* Electron Configuration: Sodium has an electron configuration of 2, 8, 1. This means it has two electrons in the first shell, eight in the second shell, and one in the third shell.
* Periodic Trends: Elements in the same group (vertical column) of the periodic table have the same number of valence electrons (electrons in the outermost shell). This means they will also have the same number of electron shells.
Therefore, other elements with three atomic shells are in the same group as sodium (Group 1, also known as the Alkali Metals):
* Lithium (Li)
* Potassium (K)
* Rubidium (Rb)
* Cesium (Cs)
* Francium (Fr)
Important Note: While these elements all have three shells, their atomic sizes increase as you move down the group due to the addition of more electron shells and increasing nuclear charge.
