Energy Levels:
Electrons do not orbit the nucleus randomly; they occupy certain fixed energy levels. Each atom has its own unique set of energy levels, which are difficult to calculate but which depend on the number of protons and electrons in the atom.
Energy levels in an atom can be numbered 1, 2, 3,... to infinity. 1 is the lowest energy level (closest to the nucleus) and energy level infinity corresponds to the energy of an electron with is not attracted to the nucleus at all. The energy levels thus converge as they approach infinity
Energy levels in an atom can be numbered 1, 2, 3,... to infinity. 1 is the lowest energy level (closest to the nucleus) and energy level infinity corresponds to the energy of an electron with is not attracted to the nucleus at all. The energy levels thus converge as they approach infinity
Orbitals and Sub-Levels:
Electrons do not in fact orbit the nucleus in an orderly way. In fact they occupy areas of space known as orbitals. The exact position of an electron within an orbital is impossible to imagine; an orbital is simply an area of space in which there is a high possibility of finding an electron.
Common Orbital Shapes:
S-Orbitals:
In addition, the third and subsequent energy levels each contain five D-Orbitals, the fourth and subsequent energy levels contain seven F-Orbitals and so on.
Each type of orbital has its own characteristic shape.
S, P and D Orbitals do not all have the same energy. In any given energy level, S-Orbitals have the lowest energy and the energy of the other orbitals increases in the order p < d < f etc. Thus, each energy level must be divided into a number of different sub-levels, each of which has a slightly different energy.
The number and type of orbitals in each energy level can thus be summarised as follows:
S-Orbitals:
- These are spherical
- Every energy level contains one S-Orbital
- An S-Orbital in the first energy level is a 1s orbital
- An S-Orbital in the second energy level is a 2s orbital etc.
- There are shaped like a 3D figure of eight
- They exist in groups of three.
- Every energy level except the first level contains three P-Orbitals.
- Each P-Orbital in the same energy level has the same energy but different orientations: x, y and z
- A P-Orbital in the second energy level is a 2p orbital ( 2p(x), 2p(y), 2p(z) )
- A P-Orbital in the third energy level is a 3p orbital ( 3p(x), 3p(y), 3p(z) ) etc.
In addition, the third and subsequent energy levels each contain five D-Orbitals, the fourth and subsequent energy levels contain seven F-Orbitals and so on.
Each type of orbital has its own characteristic shape.
S, P and D Orbitals do not all have the same energy. In any given energy level, S-Orbitals have the lowest energy and the energy of the other orbitals increases in the order p < d < f etc. Thus, each energy level must be divided into a number of different sub-levels, each of which has a slightly different energy.
The number and type of orbitals in each energy level can thus be summarised as follows:
Energy Level |
1st Sub-Level |
2nd Sub-Level |
3rd Sub-Level |
4th Sub-Level |
5th Sub-Level |
1 |
1 x 1s |
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2 |
1 x 2s |
3 x 2p |
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3 |
1 x 3s |
3 x 3p |
5 x 3d |
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4 |
1 x 4s |
3 x 4p |
5 x 4d |
7 x 4f |
|
5 |
1 x 5s |
3 x 5p |
5 x 5d |
7 x 5f |
9 x 5g |
Shells:
- Different sub-levels have different energies, and the energies of the different levels get closer and closer together with increasing energy level number.
- The higher energy sub-levels of some energy levels soon end up overlapping with the low energy sub-levels of higher energy levels, resulting in a more complex energy level diagram.
- Starting with the lowest energy, the orbitals can thus be arranged as follows:
- Many of these sub-levels have similar energy, and can be grouped together.
- A collection of sub-levels of similar energy is called a shell.