The periodic table is known to every student. The colored rectangles represent successive elements and their properties. But what determines the place in the layout? Enter the classroom for a chemistry lesson and find out what the Mendeleev table is.
Few can imagine a chemistry or physics lesson without the periodic table. This plaque is a perfect example of the genius of one person that was able to inspire successive generations of scientists who added their own discoveries and built on the resulting foundation. The most important thing is that the project is not finished – new elements are still being added and there is room for more.
What are chemical tables?
Chemical tables are graphical teaching aids showing chemical reactions or models of chemical compounds. This most popular of the chemical tables lists all the elements known today. Most of them are naturally occurring. Some of them were discovered in animate and inanimate matter on Earth. Some are known to science only thanks to the fragments of celestial bodies that fell to the surface of the planet. In addition, the list also includes elements obtained artificially in laboratories.
Both in the past and today, you can sometimes find boards in the form of loops, spirals, pyramids or irregularly shaped. At present, however, the most popular way to represent all elements is through horizontal tables divided into groups and periods. In order to make it easier to find the next elements, they are additionally marked with different colors.
Each item in chemical tables always consists of at least two pieces of information. They are a chemical symbol of the element (e.g. H – hydrogen) and its atomic number. More complex versions of tables may also contain other information. It can be the full name element (in Latin and local language, e.g. hydrogenium, i.e. hydrogen), electronegativity, ionization energy and others.
How was Mendeleev’s chemical table created?
Several other researchers attempted to classify elements before Mendeleev. One of them was Alexandre de Chancourtois. He created the so-called telluric propeller. The name comes from the spiral graphic system he proposed, the central point of which was the tellurium element. The basis for placing an element in a given place was its atomic mass.
A German scientist, also worked on the method of the organization of elements Julius Lothar Meyer. Its composition was created at the same time as Mendeleev’s list. Unlike the Russian scientist, he did not envisage the discovery of new elements. So he did not leave any empty, “spare” places in his chemical table.
Mendeleev’s work was also influenced by the discovery of the law of the octaves by John Newlands. This rule says that after arranging elements according to their atomic mass, every eighth of them shows similar features.
Newlands’ law of octaves had a great influence on Mendeleev’s discovery of the periodic rule. He noticed that the properties of elements repeat cyclically (but not always every 8) depending on their atomic masses.
The discovery of the law of periodicity and the knowledge of the achievements of other researchers allowed Mendeleev to create and publish his chemical table on March 6th, 1869. It contained 90 elements known at the time. He realized that the large differences in atomic masses between elements probably indicate that not all of them have been discovered yet. So he left empty spaces in the system for the next elements. During his lifetime, it turned out that he was right, because gallium, germanium and scandium were discovered.
The pioneering approach to chemistry, which was the expectation of potential discoveries of new elements, the formulation of the law of periodicity and the arrangement of the table made the Mendeleev table the most popular of this type today. This is not the only way to honor an outstanding chemist, one of the elements has been named in his honor – mendelev.
Dmitry Mendeleev – a dreaming genius
Mendeleev’s life work, which is chemical tables, was created over the years. Mentally exhausting scientific work was all the more difficult as it also tormented Mendeleev physically. The researcher allegedly neglected sleep.
Allegedly, it was the dream that turned out to have a salutary effect on the intellectual work of the Russian. Mendeleev was about to dream of the plaque. How was it really? He himself said they were inventions. It cannot be ruled out, however, that the proper rest in some way helped the chemist to develop the appropriate element system.
Why the chemical table looks like this – Niels Bohr
Mendeleev’s table was without a doubt a giant leap forward in the field of chemistry. However, this scientist lived in times when the internal structure of the atom was not yet known. Another eminent scientist studied it – the Danish physicist Niels Bohr.
Even before the First World War , he conducted research which resulted in the description of the atomic nucleus. Thus, he proved the circulation of electrons along the orbit path around the nucleus, the possibility of passing from one orbit to another, and the processes of emission and energy absorption during this process.
Thanks to the works over the structure of an atom, Niels Bohr corrected the Mendeleev table. Due to his discoveries, today it is assumed that the characteristics of elements do not depend on mass but on atomic number.
Moreover, it was Niels Bohr who arranged the chemical elements into groups and periods. The model he proposed was widely accepted, becoming the basis for the construction of chemical tables. For this reason, their other name is the periodic table. Currently, the International Union of Pure and Applied Chemistry (IUPAC) is responsible for the publication of the current version of the periodic table.
Principles of the organization of the periodic table
The modern chemical table classifies chemical elements on the basis of their atomic numbers. This is decisive for the position of the atom on the table number of protons in the nucleus of the atom. This is why the first element is hydrogen. There is only one proton in its nucleus.
Why are protons so important? This is due to the fact that it is precisely these subatomic particles that are an essential component of atomic nuclei. In other words, without protons, both elements and all matter as they are, could not exist.
They make up the further division groups and periods. Groups include elements with similar chemical properties. The periods in turn order them in terms of features that change gradually depending on where they are in the system.
Chemical properties of elements depending on the place in the periodic table
Vertical columns are called groups. This organization of elements is related to the number of electrons in the valence shell, that is, on the outermost part of the atom. The number of electrons largely determines the tendency of a given element to form chemical compounds. The more electrons, the more reactive the element is.
At the top of the group is always an element with the smallest atomic mass at the bottom. The elements placed at the top of the column lend their name to the group below them. For this reason, for example, group 2 is Beryllium. Beryllium has the lowest atomic mass in this group.
The groups are divided into major (1, 2 and 13 to 18), minor (3-12), and lanthanides and actinides. It is related to the type of electrons (which are divided into types: a, d, f, s, p) circulating around the nucleus of a given element. Hence also their name – orbitals.
The periods are in turn horizontal rows of chemical tables. The presence of an element in a given period depends on the number of electrons revolving around the atomic nucleus. This time, however, they are not valence electrons, but those orbiting in orbits closer to him. They affect the repeating properties of elements found in one period.
In order to additionally make it easier to find out about the properties of the elements, individual sets are sometimes marked with colors. Thanks to this, metals, semimetals, non-metals etc. can be found in chemical tables faster.
In the above description of the rules governing the table, there appear some inaccuracies. For example, in group 1 there is a non-metal hydrogen at the top. Nevertheless, the group is named lithium derived from the second element – lithium. Moreover, the last, 18th group, are low-reactive noble gasses. Why are these elements in these very places? Due to the basic method of classification, which is the assignment depending on the atomic number.
Mendeleev’s periodic table is an example of people’s constant striving to classify and organize all elements of nature. Moreover, this procedure was successful. A clear and logical periodic table of elements has been the basis of chemistry for decades. Despite the development of science, it has not lost its relevance, being to this day proof of the genius of Mendeleev, Bohr and other outstanding minds of the nineteenth and twentieth centuries.
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