Exercise 42. Use the shell model to explain why a lithium atom, Li, is larger than a beryllium atom, Be.
Both lithium and beryllium are in the second period of the periodic table, which means that they each contain two shells of electrons. The nuclear charge of the lithium atom, however, is not as strong as that of the beryllium atom. The electrons of the lithium atom, therefore, are not drawn in as close to the nucleus as are the electrons of the beryllium atom.