- Lithium (Li), Sodium (Na) and potassium (k) are the three elements that have only one electron in their outermost shells.
- Magnesium (Mg) and Calcium (Ca) are the two elements that contains two electrons in their outermost shells.
- Neon (Ne), Argon (Ar and Xenon (Xe) are the three elements that contains the filled outermost shells.