Mendeleev's Periodic Chart

Discussion: Part A
Dimetri Mendeleev arranged the elements by atomic mass and properties in his periodic table. His operating principle was that if the elements are arranged in order of increasing atomic weight the properties would repeat in a regular fashion. (Note he used atomic weight, today we use atomic number which is slightly better.) His work was published in 1871 some 25 years before the discovery of the electron. The families of elements in his chart have similar properties with these properties changing in a systematic way as we proceed from one element to another within each family. One of the things that Mendeleev was successful at doing was to predict the properties of unknown elements. In fact, he even instructed investigators where to look for these undiscovered elements.

In this experiment, you will be presented with the properties of eighteen "known" elements or compounds and ten "unknowns". You are asked to place the "unknowns" in appropriate positions in their respective families by correlating the properties of these elements with the properties of the "knowns" in each family.

Discussion: Part B
When Mendeleev constructed his periodic chart he grouped the elements in families because these elements showed similar chemical and physical properties. There are many other periodic trends that can be studied. We will take a look in this experiment at the acid and basic behavior of the elements. The plan is to mix certain oxides of the elements with water to determine which of these oxides produce an acidic solution and which produce a basic solution. Acid elements are those whose oxides react with water to form acidic solutions; while basic elements are those whose oxides react with water to form basic solutions.

Procedure: Part A
1. Examine the samples of "knowns" on the next page and record properties missing on the worksheet.
2. Examine the samples of "unknowns" and using the worksheet, locate these "unknowns" in their proper positions on the chart.
3. Note that the families of elements included in this experiment are only families IA, IIA, IB, IVA, VIIA, and VIIIA.
4. It is not within the spirit of this experiment to refer to additional sources of information other than a periodic chart.
Knows for Part A
Period Properties I A II A I B IV A VII A VIII A
1 name
physical state
density (G/mL)
hardness
conductivity
melting pt. (C)
solubility (water)
color













N/A







N/A







N/A







N/A


He
gas
0.00018

very poor
-269
none
colorless
2 name
physical state
density (G/mL)
hardness
conductivity
melting pt. (C)
solubility (water)
color
Lithium
solid
0.534
soft
good
180
reacts














N/A


Carbon

2.24
soft-brittle
fair
3237
none









Neon
gas
0.00090

very poor
-248
none
colorless
3 name
physical state
density (G/mL)
hardness
conductivity
melting pt. (C)
solubility (water)
color
Sodium

0.971
soft
good
98
rapid reaction
MgCl2

2.33
brittle
none
708
good






N/A










Chlorine
gas
0.00321

very poor
-101
slight
yel-green
Argon
gas
0.00178

very poor
-189
none
colorless
4 name
physical state
density (G/mL)
hardness
conductivity
melting pt. (C)
solubility (water)
color
Potassium

0.86
soft
good
64
explodes

CaCl2

2.15
brittle
none
772
good

Copper

8.96
soft
excellent
1083
none









Bromine

3.12

very poor
-7.2
negligible









5 name
physical state
density (G/mL)
hardness
conductivity
melting pt. (C)
solubility (water)
color
















Silver

10.49
soft
excellent
961
none

Tin

7.30
soft
good
232
none

Iodine

4.94
soft
very poor
114
negligible

Xenon
gas
0.00585

very poor
-112
none
colorless
6 name
physical state
density (G/mL)
hardness
conductivity
melting pt. (C)
solubility (water)
color








BaCl2

3.85
brittle
none
925
good









Lead

11.4
soft
good
327
none


















Unknown Elements for Part A
Name Physical State Density (G/mL) Hardness Conductivity Melting Point (C) Solubility Color
A solid 19.3 soft excellent 1063 none yellow
B solid 1.90 brittle none 405 good white
C gas 0.00973 poor -71 none colorless
D gas 0.00373 poor -157 none colorless
E solid 3.05 brittle none 873 good white
F solid 2.33 brittle semi-cond. 1410 none steel-gray
G solid 1.53 soft good 39 explodes silver-metallic
H gas 0.00170 none -220 reacts pale-yellow
I solid 5.32 brittle semi-cond. 937 none gray-white
J solid 1.87 soft good 28 explodes silver-metallic


Procedure: Part B
Select an oxide. Take a sample which is the size of a grain of rice. Place it in the center of a watch glass. Drop distilled water from a medicine dropper onto the oxide until you have made a tiny puddle around the sample. Stir the mixture mashing the oxide with a glass stirring rod. Test the liquid around the oxide with about one-third a piece of litmus paper. Clean your glassware well and repeat this test with each of the other oxides. Record your observations.

Obtain a small sample of sulfur, about the size of half of a green pea. Place the element in the bowl of a clean deflagration spoon. Ignite the sulfur by heating the spoon. Hold the burning element in a bottle that contains a one centimeter layer of distilled water until the sample stops burning. The burning should be done in the hood. Partially close the top of the bottle with a rubber stopper while the burning occurs. This will prevent most of the oxide from escaping. Remove the spoon and secure the stopper. Shake well and test the liquid in the bottom of the bottle with a small pieces of each of the litmus papers provided.

Questions: Parts A and B
1. By referring to the periodic table in you text or the one on the wall in the room, identify each of the unknowns in part A by its appropriate symbol or formula.
2. For part B summarize your results in a table in which you classify the oxides you tested as either acid-forming, base-forming, or no reaction.
3. Find the location on the Periodic Table of the elements which oxides formed a base on reacting with water. Do the same for the elements whose oxides reacted to form an acid. What type of elements are acid-forming elements? What type of elements are base-forming elements? What type of elements are neutral elements? Suggest a reason why the latter group of elements do not form either acidic or basic solutions?


Teacher Notes
This page has been enhanced for Netscape 2.0.

This is a nice exercise to do when studying Mendeleev's Periodic Table. It gives students a chance to apply the Periodic Law and enhances their thinking skills.


 
Questions? Comments??