Electrons are arranged around the nucleus in shells or energy levels.
- The lowest energy level is shown by the shell that is nearest to the nucleus.
- The electrons in an atom occupy the lowest available energy level.
An energy level can only hold a certain number of electrons.
- The shell nearest to the nucleus can only hold two electrons.
- The second energy level can hold up to eight electrons.
- Once there are eight electrons in the third energy level, the fourth begins to fill up.
You can write the number of electrons in each energy level (electronic structure).
- Start at the first shell.
- Record the numbers in each successive shell.
- The number of electrons in each shell are separated from each other by a comma.
Any one of the elements of the main groups of the periodic table have the same number of electrons in their outermost shell. They are called the outer electrons.
The chemical properties of an element depends on how many electrons it has.
An element's reactivity is determined by the number of electrons it has in its outermost shell.
- Because elements in a particular group have the same number of electrons in its outermost shell, they all react similarly.
The elements in Group 0 of the periodic table are called noble gases.
- They are very unreactive because they have a stable arrangement of electrons with eight electrons in their outermost shell
- except for helium which has two electrons in the outer shell.
That is all!