It’s elementary, dear chemist!
Yasmin Jayathirtha
Last time, I had mentioned about using the periodic table as a link between the world of atoms and the world of reactions. This can be done through a study of the development of the periodic table, lab activities and classroom activities.
History of the development of the periodic table:
The hardest thing in chemistry is to be able to visualize what is happening at the molecular level from the observations made in the test tube, beaker or flask. In telling the story of the periodic table, the students see that the scientists have recognized trends in properties and have made the attempt to group elements according to the properties. It would be helpful to tell this as a story and highlight Mendeleev’s achievement as following from others’ attempts and stress the improvements he made. All attempts listed the elements in order of their atomic mass and this showed up the periodic (the repetitive) nature of the properties. Most of these were content to group together elements with similar properties, but Mendeleev highlighted the gradual change across the period too. He also took the properties as fundamental and inverted the mass order when needed (Te & I). He also left gaps when he felt the element had not yet been discovered. He considered the properties of any element to be related to all its neighbours and predicted the properties of the elements that would fill the gaps. The Internet is a very good source for all these details and it is worthwhile, say, to compare the properties of eka – aluminum as proposed by Mendeleev and the actual properties of Gallium. Having made the students familiar with the development of the table, we can use activities to familiarize them with its structure.
- On a blank outline of the periodic table, put in the symbols, names and dates of discovery of the elements.
Have the students use the table to answer questions like these:
When Mendeleev came up with his version of the table in 1869, how many elements were known?
Which elements would the people of the Indus Valley civilization have known?
What about the Moghuls?
Which of the elements are used in their elemental form? How many do you recognize?
Which are the gases at room temperature? Where are they on the table? - Periodic trivia:
List all elements starting with the letter C. Can you figure out how their symbols were got?
If there was an element named after you, what would its symbol be?
Can you spell your name with the symbols? If you can, what kind of a compound is it? - Collect all the elements that you can find.
Easily available: iron, copper, zinc (AA cell cover), silver, gold, tin (solder), sulfur, carbon, lead (from battery).
Available in school labs: sodium, magnesium, phosphorous, iodine, bromine.
Easily synthesized: oxygen, chlorine. Nitrogen and oxygen can be used from air.
These elements will allow us to classify the elements into metals and non- metals based on their properties.
With the solid elements, use malleability or brittleness to classify elements into metals or nonmetals.
Take a small sample of the solid, keep between sheets of paper and hammer it. See whether the substance can be beaten thinner.
Make a conductivity meter (Teacher Plus, August 2010) or use a multimeter. Use a small sample of the element and check if it conducts electricity. What is the correlation between conductivity and malleability?
This is interesting because all metals will conduct; carbon as graphite will also conduct but is brittle. Carbon as charcoal, may or may not conduct. The only commonly available elements that form the part of a group are chlorine (synthesised in a test tube, Teacher Plus, September 2010), bromine and iodine. But they are a beautiful group for showing gradation of properties, from gas to liquid to solid, yellow to brown to purple. This can be used to ask what state will astatine be in at room temperature and what is the colour of flourine?
Other resources:
Since the labs have limited resources to offer, we should turn to the Internet for demonstrations.
- The Periodic Table of Videos by the University of Nottingham shows reactions of many elements.
- Elemental Haiku: Mary Song Lee has composed a haiku for each of the 118 known elements and for 119 (not yet synthesized). science.sciencemag.org
- The Elements by Tom Lehrer. This is a song having as lyrics the names of all the elements up to #102. It is truly beautiful.
- Free printable periodic tables (PDF). https://sciencenotes.org/ periodic- table-pdf-2/
- Dates of discovery. https://sciencenotes.org/periodic-tablediscovery- dates/
The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.
