Experiences

Periodic table II.

Mária Fabianová

Slovakia

Lower Secondary School

Chemistry

Teaching in class

Direct

Mendeleev did not create his system through one night. It is said that he wrote the elements known at that time at pieces of paper so he could move with them. Only one thing was known about elements at that time – its relative mass. Relative because the real mass of each atom is so small that working with them would be very difficult.
Hence, he arranged them according to their increasing relative atomic mass, but he also made some exceptions. Heavier element put in front of lighter one which resulted from his knowledge and intuition. He even left empty places for elements which had not been discovered yet like germanium and gallium. This discovery just proved the correctness of his system.
Then we only analyse the whole table which is divided into 8 columns – groups which are marked by Roman numerals and 7 rows – periods which are marked by Arabic numerals. This division corresponds with situation in electron envelope of individual elements but because anything about it is in curriculum it is difficult to explain it to students.
Some of the groups have historical names – alkali metals, metals, alkaline earth metals, chalcogen, halogen …
The basic characteristics of each element is its proton number, which states order of the element in PT and then all other facts can students find by themselves.
Whether it is metal or non-metal, then electronegativity is stated which plays an important role in creation of chemical bond, oxidation numbers which are important in generation of equations and names of inorganic compounds. Students who come from elementary schools do not even now symbols of elements.
In IV. V., and VI subgroup is true that group begins with non-metal and ends with typical metal.
Except groups and periods there are two rows of elements: lanthanides which follow after lanthanum and have very similar properties and actinides which follow after actinide. In order not to make the table so long, the numbers are placed under it.
There is 92 elements in the nature, including uranium, Everything after uranium are artificially prepared elements which life span is very small. In order to create a new element it is needed to change the nucleus of an atom.
Since 105. element have chemists argued how to name the new element, as a compromise they choose to sign them only by numbers.
The periodic table is the law which is expressed graphically:
Properties of elements and their compounds are periodically dependant on its proton number.
In “translation” it means that for giver chemical element is decisive its position in PT.
At this for of the law cooperated the Czech chemist Bohuslav Brauner which was a close associate of Mendeleev.
Despite many years of practice I still do not know how students perceive this topic, how much they understand it, but I am afraid that not much. But they are interested in fact that when Mendeleev was angry he throw out his shirts from closet.
Despite doubts ratings for this experience are positive.