Mendeleyev's System of the Elements

The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (number of protons). The standard form of the table comprises an 18-column-by-7-row main grid of elements, with a double row of elements below.

The number of known elements kept on increasing during the 19th century. When chemists began to examine the characteristics of particular elements and compare them with each other, they realized that some elements showed considerable similarities in their chemical and physical characteristics. They began to sort similar elements into groups, organizing the elements within the groups according to their relative atomic weights. The various attempts to organize the elements into a system were; crowned with success in 1869, in the then published a paper "A System of the Elements, arranged according to their Atomic Weights and Functions" by the Russian chemist Dmitri Ivanovich Mendeleyev (1834 – 1907). Independent of Mendeleyev's work, the German chemist, Lothar Meyer (1830 – 1895), had arrived at similar conclusions. Whereas Mendeleyev's system first appeared in German chemistry journals in the spring of 1869, Meyer published his system in December of the same year.

The manner in which Mendeleyev presented his system of the elements in 1869 ordered similar elements in horizontal groupings, like the element group fluorine (F), chlorine (Cl), bromine (Br) and iodine (I).

Mendeleyev himself laid special emphasis on the periodicity of the elements, i.e. the recurrence of characteristics at discrete intervals on a scale where the elements were organized according to their increasing atomic weight. The elements were grouped into "periods". In Mendeleyev's System of 1869 these periods are represented by six vertical columns. In 1871, however, Mendeleyev introduced the horizontal representation of the periodic table, the system with the so-called "short periods". At present, the most usual representation of the table of the elements is in the form of long periods; the first period containing two elements, the second and third periods eight elements each, the fourth and fifth periods eighteen elements each, the sixth period contains thirty-two elements. The seventh period is incomplete.

The System of the Elements, presented in 1869 and 1871, showed a number of gaps. Later on, it was improved. Mendeleyev's System of the Elements was recognized all over the world. Thanks to it many new elements have been discovered and are still being discovered by scientists.

Task 6. Translate the following word-combinations from Russian to English

продолжает увеличиваться, в зависимости от атомного номера, относительный атомный вес, показывать значительное сходство, основная сетка элементов, повторение характерных свойств, некоторое количество свободных мест, успешно завершиться, опубликовать исследование (диссертацию)

Task 7. Find more information and make your presentation on the history and development of the periodical system