Investigating Orbitals
Target Audience
AS Chemistry students who are interested in physical chemistry.
Key Concepts
Atomic orbitals, bonding, electronic structure of atoms.
The Activity
As chemists we are all familiar with electronic configurations such as 1s2 2s2 2p6 for neon. The
question is, what exactly is the difference between the 2s sub-shell and the 2p sub-shells, or between
any other shells for that matter?
Atomic orbitals are mathematical functions that describe the properties of electrons in atoms. The x,
y and z axes define a position at which the function has a value that can be positive, zero or negative.
Joining positions with a certain value gives you an isosurface. Zero values of the function are called
nodes. Nodes can be either spherical (so-called radial nodes), or cones or planes (so-called angular
nodes).
Squaring the function gives a measure of electron density. Isosurfaces with a large value can
therefore give you an idea of the space in an atom where the electron density is high, while a node
indicates a region of space where the electron density falls to zero.
In this activity you will investigate atomic orbitals. These are hard to visualize so you are going to use
a modelling program. Once you have an appreciation of the different shapes, try to work out a general
rule to help you predict the number of nodes in the functions.
Background Knowledge
You should be familiar with the notation used in electronic configurations, e.g. 1s2 2s2 2p6 for neon.
Resources
Use this web page http://www-keeler.ch.cam.ac.uk/orc/chapter02/hydrogen/weblink2_2.htm for viewing
atomic orbitals in 3-D, with the ability to rotate the orbital, and to pick the value of the function displayed.
What you see is an isosurface, a surface in 3-D space which shares the same (positive or negative) value
of the function. By altering the particular value displayed, you should gain an understanding of the overall
shape of the orbital.
Outcomes
There are many different possible outcomes to this activity. For example, you could make a poster, or
give a presentation to your class on the different shapes of orbitals. You might like to draw up a table for
different orbitals indicating the number of both angular nodes, and radial nodes and the total nodes. Can
you spot a trend?
Helpful hints
• The total number of nodes (angular and radial) that an orbital has depends on its shell number, or
principal quantum number, n. Find an expression for the total number of nodes.
• Every p orbital has the same number of angular nodes – what is it? What is the number for every d
orbital? And every f orbital? What is the trend?
Going further
There are many sites on the web available showing orbitals. You should now be able to understand the
form of any of these.