How it all began?
Many famous eminent chemists at the turn of the 19th and 20th centuries have long noticed that the physical and chemical properties of many chemical elements are very similar to each other. For example, Potassium, Lithium and Sodium are all active metals that, when reacting with water, form active hydroxides of these metals; Chlorine, Fluorine, Bromine in their compounds with hydrogen showed the same valency equal to I and all these compounds are strong acids. From this similarity, the conclusion has long been suggested that all known chemical elements can be combined into groups, and so that the elements of each group have a certain set of physical and chemical characteristics. However, often such groups were incorrectly composed of different elements by different scientists and for a long time Many people ignored one of the main characteristics of elements - their atomic mass. It was ignored because there were and are different various elements, which means it could not be used as a parameter for combining into groups. The only exception was the French chemist Alexandre Emile Chancourtois, he tried to arrange all the elements in a three-dimensional model along a helix, but his work was not recognized by the scientific community, and the model turned out to be bulky and inconvenient.
Unlike many scientists, D.I. Mendeleev took atomic mass (in those days still “Atomic weight”) as a key parameter in the classification of elements. In his version, Dmitry Ivanovich arranged the elements in increasing order of their atomic weights, and here a pattern emerged that at certain intervals of elements their properties periodically repeat. True, exceptions had to be made: some elements were swapped and did not correspond to the increase in atomic masses (for example, tellurium and iodine), but they corresponded to the properties of the elements. The further development of atomic-molecular science justified such advances and showed the validity of this arrangement. You can read more about this in the article “What is Mendeleev’s discovery”
As we can see, the arrangement of elements in this version is not at all the same as what we see in its modern form. Firstly, the groups and periods are swapped: groups horizontally, periods vertically, and secondly, there are somehow too many groups in it - nineteen, instead of the accepted eighteen today.
However, just a year later, in 1870, Mendeleev formed new option table, which is already more recognizable to us: similar elements are arranged vertically, forming groups, and 6 periods are located horizontally. What is especially noteworthy is that in both the first and second versions of the table one can see significant achievements that his predecessors did not have: the table carefully left places for elements that, in Mendeleev’s opinion, had yet to be discovered. The corresponding vacant positions are indicated by a question mark and you can see them in the picture above. Subsequently, the corresponding elements were actually discovered: Galium, Germanium, Scandium. Thus, Dmitry Ivanovich not only systematized the elements into groups and periods, but also predicted the discovery of new, not yet known, elements.
Subsequently, after solving many pressing mysteries of chemistry of that time - the discovery of new elements, the isolation of a group of noble gases together with the participation of William Ramsay, the establishment of the fact that Didymium is not at all an independent element, but is a mixture of two others - more and more new and new table options, sometimes even having a non-tabular appearance. But we will not present them all here, but will present only the final version, which was formed during the life of the great scientist.
Transition from atomic weights to nuclear charge.
Unfortunately, Dmitry Ivanovich did not live to see the planetary theory of atomic structure and did not see the triumph of Rutherford’s experiments, although it was with his discoveries that the new era in development periodic law and the entire periodic table. Let me remind you that from the experiments conducted by Ernest Rutherford, it followed that the atoms of elements consist of a positively charged atomic nucleus and negatively charged electrons orbiting around the nucleus. After determining the charges of the atomic nuclei of all elements known at that time, it turned out that in the periodic table they are located in accordance with the charge of the nucleus. And the periodic law acquired a new meaning, now it began to sound like this:
“The properties of chemical elements, as well as the forms and properties of the simple substances and compounds they form, are periodically dependent on the magnitude of the charges of the nuclei of their atoms”
Now it has become clear why some lighter elements were placed by Mendeleev behind their heavier predecessors - the whole point is that they are so ranked in order of the charges of their nuclei. For example, tellurium is heavier than iodine, but is listed earlier in the table, because the charge of the nucleus of its atom and the number of electrons is 52, while that of iodine is 53. You can look at the table and see for yourself.
After the discovery of the structure of the atom and the atomic nucleus, the periodic table underwent several more changes until it finally reached the form already familiar to us from school, the short-period version of the periodic table.
