Electron Configuration


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Electronic Structure
Electrons do not orbit the nucleus randomly, they occupy fixed energy levels , each atom has a
unique set of these, which makes them difficult to identify, they depend on the number of protons
and electrons in the atom.
Principal energy levels are numbered consecutively: 1,2,3 etc. 1 is the smallest and is closest to the
nucleus, whereas infinity would be not attracted to the nucleus as all, so would be far away, thus,
the levels converge as they approach infinity.
Subsidiary levels exist in each atom (sub-levels) these are given the letters S, P, D and F. These
correspond to an increase in energy. Each additional electron goes into the sub-level with the lowest
S: 2 P: 6 D: 10 F: 14
· Each principal and subsidiary level fills up before the next one.
· When the 3P energy level is full, the 4S fills before the 3D.
· When an atom or an ion has 3D electrons the 4S is written after the 3D, despite it being
filled first.
· Atoms that have 3D electrons always lose 4S electrons first when forming ions.
As well as the order listed above, electron configuration can also be represented with diagrams

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