Answer to Question #43139 in Inorganic Chemistry for manoj
what are penultimate shells?
The last sell of an atom or the outermost shell is known as the valence shell. The adjacent shell to the valence shell is called the penultimate shell. In simple words, the outer last shell is valence shell, the last but one shell is penultimate shell. For example, sodium (Na) has three shells (1s22s22p63s1), so its second shell (2s22p6) is called the penultimate shell.