In this table we are already familiar with everything: 7 periods, 10 rows, secondary and main subgroups. Also, with the time of discovering new elements and filling the table with them, it was necessary to place elements like Actinium and Lanthanum in separate rows, all of them were named Actinides and Lanthanides, respectively. This version of the system existed for a very long time - in the world scientific community almost until the late 80s, early 90s, and in our country even longer - until the 10s of this century.
A modern version of the periodic table.
However, the option that many of us went through in school turns out to be quite confusing, and the confusion is expressed in the division of subgroups into main and secondary ones, and remembering the logic for displaying the properties of elements becomes quite difficult. Of course, despite this, many studied using it, becoming doctors of chemical sciences, but in modern times it has been replaced by a new version - the long-period one. I note that this particular option is approved by IUPAC ( international union theoretical and applied chemistry). Let's take a look at it.
Eight groups have been replaced by eighteen, among which there is no longer any division into main and secondary, and all groups are dictated by the location of electrons in the atomic shell. At the same time, we got rid of double-row and single-row periods; now all periods contain only one row. Why is this option convenient? Now the periodicity of the properties of elements is more clearly visible. The group number essentially denotes the number of electrons in external level, in connection with which all the main subgroups of the old version are located in the first, second and thirteenth to eighteenth groups, and all the “former secondary” groups are located in the middle of the table. Thus, it is now clearly visible from the table that if this is the first group, then these are alkali metals and no copper or silver for you, and it is clear that all transit metals clearly demonstrate the similarity of their properties due to the filling of the d-sublevel, which has a lesser effect on external properties, as well as lanthanides and actinides, exhibit similar properties due to only the different f-sublevel. Thus, the entire table is divided into the following blocks: s-block, on which s-electrons are filled, d-block, p-block and f-block, with d, p, and f-electrons filled respectively.
Unfortunately, in our country this option has been included in school textbooks only in the last 2-3 years, and even then not in all of them. And in vain. What is this connected with? Well, firstly, with the stagnant times in the dashing 90s, when there was no development at all in the country, not to mention the education sector, and it was in the 90s that the world chemical community switched to this option. Secondly, with slight inertia and difficulty in perceiving everything new, because our teachers are accustomed to the old, short-period version of the table, despite the fact that when studying chemistry it is much more complex and less convenient.
An extended version of the periodic table.
But time does not stand still, and neither do science and technology. The 118th element of the periodic table has already been discovered, which means that we will soon have to open the next, eighth, period of the table. In addition, a new energy sublevel will appear: the g-sublevel. Its constituent elements will have to be moved down the table, like the lanthanides or actinides, or this table will have to be expanded twice more, so that it will no longer fit on an A4 sheet. Here I will only provide a link to Wikipedia (see Extended Periodic Table) and will not repeat the description of this option once again. Anyone interested can follow the link and get acquainted.
In this version, neither f-elements (lanthanides and actinides) nor g-elements ("elements of the future" from Nos. 121-128) are placed separately, but make the table 32 cells wider. Also, the element Helium is placed in the second group, since it is part of the s-block.
In general, it is unlikely that future chemists will use this option; most likely, the periodic table will be replaced by one of the alternatives that are already being put forward by brave scientists: the Benfey system, Stewart’s “Chemical Galaxy” or another option. But this will only happen after reaching the second island of stability of chemical elements and, most likely, it will be needed more for clarity in nuclear physics than in chemistry, but for now, the good old periodic system of Dmitry Ivanovich will suffice for us.
Periodic table of chemical elements (periodic table)- classification of chemical elements, establishing the dependence of various properties of elements on the charge of the atomic nucleus. The system is a graphic expression of the periodic law established by the Russian chemist D. I. Mendeleev in 1869. Its original version was developed by D.I. Mendeleev in 1869-1871 and established the dependence of the properties of elements on their atomic weight (in modern terms, on atomic mass). In total, several hundred options for depicting the periodic table (analytical curves, tables, geometric shapes and so on.). IN modern version system, it is assumed that elements are brought together into a two-dimensional table, in which each column (group) defines the main physicochemical characteristics, and the lines represent periods that are somewhat similar to each other.
