Final answer:
Elements in the second row of the periodic table, such as lithium, beryllium, and others up to neon, have two electron shells. Group 2 elements like beryllium have two electrons in their 2s subshell. All elements in Group 2 share this valence shell electron configuration.
Step-by-step explanation:
Elements that have two electron shells can be found in the second row of the periodic table. These include lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne). The atoms of these elements have electrons that occupy only the first and second shells. For example, beryllium (Be), which is part of Group 2 elements, has an electron configuration of 1s²2s², indicating that it has filled both its first shell and its 2s subshell with two electrons each.
The valence shell electron configurations for the elements in the second column of the periodic table, which includes Group 2 elements, typically have two electrons in the 2s subshell. This is characterized by the electron dot diagram of beryllium which resembles that of helium, showing two valence electrons.
The same outer shell structure—two electrons in the s orbital—is shared by all Group 2 elements, regardless of the complexity of their internal electron structure.