Periodic Trends: Graphing Melting & Boiling Point
Getting Started
Chemistry teachers use the study of periodic trends to help students recognize the repeating occurrence of
chemical and physical properties of the elements when they are organized in family groups on the periodic
table. This "periodicity" allows a chemist to predict properties of elements and make informed choices in
designing chemical reactions for specific purposes. While chemistry textbooks frequently include discussions
of periodicity for atomic radius, electronegativity and ionization energies, trends also exist for other chemical
and physical properties such as melting and boiling points.
Based on your knowledge of the physical and chemical properties of the elements, how would you expect
melting point and boiling point to vary with increasing atomic number?
To find out, you will graph the melting and boiling points of the elements using a spreadsheet. To begin;
1. Create a folder in your laptop Chemistry folder, entitled: your last name – mp bp graphing task
2. Open the Excel ChemData file (from the wiki) and select Save As from the File menu to save the file
your last name – mp bp graphing task, save it into the desktop folder you created. * Be sure to
continually save it as you update it with the graphs you will create.
3. Save this Word file as your last name – mp bp graphing task
4. Be sure to continuously save this document as you type in your answers to the questions as you go
along.
Graphing Your Data
First, convert melting and boiling point values to the Kelvin temperature scale, in order to eliminate negative
temperatures that may be confusing. Copying the element symbol, atomic number, melting point and boiling
point data from Sheet 1 on the spreadsheet to columns in Sheet 2 will simplify the table.
* Explanation of Degrees Kelvin:
“Temperature is a measure of the average kinetic energy of the particles in an object. Adding energy, eg, heat,
to an object increases the kinetic energy of the particles which is observed as an increase in temperature. When
an object loses energy, kinetic energy of the particles decreases and is observed as a decrease in temperature.
The Kelvin Scale is based on the Kelvin unit (K), the SI unit of temperature. The zero point is absolute zero, the
lowest temperature theoretically obtainable.” (http://www.ausetute.com.au/tempconv.html)
That is, 0K is the temperature at which particles have no kinetic energy. That theoretical temperature is -273K.
Therefore, 0C is 273K. To convert degrees Celsius to degrees Kelvin, add 273 to the number.
Eg, Room temperature, 25C, is: 25 + 273 = 298K.
Insert a new column between the Celsius melting point and boiling point data columns for calculating the
melting point values in Kelvin. Label this new column "Melting Point, K," and label a last column "Boiling
Point, K." Then use the formula bar to convert Celsius melting and boiling point data to Kelvin by adding 273
to each value in these columns (see a screenshot of Sheet 2 below).
Now that you have created Sheet 2 with the appropriate melting point and boiling point data, you are ready to
create a graph of your data. Select the atomic number, Kelvin melting point, and Kelvin boiling point data from
the chart. Tip: To select the data in all three columns at the same time, first click at the top of the atomic
number column. Then holding down the control button (to select data in nonadjacent columns), click also at the
top of the "Melting Point, K," data and then the "Boiling Point, K," data. Data in all three columns should now
be highlighted.
Select the Chart Wizard (graphing icon button) from the toolbar. Then, select an XY Scatter graph (we chose
"scatter with data point connected by lines without markers").
Follow the additional steps in the Wizard to label the graph, X-axis and Y-axis (see Procedure 3 for an example
of a completed graph). Give your graph a meaningful title.
Analyze Your Graph by typing your answers to the following questions:
1. How would you describe the trend in melting point as the atomic number increases within a period?
2. How would you describe the trend in boiling point as the atomic number increases within a period?
3. What do the low points on the graph represent?
Compare these trends to the properties of the elements in the third period (sodium, atomic number 11 to argon,
atomic number 18).
4. What are the similarities and differences?
To make your graph even more informative, you can label the regions where different phases exist. Type the
label, "Solid," in the equation bar at the top of the screen and click on the green check mark just to the left. The
text will appear on the chart and can be moved to an appropriate location. Repeat these steps for the other phase
labels (liquid and gas).
5. Which elements are liquids at room temperature?
Now create a new XY scatterplot graph with the Chart Wizard including the "Room Temperature" column. It
should now look like this:
Try to identify the physical state at room temperature for each element in the periodic table. Locate the two
elements that exist as liquids at room temperature from your graph. (Check the atomic numbers of the elements
you judge to be liquid at room temperature with a periodic table to see if your deductions are accurate).
6. Which elements enjoy the largest liquid ranges?
7. Which have very small liquid ranges?
Now try to graph the melting and boiling point trend for elements only in Group 1, the alkali metals: (Note that
by selecting the "Symbol" column instead of the "Atomic #" column, the symbols will appear on the X-axis.
For chart type, select "line with markers displayed at each value.")
Compare it to a graph of the melting and boiling point trends for elements in Group 17, the halogens.
8. What differences or similarities do you observe?
Extension Exercise 1
Imagine living on Venus with an ambient temperature of 740 K.
1.1 Determine which elements would have different physical states in this new environment from their
physical states on Earth?
1.2 How many liquid, solid, and gas phase elements would exist on the surface of Venus?
1.3 Imagine how life might be different under these circumstances.
1.4 How successful would you be using a lead tool on Venus?
1.5 The temperature on Uranus is –355 degrees Fahrenheit. Which elements would exist in the gas or liquid
phases on Uranus?
Extension Exercise 2
Create two more graphs, showing the melting point and boiling point data for;
1. the first two groups of elements
2. the first two periods of elements
2.1 Summarise the trends you observe for these elements.
Activity adapted from: http://www.teacherlink.org/content/science/instructional/activities/melting/procedure.html