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?

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??

Revised on: 09/15/2003 at 15:38:31