Lesson 1.9 - Electron Structure
Fitting into shells
Electrons will always fill the inner-most shells first.
This means that they will go into the first shell before the second.
In other words, the electrons occupy the lowest available energy levels (innermost available shells).
Electron configuration
We can represent electrons in an atom using a series of numbers.
The electronic configuration of sodium is:
2,8,1
representing 2 electrons in the first shell, 8 in the second shell, and 1 in the third shell.
Electron diagrams
We can represent electrons in an atom using a diagram.
Sodium is represented as follows:
with 2 in the first shell (energy level), 8 in the second, and 1 in the third.
Shell limits
Electron shells have a maximum number of electrons they can hold.
The table below shows the number of electrons each shell holds (counting from the inside).
1
2
2
8
3
8
Note: you mostly only need to know about the first 3 shells. After that, it gets a bit more complicated (so we don't do it at GCSE).
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