# Using Physical Properties to Identify Elements

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Using Physical Properties to Identify Unknown Elements

Teacher Notes

Materials Needed:

   Activated charcoal pellets (aquarium supplies)
   Graduated cylinders (plastic, 50 & 100 mL)
   Silicon pieces (chemical supply)
   Tin pieces (chemical supply)
   Balances (good to at least 0.1g)
   Water
   Conductivity meters
   Magnifying glass

Purpose: How can you use physical properties to identify and unknown group of elements?

Your mission: To correctly identify the four unknown elements. Your only clues:
1) the elements are all representative elements,
2) the elements are all found in the same Group,
3) not all the elements from that Group are present in your samples.

Procedure:
1. Observe the physical appearance of each sample. Note things such as luster (how shiny it
is), is it rough or smooth, does it bend easily, its relative hardness. Record this information on
2. Measure the mass of each sample to the nearest 0.1 g. Record the information on the data
table.
3. Using a conductivity meter, test each sample to see if it conducts electricity.
table as Initial Volume.
5. Carefully place your sample in the graduated cylinder which contains water. Record the
new volume as Final Volume on you data table.

Analysis and Conclusion:
1. How does the conductivity vary within this Group of elements?
2. Using the data you collected, calculate the density of each sample.
3. How does density vary within this Group on the periodic table?
4. How does appearance vary within this Group?
5. To what Group do these elements belong? Explain your answer using the data you
collected as evidence for your conclusion.
6. Identify, by name, the four unknown elements.
7. Which element is missing from this Group?
8. Using the data you collected, predict the following for the missing element: Density,
hardness, luster, conductivity
9. What other properties of these elements, which we were not able to test or observe, could

Modified from State Framework “Chemistry of Climate”
Using Physical Properties to Identify Unknown Elements
Discussion By giving the three clues initially, the students should be able to eliminate groups
17 (only 1 solid – Iodine) and 18 (all gases). Upon observation, groups 1 and 2 should be
eliminated (all metals). As properties are investigated it should become apparent that there is
1 non-metal and 2 definite metals. This should remove group 15 and 16 as they do not have
enough metallic elements in them. One of the elements has a metallic luster, but does not
conduct electricity – making it most likely a metalloid. Only group 14 has 1 non-metal, at least
1 metalloid, and 2 metals. The students should easily be able to place carbon. The density of
the metalloid is very close to carbon, indicating it is the one closer to carbon – silicon. Tin and
lead should be able to be correctly identified by order of density, with the more dense at the
bottom of the group. Germanium is the missing element. The students should be able to
estimate that it would be a metalloid with a density near 5 g/mL.

Modified from State Framework “Chemistry of Climate”

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