Summary: Periodicity
The goals of this experiment are:
You will be assessed on:
First, you are going to travel back to 1869 and marvel at how the first periodic law and table were born when only 63 elements had been discovered at the time. A 35 year old professor of general chemistry, Dmitri Ivanovich Mendeleev, at the University of St. Petersburg (now Lennigrad) in Russia was shuffling his cards with the properties of each element on each card trying to organize his thoughts for his soon-to-be famous textbook on chemistry. When he realized that if the elements were arranged in the order of their atomic weights, there was a trend in properties that repeated itself several times!
In order to see and find order among the elements, we must have some general acquaintance with them. Elements are made of matter, and matter is defined as anything that has mass and occupies space. This includes everything that you can see and a lot that you cannot. It follows that in order to distinguish between different types of matter (in other words different elements) we have to assess their properties.
There are two types of properties: intensive and extensive. In the former case, intensive properties do not depend on the how much of an element is present but do include state (whether a substance is a solid, liquid or gas), color and chemical reactivity. Extensive properties depend on the quantity of matter present - mass and volume are extensive properties.
Properties can be further categorized as either chemical or physical. A chemical change describes how the substance may change composition, such as spontaneously by combustion or in combination with other substances. On the other hand, physical changes are those properties that can be measured without changing the composition of the matter. Condensation of steam to water is a physical change.
What is there to know about the periodic table? Why is it important? Why does it appear in nearly every science lecture room and labs? Is it just a portrait of an aspect of chemistry or does it serve a useful purpose? Why is the name periodic appropriate? Why is the table arranged in such a way? What are the important features of the table? Does it give order to the approximately 120 known elements?
A superficial glance at the Periodic Table will reveal that all known elements are listed by their chemical symbols. An in depth glance at the Periodic Table yields information on the mass of an atom of the element in atomic mass units (amu) for the molar mass of a mole (
Mendeleev arranged the elements in the Periodic Table in order of increasing atomic number in horizontal rows so that elements with similar properties recur periodically (another words they fall directly beneath each other in the Table). The elements in a given vertical column are referred to as a family or group. The physical and chemical properties of the elements in a given family change gradually as one goes from one element in the column to the next. By observing the trends in properties, the elements can be arranged in the order in which they appear in the Periodic Table.
CAUTION! Sodium reacts very rapidly with water to evolve hydrogen and heat. This is potentially dangerous because of the possibility of the violent explosive reaction of
CAUTION! Sodium causes severe chemical burns when it comes into contact with the skin. Note: Metallic sodium must be stored below the surface of an inert liquid such as kerosene to prevent oxidation by air.
| A. | Mg |
| B. | Cu |
| C. | Zn |
| D. | Ca |
Note: Trapped air bubbles on the metal surfaces are not indicative of a reaction.
CAUTION:
CAUTION: Residual calcium should be discarded in a special container designated by your instructor.
Note: Net ionic equations must balance in mass (atoms) and in total charge on each side of the equation.
CAUTION: The reaction of Ca with HCl is not studied. Residual calcium should be discarded in a special container designated by your instructor.
CAUTION: Some of the test tubes may become very hot. Leave them in the rack/holder while you are making observations.
| A. | 0.5 M
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| B. | 0.5 M
|
| C. | 0.5 M
|
| D. | 0.5 M
|
Clean a spatula wire by dipping it into dilute hydrochloric acid (3M) and then holding it in a hot Bunsen flame. Repeat this until the spatula doesn't produce any color in the flame.
When the spatula is clean, moisten it again with some of the acid and then dip it into a small amount of the solid you are testing so that some sticks to the spatula. Place the spatula back in the flame again.
If the flame color is weak, it is often worthwhile to dip the spatula back in the acid again and put it back into the flame as if you were cleaning it. You often get a very short but intense flash of color by doing that.
Chemicals/Materials:
Record your observations on your report form.
It should be noted that sodium is present as an impurity in many if not most metal salts. Because sodium imparts an especially intense color to a flame, flashes of the sodium may be observed in nearly all solutions tested.
3. Based on your experimental results, arrange Ag, Cu, Zn and Pb in order of increasing strength as reducing agents.
4. Arrange
5. Combine the results from Part 2 and Part 3. Arrange Mg, Cu, Zn, Ca, Ag and Pb in order or increasing strength as reducing agents.
6. If it is found that Ni will deposit on Zn foil, but not on Pb foil when a drop of
| Element | Color in flame |
| Li | |
| Na | |
| K | |
| Rb | |
| Cs | |
| Ca | |
| Sr | |
| Ba | |
| Cu | |
| Pb |
What are the limitations of this test?