Periodic table of chemical elements by D.I. Mendeleev
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The discovery made by the Russian chemist Mendeleev played (by far) the most important role in the development of science, namely in the development of atomic-molecular science. This discovery made it possible to obtain the most understandable and easy-to-learn ideas about simple and complex chemical compounds. Only thanks to the table do we have the concepts about the elements that we use in modern world. In the twentieth century, the predictive role of the periodic system in assessing chemical properties, transuranium elements, shown by the creator of the table.
Developed in the 19th century, periodic table Mendeleev in the interests of the science of chemistry, gave a ready-made systematization of types of atoms for the development of PHYSICS in the twentieth century (physics of the atom and the nucleus of the atom). At the beginning of the twentieth century, physicists, through research, established that the atomic number (also known as atomic number) is also a measure electric charge atomic nucleus of that element. And the number of the period (i.e., horizontal series) determines the number of electron shells of the atom. It also turned out that the number of the vertical row of the table determines the quantum structure of the outer shell of the element (thus, elements of the same row are obliged to have similar chemical properties).
The discovery of the Russian scientist marked a new era in the history of world science; this discovery allowed not only to make a huge leap in chemistry, but was also invaluable for a number of other areas of science. The periodic table provided a coherent system of information about the elements, based on it, it became possible to draw scientific conclusions, and even anticipate some discoveries.
Periodic Table One of the features of the periodic table is that the group (column in the table) has more significant expressions of the periodic trend than for periods or blocks. Nowadays, the theory of quantum mechanics and atomic structure explains the group nature of elements by the fact that they have the same electronic configurations of valence shells, and as a result, elements that are located within the same column have very similar (identical) features electronic configuration, with similar chemical features. There is also a clear tendency for a stable change in properties as the atomic mass increases. It should be noted that in some areas of the periodic table (for example, in blocks D and F), horizontal similarities are more noticeable than vertical ones.
The periodic table contains groups that are assigned serial numbers from 1 to 18 (from left to right), according to the international group naming system. In the past, Roman numerals were used to identify groups. In America, there was a practice of placing after the Roman numeral, the letter “A” when the group is located in blocks S and P, or the letter “B” for groups located in block D. The identifiers used at that time are the same as the latter the number of modern indexes in our time (for example, the name IVB corresponds to elements of group 4 in our time, and IVA is the 14th group of elements). IN European countries At that time, a similar system was used, but here, the letter “A” referred to groups up to 10, and the letter “B” - after 10 inclusive. But groups 8,9,10 had ID VIII, as one triple group. These group names ceased to exist after the 1988 new system IUPAC notation, which is still used today.
Many groups received unsystematic names of a herbal nature (for example, “alkaline earth metals”, or “halogens”, and other similar names). Groups 3 to 14 did not receive such names, due to the fact that they are less similar to each other and have less compliance with vertical patterns; they are usually called either by number or by the name of the first element of the group (titanium, cobalt, etc.) .
Chemical elements belonging to the same group of the periodic table show certain trends in electronegativity, atomic radius and ionization energy. In one group, from top to bottom, the radius of the atom increases as the energy levels are filled, the valence electrons of the element move away from the nucleus, while the ionization energy decreases and the bonds in the atom weaken, which simplifies the removal of electrons. Electronegativity also decreases, this is a consequence of the fact that the distance between the nucleus and valence electrons increases. But there are also exceptions to these patterns, for example, electronegativity increases, instead of decreasing, in group 11, in the direction from top to bottom. There is a line in the periodic table called “Period”.
Among the groups, there are those in which horizontal directions are more significant (unlike others in which vertical directions are more important), such groups include block F, in which lanthanides and actinides form two important horizontal sequences.
Elements show certain patterns in atomic radius, electronegativity, ionization energy, and electron affinity energy. Due to the fact that for each subsequent element the number of charged particles increases, and electrons are attracted to the nucleus, the atomic radius decreases from left to right, along with this the ionization energy increases, and as the bond in the atom increases, the difficulty of removing an electron increases. Metals located on the left side of the table are characterized by a lower electron affinity energy indicator, and accordingly, on the right side the electron affinity energy indicator is higher for non-metals (not counting the noble gases).
