How many elements does the original Mendeleev periodic table contain?

What is the Mendeleyev periodic table of elements?
The original Mendeleyev periodic table is a classification of chemical elements developed in 1869 by the Russian chemist Dmitri Mendeleyev. This table is based on the chemical properties of the elements and their increasing order of atomic number. Each chemical element is represented by a cell in the periodic table, which contains information about its atomic mass, atomic number, electronic configuration, number of protons, neutrons and electrons, and chemical properties. From this information, chemists can deduce the properties of the elements and predict them, which has led to important advances in the field of pure and applied chemistry.

The periodic table is an essential tool for chemists, physicists, and other scientists because it provides a universal method of classifying all known elements, whether natural or artificial, stable or radioactive, metallic or nonmetallic. It is even used to find new elements by predicting their electronic structure and properties.

The Mendeleev periodic table is now composed of 118 elements classified by period and group. The periods are the horizontal lines of the table and the groups are the vertical columns. Elements of the same period have the same number of electron layers, while elements of the same group have the same number of electrons on their outer layer.

The groups are also called families of elements and have their own names: alkali, alkaline earth, transition metals, lanthanides, actinides, chalcogen, halogens, nobles, etc. Each family has similar chemical and physical properties because the elements have the same electronic configuration or number of electrons on their outer layer. For example, alkali metals have one electron on their outer layer, while halogens have seven.

Mendeleyev’s original periodic table of the elements was a major advance in chemistry, as it allowed elements to be classified according to their periodicity, that is, their tendency to react in the same way under similar conditions. This periodicity is based on the electronic structure of atoms, which determines their electrical charge and their ability to form bonds. Elements that have the same electronic structure have similar chemical and physical properties.

Some elements were known before the periodic table was developed, such as carbon, hydrogen, helium, oxygen, sodium and calcium. Other elements were discovered later, such as scandium, gallium, strontium, rhenium, indium, barium, selenium, tellurium, polonium and beryllium. Over the years, new elements have been discovered and added to the periodic table, such as nobelium, americium and xenon.

Mendeleev’s original periodic table is a fundamental tool for understanding the atomic structure of matter, the electronic configuration of the elements and their chemical and physical properties. It is used by chemists, physicists and other scientists to classify elements, predict their properties and discover new elements. Today, it remains an essential element of chemistry and is the subject of annual celebrations, such as the International Year of the Periodic Table of Elements in 2019, promoted by the International Union of Pure and Applied Chemistry.