p,5d and 4f are in the same diagonal). This should give you something like this: 1s 2s 2p 3s 3p 4s
- With the given one above, just input the amount of electrons (each orbital has at most 2 electrons). Example : 1s2 , 2s2, 2p6
Electron configuration of Rubidium:
1s2 2s2 2p6 3s2p6d10 4s2p6 5s1
Orbital Notation
Orbital notation is the drawing counterpart of the electron configuration. It helps in determining the electron pairing.
In the image, you can that 1s and 2s have 2 arrows since S corresponds to two electrons while 2p has 3 because p corresponds to 3 electrons
Sources:
http://www.uwplatt.edu/~sundin/114/image/l1423d.gif
http://environmentalchemistry.com/yogi/periodic/Rb.html
http://www.mrbigler.com/Chem1-C1/topics/quantum/Lewis-dot-diagrams_files/image003.gif
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