Different regions of the periodic table, depending on which shell of the atom the last electron is located on, and in view of the importance of the electron shell, are usually described as blocks.
The S-block includes the first two groups of elements (alkali and alkaline earth metals, hydrogen and helium).
The P-block includes the last six groups, from 13 to 18 (according to IUPAC, or according to the system adopted in America - from IIIA to VIIIA), this block also includes all metalloids.
Block - D, groups 3 to 12 (IUPAC, or IIIB to IIB in American), this block includes all transition metals.
Block - F, is usually placed outside the periodic table, and includes lanthanides and actinides.
The discovery of the periodic table of chemical elements by Dmitri Mendeleev in March 1869 was a real breakthrough in chemistry. The Russian scientist managed to systematize knowledge about chemical elements and present them in the form of a table, which schoolchildren are still required to study in chemistry lessons. The periodic table became the foundation for the rapid development of this complex and interesting science, and the history of its discovery is shrouded in legends and myths. For all those interested in science, it will be interesting to know the truth about how Mendeleev discovered the table of periodic elements.
History of the periodic table: how it all began
Attempts to classify and systematize known chemical elements were made long before Dmitry Mendeleev. Such famous scientists as Döbereiner, Newlands, Meyer and others proposed their systems of elements. However, due to a lack of data on chemical elements and their correct atomic masses, the proposed systems were not entirely reliable.
The history of the discovery of the periodic table begins in 1869, when a Russian scientist at a meeting of the Russian Chemical Society told his colleagues about his discovery. In the table proposed by the scientist, chemical elements were arranged depending on their properties, ensured by the size of their molecular weight.
An interesting feature of the periodic table was also the presence of empty cells, which in the future were filled with open chemical elements predicted by the scientist (germanium, gallium, scandium). Since the discovery of the periodic table, additions and amendments have been made to it many times. Together with the Scottish chemist William Ramsay, Mendeleev added a group of inert gases (group zero) to the table.
Subsequently, the history of Mendeleev's periodic table was directly related to discoveries in another science - physics. Work on the table of periodic elements continues to this day, and modern scientists add new chemical elements as they are discovered. The importance of Dmitry Mendeleev’s periodic system is difficult to overestimate, since thanks to it:
- Knowledge about the properties of already discovered chemical elements was systematized;
- It became possible to predict the discovery of new chemical elements;
- Such branches of physics as atomic physics and nuclear physics began to develop;
There are many options for depicting chemical elements according to the periodic law, but the most famous and common option is the periodic table familiar to everyone.
Myths and facts about the creation of the periodic table
The most common misconception in the history of the discovery of the periodic table is that the scientist saw it in a dream. In fact, Dmitri Mendeleev himself refuted this myth and stated that he had been pondering the periodic law for many years. To systematize the chemical elements, he wrote out each of them on a separate card and repeatedly combined them with each other, arranging them in rows depending on their similar properties.
The myth about the scientist’s “prophetic” dream can be explained by the fact that Mendeleev worked on the systematization of chemical elements for days on end, interrupted by short sleep. However, only the hard work and natural talent of the scientist gave the long-awaited result and provided Dmitry Mendeleev with worldwide fame.
Many students at school, and sometimes at university, are forced to memorize or at least roughly navigate the periodic table. To do this, a person must not only have good memory, but also to think logically, connecting elements into separate groups and classes. Studying the table is easiest for those people who constantly keep their brain in good shape by undergoing training on BrainApps.
One of the most popular tables in the world is the periodic table. Each cell contains the names of chemical elements. A lot of effort went into its development. After all, this is not just a list of substances. They are ordered according to their properties and features. And now we will find out how many elements are in the periodic table.
History of table creation
Mendeleev was not the first scientist to decide to structure the elements. Many have tried. But no one could compare everything in one coherent table. We can call the date of the discovery of the periodic law February 17, 1869. On this day, Mendeleev showed his creation - a whole system of elements ordered based on atomic weight and chemical characteristics.
