On the other hand, electrons that have only one electron in their valence shells (Group 1 elements) or elements that are just one electron short of having a complete shell (Group 17) are the most reactive. For example, atoms with complete valence shells, the noble gases, are the least chemically reactive. In general, the electrons in valence shells determine how the atom behaves in chemical reactions. The valence shell is the outermost electron shell of an atom. In other words, the farther the shell is from the nucleus, the larger it is, and the higher its average energy. 2.21 C).Īs the electron shells go from 1 to 7, they increase in size and average energy. Sodium (Na), with atomic number eleven, has two electrons in shell 1, eight electrons in shell 2, and one electron in shell 3.Oxygen (O), with atomic number eight, has a total of eight electrons, two in shell 1 and six in shell 2 (Fig.
![periodic table with charges of ions periodic table with charges of ions](http://perso.numericable.fr/vincent.hedberg/periodicity/periodicity_Page_03.jpg)
![periodic table with charges of ions periodic table with charges of ions](https://s3-us-west-2.amazonaws.com/courses-images-archive-read-only/wp-content/uploads/sites/887/2015/04/23211102/CNX_Chem_02_06_IonCharges1.jpg)
The electron shell is the region that the electrons travel in (see Fig. Electrons are in constant motion outside of an atom’s nucleus.