An as orbital has a spherical shape, though specific details of the probability distribution depend on the value of n. Figure shows cross sectional representation of the probability distribtions of a 1s and 2s orbital. The color shading is darker where the electron is more likely to be found. In the case of a 1s orbital (figure left), the electron is most likely to be found near the nucleus. The shading becomes lighter as the distance from the nucleus increases, indicating that the electron is less likely to be found far from the nucleus.
The orbital does not abruptly end at some particular distance from the nucleus. An atom, therefore, has an indefinite extension or ‘’ size.‘’ We can gauge the ‘’ size‘’ of the orbital by means of the 99% contour. The electron has a 99% probability of being found within the space of the 99% contour (the dashed line in the diagram).
A 2s orbital differs in detail from a 1s orbital. As shown in figure right, the electron in a 2s orbital is likely to be found in two regions, one near the nucleus and the other in a spherical shell about the nucleus. The 99% contour show that the 2s orbital is larger than the 1s orbital.
A cross-sectional diagram cannot portray the three-dimensional aspect of the 1s and 2s atomic orbital.
There are three p orbitals in each subshell, starting with the 2p subshell. All p orbitals have the same basic shape (two lobes arranged along a straight line with the nucleus between the lobes) but differ in their orientations in space. Since the three orbitals are set at right angles to each other, we can show each one as oriented along a different coordinate axis . We denote these orbitals as 2px, 2py, and 2pz. A 2px orbital has its greatest electron probability along the x-axis, a 2py orbital along the y-axis, and a 2pz orbital along the z-axis. Other p orbitals, such as 3p, have this same general shape, with differences in detail depending on n. We will discuss s and p orbital shapes again on chemical bonding.
There are five d orbitals, which have more complicated shapes than s and p orbitals. These are represented in figure.