It is worth noting that the brilliant idea did not come to the scientist one lucky evening while working. He really worked for about 20 years. Again and again I went through cards with elements, studying their characteristics. Other scientists also worked at the same time.
The chemist Cannizzaro proposed in his own name the theory of atomic weight. He argued that it is these data that can build all substances in in the right order. Further, scientists Chanturquois and Newlands, working in different parts of the world, came to the conclusion that by placing elements by atomic weight, they begin to additionally unite in other properties.
In 1869, other examples of tables were presented along with Mendeleev. But today we don’t even remember the names of their authors. Why is that? It's all about the scientist's superiority over his competitors:
- The table had more open items than the others.
- If an element did not fit the atomic weight, the scientist placed it based on other properties. And it was the right decision.
- There were many empty spaces in the table. Mendeleev deliberately made omissions, thereby taking away a piece of glory from those who would find these elements in the future. He even gave a description of some still unknown substances.
The most important achievement is that this table is indestructible. It was created so brilliantly that any discoveries in the future will only complement it.
How many elements are in the periodic table
Every person has seen this table at least once in their life. But here's what to call exact amount substances are difficult. There can be two correct answers: 118 and 126. Now we will figure out why this is so.
In nature, people have discovered 94 elements. They didn't do anything with them. We just studied their properties and features. Most of them were in the original periodic table.
The other 24 elements were created in laboratories. There are 118 pieces in total. Another 8 elements are only hypothetical options. They are trying to invent or obtain them. So today, both the option with 118 elements and with 126 elements can be safely called.
- The scientist was the seventeenth child in the family. Eight of them died in early age. My father passed away early. But the mother continued to fight for the future of her children, so she was able to place them in good educational institutions.
- He always defended his opinion. He was a respected teacher at the universities of Odessa, Simferopol and St. Petersburg.
- He never invented vodka. Alcoholic drink was created long before the scientist. But his doctorate was devoted to alcohol, and hence the legend developed.
- Mendeleev never dreamed of the periodic table. It was the result of hard work.
- He loved making suitcases. And brought my hobby to high level skill.
- During his entire life, Mendeleev could get 3 times Nobel Prize. But it all ended with just nominations.
- This will surprise many, but work in the field of chemistry takes up only 10% of a scientist’s total activities. He also studied aerostats and shipbuilding.
The periodic table is an amazing system of all the elements that have ever been discovered by people. It is divided into rows and columns to make it easier to learn all the elements.
P.S. The article - How many elements are in the periodic table, published in the section -.
The periodic table is one of greatest discoveries humanity, which made it possible to organize knowledge about the world around us and discover new chemical elements. It is necessary for schoolchildren, as well as for anyone interested in chemistry. Besides, this scheme is indispensable in other areas of science.
This diagram contains everything known to man elements, and they are grouped depending on atomic mass and serial number
. These characteristics affect the properties of the elements. In total, there are 8 groups in the short version of the table; the elements included in one group have very similar properties. The first group contains hydrogen, lithium, potassium, copper, whose Latin pronunciation in Russian is cuprum. And also argentum - silver, cesium, gold - aurum and francium. The second group contains beryllium, magnesium, calcium, zinc, followed by strontium, cadmium, barium, and the group ends with mercury and radium.
The third group includes boron, aluminum, scandium, gallium, followed by yttrium, indium, lanthanum, and the group ends with thallium and actinium. The fourth group begins with carbon, silicon, titanium, continues with germanium, zirconium, tin and ends with hafnium, lead and rutherfordium. The fifth group contains elements such as nitrogen, phosphorus, vanadium, below are arsenic, niobium, antimony, then comes tantalum, bismuth and completes the group with dubnium. The sixth begins with oxygen, followed by sulfur, chromium, selenium, then molybdenum, tellurium, then tungsten, polonium and seaborgium.
In the seventh group, the first element is fluorine, followed by chlorine, manganese, bromine, technetium, followed by iodine, then rhenium, astatine and bohrium. The last group is the most numerous. It includes gases such as helium, neon, argon, krypton, xenon and radon. This group also includes metals iron, cobalt, nickel, rhodium, palladium, ruthenium, osmium, iridium, and platinum. Next come hannium and meitnerium. The elements that form the actinide series and lanthanide series. They have similar properties to lanthanum and actinium.
