The orbitals occupied by electrons in different subshells differ from each other with regard to their size, shape, and orientation in space. The larger the number of the principal shell, the greater the volume of the corresponding orbital.
For example, a 2s electron has an orbital of greater volume than a 1s electron. However, the orbitals of the higher principal shells overlap those of lower shells. This means that the outer electrons penetrate the regions occupied by inner electrons.
The shape of an s electron orbital is spherical while that of a p electron orbital is dumbbell shaped.
The number of possible orientations of atomic orbitals in space depends to an extent on the shape of the orbital. An s orbital still presents the same appearance to an outside observer since its shape is that of a sphere. Therefore an s orbital is said to be spherically symmetrical and without directional characteristics.
