Propriedade periodicas

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Periodic Properties of the Elements
Note to the Instructor: This laboratory experiment may be split into two laboratory periods, and can be done solo as a DEMONSTRATION.



Purpose: The purpose of this lab is to observe how certain properties of elements tend toward a periodic similarity when the elements are arranged in order of increasing atomic number; to note that elements (and ions ofthose elements) in the same vertical column (family) of the periodic table have similar properties; to note that elements (and ions of those elements) in different families of the periodic table have fewer similarities and greater differences.

Materials: Samples of elements; description of elements; solid samples of Na and K metals for instructor performed demonstrations. Mg, Ca, and Almetals for student experiments; NaCl, KCl, MgCl2, CaCl2, AlCl3 and steel wool. Reagents include 6MHCl, 0.2M NaCl, 0.2M NaBr, 0.2M NaI, 0.2M Na3PO4, 0.2M Na2CO3, 0.1M AgNO3, 6M HN03, 1M NaOH, and 6M NaOH.

Safety: The alkali and alkaline earth metals are highly reactive. Students should take care in handling calcium and magnesium when they react with water. Wear safety glasses.

Hazardous Waste:Silver is a toxic heavy metal. The contents of all test tubes to which AgNO3 has been added should be disposed of in the heavy metal waste container, DO NOT pour it down the sink.

INTRODUCTION

The periodic table is a central tool in helping us to understand regularities in the behavior of elements and compounds.
In the nineteenth century people noted similarities among variouselements and tried to find a pattern of relationship among them. In 1869 Dimitri Mendeleev of Russia and Lothar Meyer of Germany independently arranged the elements in order of increasing atomic weight and noted that similarities appeared at intervals. In 1913 Henry Moseley, and English scientist, determined the nuclear charge (atomic numbers) of the elements and pointed out that the fundamentalorder of arrangement of the elements should be based on increasing atomic numbers. In the years to come, theories of atomic structure founded on the work of Rutherford and Bohr, and other scientists, were able to relate repeated similarities of behavior with structural similarities.
The periodic table is organized in a way to allow us to study and understand the behavior of groups of elementsrather than individual elements. This makes our study more efficient and, at times, helps us to make predictions about the physical properties of elements that are unsafe, unavailable, or too expensive to work with in the laboratory.
Vertical columns in the periodic table are usually labeled with a Roman numberl and a letter. The first column, for instance, is labeled IA, the second IIA, and so on.Sometimes groups are labeled differently, so you must examine the periodic table carefully.
This laboratory activity does not involve numerical data and calculations. It is qualitative in nature and you will be relying on your skills of observation, inference, and written communication.

PROCEDURE

A. Chemical Reactions of Metals


Complete the Physical Properties of SelectedElements table on the report sheet. Record the state of the elements at normal temperature and pressure, metallic characteristics, and their color. This information is available from a variety of sources found in the library or from your instructors. One very important reference is the CRC Handbook of Chemistry and Physics.


B. Chemical Reactions of Metals

1. Group IA (alkalimetals): Na, K demonstration. These elements are very reactive and not found in nature in the free elemental form. The following equation represents the typical violent reaction between an alkali metal and water.


2 Na + 2 H2O ( 2 NaOH + H2
Record your observations on the report sheet. Using your observations, make a conclusion about the trend in the chemical behavior...
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