Analyzing Boiling and Melting Points for the Elements
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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?
Write your conjecture here:
(If you need to explore the significance of atomic number, groups, and periods on the periodic table, check out
this site: http://www.chem4kids.com/files/elem_pertable.html )
To find out, you will graph the melting and boiling points of the elements using a spreadsheet. To begin, open
the Excel ChemData file and select Save As from the File menu to save the file as CHEMDATA in your folder.
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.
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.
Analyze Your Graph
As you analyze your graph, try to answer the following questions:
How would you describe the trend in melting point as the atomic number increases within a period?
How would you describe the trend in boiling point as the atomic number increases within a period?
What do the low points on the graph represent?
What are the similarities and differences?
To make your graph even more informative, you can label the regions where different phases exist. With the
chart selected, 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, so that your graph looks like the one below.
Which elements are liquids at room temperature?
This is easy to illustrate with your spreadsheet. Go back to Sheet 2 of the spreadsheet and create a column for
"Room Temperature, K." Enter "298" in every cell of this column.
Now create a new XY scatterplot graph with the Chart Wizard including the "Room Temperature" column.
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. The two
elements are bromine, 35, and mercury, 80.)
Which elements enjoy the largest liquid ranges?
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:
What differences or similarities do you observe?
Note that hydrogen clearly does not follow the pattern of the other elements. In fact, hydrogen (which is a gas
at room temperature) is not included in the alkali metals, even though it is located in Group 1 on the periodic
table. For the metals in this group, the melting and boiling temperatures decrease with increasing atomic
number. These metals enjoy rather large liquid temperature ranges.
For the halogens, just the opposite trend is observed. These elements show increasing melting and boiling point
temperatures with increasing atomic number. The small differences between the melting and boiling
temperatures for the halogens indicate that these elements have narrow temperature ranges for their liquid
states.
Extension
What other properties of elements have recognizable periodic trends?
Try graphing some of the other data provided in the Chem Data set to see if you can identify other periodic
trends.
Real World Connections:
Mendeleev's Periodic Table, 1869
Check out Mendeleev's original periodic table at this site:
http://chemlab.pc.maricopa.edu/periodic/foldedtable.html
EnvironmentalChemistry.com: Periodic Table of the Elements.
Comprehensive data on elements including scores of properties, element
names in many languages and most known nuclides is provided by this
periodic table. In addition environmental and chemistry articles round out this
site.
http://klbproductions.com/yogi/periodic/
WebElements
Visit WebElements, a site that claims to be the first periodic table on the
WWW. This web site features a printable version of the periodic table.
http://www.webelements.com/webelements/scholar