Knowledge of the Periodic Table
1.1. Presentation of the periodic table
The periodic table is one of the chemist's everyday tools for retrieving the properties of an element based on its position in this table and the various values associated with it. However, before proceeding to use it, knowledge of several simple keys and of their limits should be acquired and their operation should be mastered.
This table should not be perceived as a visionary anticipation or thought of as being received by a scientist through revelation. It is the result of lengthy and patient efforts sustained by Mendeleev and all the chemists in his time, drawing on the empirical knowledge accumulated throughout the 18th and 19th Centuries by several generations of chemists engaged in the pursuit of this classification, which was supposed to name and organize all the elements. Dozens of scientists should be cited, but in order to keep the presentation simple, only three of them will be mentioned here, namely those whose interventions were essential. The first one was Lavoisier, who in 1789 had formalized the notion of elements, then came Mendeleev, who is recognized as the creator of the periodic table according to his work published in 1869, and finally Moseley, who in 1913 offered the key to the complete form of the periodic table.
The use of the table in the absence of several reading keys may prove discouraging, as it requires great memory and leaves the impression of a series of successive specific cases. Moreover, the method used by chemists in order to memorize the periodic table should differ from the one employed for multiplication tables (it is less mechancal), similar to that applied for memorizing the names, location and characteristics of places encountered every day and which are part of real-life experience, therefore involving every day and which are part of real-life experience, therefore involving
Resorting to deductive presentations of the periodic table does not simplify its acquisition, since the table, though following nearly mathematical laws for some characteristics of the elements, represents a synthesis of all the diversity of nature when it comes to other characteristics.1.2. Construction of the periodic table
In order to allow for a better grasp of the subject, a brief history of the periodic table will be presented, covering five periods that are in our opinion decisive for its elaboration, and whose landmarks are given by the following three important names: Lavoisier, Mendeleev and Moseley.
In the period from Antiquity to the Renaissance, seven metals were known: gold, silver, mercury, copper, iron, lead and tin, as well as several other elements such as sulfur, antimony, arsenic, carbon and phosphorus. By the end of the 17th Century, only these 12 simple substances had been discovered.
Figure 1.1. Discovery of elements throughout the centuries
As the techniques used for analysis evolved, Lavoisier had 23 elements at the beginning of his research work, but their number rapidly increased, so that in 1869 Mendeleev gathered 65 elements in an arrangement that he proposed as the first classification, and then in 1913 Moseley gave the final form of the current periodic table, which contained 88 elements (see Figure 1.1).188.8.131.52. The pioneer: Antoine-Laurent de Lavoisier
In 1789 Lavoisier (1743-1794), with his Elements of chemistry, revolutionized (an action fit for those times) chemistry, being the first to propose a distinction between simple and compound substances. He also advanced the idea that certain chemical products, which cannot be decomposed, should be considered elements. It is safe to consider him the founding father of modern chemistry, given his systematic use of weighing i