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## Periodic Table Trends: Melting Point and Boiling Point

How would you describe the trend in melting point as the atomic number increases within a period?

Melting points increase and then decrease 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?

Boiling points increase and then decrease as the atomic number increases within a period. Boiling temperatures are generally higher than melting temperatures. The greatest differences between melting and boiling temperatures occur for elements in the middle of the period.

What do the low points on the graph represent?

The low points in the graphical representation mark the Noble gases, found at the ends of every period in the periodic table.

Compare these trends to the properties of the elements in the third period (sodium, atomic number 11 to argon, atomic number 18).

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, 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?

Those elements with the greatest difference between their boiling point and melting point values have the largest liquid range. For example, molybdenum, (# 42) and its family member tungsten, atomic number 74, both have large temperature ranges over which they exist as liquids.

Which have very small liquid ranges?

Those elements with the smallest differences between their boiling and melting temperatures have very small liquid ranges.  For example, the noble gases argon (#18) and krypton (#36).

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