# Chemistry - Graphing

## Background

An important part of high school chemistry is working with the periodic table of elements. Through the periodic table, students explore the relationship of atomic configuration to properties such as density, boiling point, melting point, and ionic characteristics. Though students will learn to recognize and use the traditional periodic table, other types of visualizations can be just as valuable to exporing atomic characteristics.

The Web contains a number of good examples of interactive periodic tables. Probably the best known is the Web Elements page. Another periodic table of note is one created here in NC. We are going to use data on atomic mass and density to explore some simple visualizations which can be done with the periodic table.

## Graphing

In order to decide how the data can be appropriately visualized, the variables which make up the data need to be evaluated and an appropriate type(s) of visualization chosen. The notes on visualization principles will help you review this method.

The atomic mass and density information was initially worked up in an Excel spreadsheet, periodxl.zip, and then imported into a DeltaGraph file, periodg4.zip. For the purposes of this exercise, we will enter the data from the Excel spreadsheet into DeltaGraph.

For the first graph, we will create a bar chart for the atomic mass for the first 10 elements. The abreviated names of the elements will be charted opposite the atomic mass. The final graph might look something like this:

Notice that there is a positive linear relationship between atomic mass and atomic number.

Next we are going to do a similar graph, except with the first 54 elements. The bar graphic might look like this:

In this case, the horizontal axis is labeled with atomic number rather than abreviation. Because more than five times as many elements are fit into a graph of a similar size, the bars are much more dense. The density does allow us to clearly see the positive trend, but it might be better seen as a line graph. If you took the same data and graphed it as a line, it might look like:

The same trend can be clearly seen in this line graph.

Next, lets create a line graph of the same 54 elements versus density. The graph might look something like this:

Unlike the monotonic trend of atomic mass, density seems to vary in a quasi-periodic trend.

Another way we might want to look at this data was be as a multiple line graph. For this graph, the data will be rearranged to match the original columns and rows of the periodic table. Because of the way DeltaGraph handles the data, the traditional arrangement of rows and columns are transposed in the DeltaGraph spreadsheet. The end result is of the column location being mapped on the X axis, the density on the Y axis, and the rows represented by different lines. The graph might look like:

This graph more clearly shows the relationship that periodic column location has with density.

## Further Work

An alternative to a multiple line graph, a clustered bar graph could be created from the same data page. This would allow an easier comparison of the density at a particular table column.

In addition to density, multiple line graphs can be also be created for other properties such as boiling point, melting point, etc.

Another way that density can be visualized is to superimpose the coding of density on top of the periodic table. Here is an example from the Web Elements page:

Here, color lightness (not hue or saturation) is used to code the density of the elements. It provides a particularly effective method of showing density trends in the table. Similar diagrams can be created for other elemental properties.

4/15/99