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The electron configuration for an element is the arrangement of electrons in the orbits (or shells) of a neutral atom. Shells closer to the nucleus have higher binding energy. For example, there are eleven electrons in a sodium atom (atomic number 11). Scientists have measured the quantities of energy needed to remove these electrons one by one from a sodium atom. It is quite easy to remove the the first electron. The next 8 are difficult to remove. Finally, it becomes really hard to remove the last two electrons, which are held very powerfully because they are the closest to the nucleus. This is just a common representation of electron configuration.
Do you have a periodic table? If so then... Simply look at Group One (the first column) which are the alkali metals. As they are in the same group you know they all have the same number of electrons in the outer shell. Group one elements have one electron in the outer shell. Next look at the periods (rows) this tells you how many shells an atom has. Period 3 elements all have 3 shells. So if you take sodium, it is in period 3 so has 3 shells. Remember the 1st shell has a capacity of 2 electrons, and each after has 8. EAch shell must be full before the next shell can contain electrons. So the electron configuration of sodium is 2:8:1