This scheme includes all types of elements that are divided into 2 large groups – metals and non-metals, having different properties. How to determine whether an element belongs to one group or another will be helped by a conventional line that must be drawn from boron to astatine. It should be remembered that such a line can only be drawn in full version tables. All elements that are above this line and are located in the main subgroups are considered non-metals. And those below, in the main subgroups, are metals. Metals are also substances found in side subgroups. There are special pictures and photos in which you can familiarize yourself in detail with the position of these elements. It is worth noting that those elements that are on this line exhibit the same properties of both metals and non-metals.
A separate list is made up of amphoteric elements, which have dual properties and can form 2 types of compounds as a result of reactions. At the same time, they manifest both basic and acid properties. The predominance of certain properties depends on the reaction conditions and substances with which the amphoteric element reacts.
It is worth noting that this scheme, in its traditional design of good quality, is colored. Wherein different colors for ease of orientation are indicated main and secondary subgroups
. Elements are also grouped depending on the similarity of their properties.
However, nowadays, along with the color scheme, the black and white periodic table of Mendeleev is very common. This type is used for black and white printing. Despite its apparent complexity, working with it is just as convenient if you take into account some of the nuances. So, in this case, you can distinguish the main subgroup from the secondary one by differences in shades that are clearly visible. In addition, in the color version, elements with the presence of electrons on different layers are indicated different colors.
It is worth noting that in a single-color design it is not very difficult to navigate the scheme. For this purpose, the information indicated in each individual cell of the element will be sufficient.
The Unified State Exam today is the main type of test at the end of school, which means that preparation for it must be given Special attention. Therefore, when choosing final exam in chemistry, you need to pay attention to materials that can help you pass it. As a rule, schoolchildren are allowed to use some tables during the exam, in particular, the periodic table in good quality. Therefore, in order for it to bring only benefits during testing, attention should be paid in advance to its structure and the study of the properties of the elements, as well as their sequence. You also need to learn use the black and white version of the table so as not to encounter some difficulties in the exam.
In addition to the main table characterizing the properties of elements and their dependence on atomic mass, there are other diagrams that can help in the study of chemistry. For example, there are tables of solubility and electronegativity of substances. The first can be used to determine how soluble a particular compound is in water at normal temperature. In this case, anions are located horizontally - negatively charged ions, and cations - that is, positively charged ions - are located vertically. To find out degree of solubility of one or another compound, it is necessary to find its components using the table. And at the place of their intersection there will be the necessary designation.
If it is the letter "r", then the substance is completely soluble in water in normal conditions. If the letter “m” is present, the substance is slightly soluble, and if the letter “n” is present, it is almost insoluble. If there is a “+” sign, the compound does not form a precipitate and reacts with the solvent without residue. If a "-" sign is present, it means that such a substance does not exist. Sometimes you can also see the “?” sign in the table, then this means that the degree of solubility of this compound is not known for certain. Electronegativity of elements can vary from 1 to 8; there is also a special table to determine this parameter.
Another useful table is the metal activity series. All metals are located in it according to increasing degrees of electrochemical potential. The series of metal voltages begins with lithium and ends with gold. It is believed that the further to the left a metal occupies a place in a given row, the more active it is in chemical reactions. Thus, the most active metal Lithium is considered an alkaline metal. The list of elements also contains hydrogen towards the end. It is believed that the metals located after it are practically inactive. These include elements such as copper, mercury, silver, platinum and gold.
Periodic table pictures in good quality
This scheme is one of the largest achievements in the field of chemistry. Wherein there are many types of this table– short version, long, as well as extra-long. The most common is the short table, but the long version of the diagram is also common. It is worth noting that the short version of the circuit is not currently recommended for use by IUPAC.
In total there were More than a hundred types of tables have been developed, differing in presentation, form and graphical representation. They are used in different fields of science, or are not used at all. Currently, new circuit configurations continue to be developed by researchers. The main option is either a short or long circuit in excellent quality.